The platform, called the OpenWater Hub, was developed by Hany A. Elesawy, Ahmed I. Ahmed, Yahia A. AboZaid, and colleagues at institutions affiliated with the Academy of Scientific Research and Technology in Egypt, and described in the journal HardwareX. Its central innovation is architectural rather than exotic: instead of relying on one processor to juggle sensor polling and motor control, the board carries two ATmega128A microcontrollers that operate in complete isolation from one another. One chip, designated MCU1, devotes itself entirely to real-time actuation, generating the pulse-width modulation signals that drive motors and actuators. The other, MCU2, runs a non-interruptible bare-metal loop that handles Modbus RTU polling over an RS485 serial bus, parses raw byte streams from industrial probes, and validates every message with local CRC16 checksums. Because no data-carrying copper traces connect the two chips, electrical noise from motor regulators cannot corrupt serial communications.

That separation matters because half-duplex RS485 networks demand strict timing determinism. The master node must toggle transceiver pins with microsecond precision, and on a single-core logger, a Modbus request blocks the processor, disrupting real-time PWM signals and causing robotic control loops to stutter. The authors point out that single-board computers running Linux introduce packet-colliding timing jitter from context switching, while platforms that tunnel RS485 traffic through packetized networks lose the guaranteed silent intervals that legacy sensors require. By giving each task its own dedicated silicon, the OpenWater Hub sidesteps these failure modes entirely, and the team demonstrated that a soft robotic fish could be driven continuously while RS485 telemetry flowed without a single lost frame.

The board is also unusually generous with power for its price. A fuse-protected 24-volt bus supplies up to 24 watts to sensors, enough to handle the high inrush currents drawn by the mechanical wiper motors inside optical sondes. Four independent LM2576 step-down regulators feed the actuation channels, each delivering up to 3 amps of adjustable voltage, defaulting to 8.85 volts but tunable between roughly 5 and 12 volts by swapping a single resistor. Those PWM outputs can drive brushless electronic speed controllers directly or switch external MOSFETs to power heavy DC water pumps and dosing valves. Input protection comes in two stages: a 24-volt transient voltage suppressor clamps surges, while a 20-volt Zener diode acts as an under-voltage lockout that prevents the logic from booting during brownout conditions.

Perhaps the most radical feature is what the design refuses to do: restrict users. Any sensor that speaks RS485 differential signaling, formats its data as Modbus RTU, and accepts 12 to 24 volts can be attached without vendor approval, from high-end fluorometers to budget-tier pH and temperature probes. Wireless telemetry is equally modular, with two UART sockets that accept LoRa, Wi-Fi, Bluetooth, or cellular radio modules, one per microcontroller, allowing sensor data and robot telemetry to travel on separate frequencies. Researchers retain complete, unencrypted ownership of their high-resolution data, a stark contrast to commercial ecosystems in which users must manually export log files in one-hour segments because the closed software will not do otherwise.

From one board, the team derived four deployment configurations. Case Zero is the fully populated PCB on a bench, serving as an open sandbox for sensor calibration and robotic testing. Case C transforms the hardware into a portable Lab-in-a-Box, housed in an aluminum tool case with a seven-inch touch screen, sixteen splashproof aviation connectors wired to the RS485 bus, and a hybrid power system that switches between mains electricity and a solar-charged 12-volt lead-acid battery boosted to 24 volts. Case A mounts a single board inside an IP66 enclosure atop a floating platform built from nine modular HDPE pontoon cubes and an aluminum truss, powered entirely by a 50-watt solar panel and an MPPT charge controller. Case B stacks a second board into the same enclosure, converting the station into a robotic support hub that relays commands down a 50-meter tether and injects power to tethered underwater vehicles.

The validation data are striking for hardware this inexpensive. The fully assembled core PCB costs $45.60, the portable lab $292.60, and the complete floating station $475.60, figures that undercut commercial relay modules alone, which can push a closed system toward $1,600. During a ten-day continuous benchmark, the hub polled its sensors every 34.1 seconds and transmitted 25,314 telemetry packets, of which 25,308 reached the cloud database, a delivery ratio above 99.97 percent with no hardware timeouts. The high-resolution record even captured transient chemical shifts that the commercial reference meter, limited to one-hour logging intervals, completely missed.

The power analysis reveals both the promise and the constraints of the platform. A LoRa configuration with three sensors attached draws enough energy to exhaust a 108-watt-hour battery in roughly four days without intervention, because the probes themselves impose a combined 577.9-milliwatt load even while the system sleeps. The solution is physical rather than software-based: an optional high-side P-channel MOSFET module, triggered by a single microcontroller pin, cuts power to the sensor array entirely during sleep phases, saving about 13.7 watt-hours per day and extending endurance toward the theoretical maximum of nearly nine days. The authors caution that low-side switching would sever the ground reference and route return currents through the RS485 data lines, destroying the transceiver, a warning they emphasize as a strict physical necessity.

The team is candid about the design’s limits. The shared ground plane precludes galvanic isolation, so seawater intrusion through connectors could create ground loops that skew electrochemical measurements. The 8-bit processors lack hardware floating-point units, ruling out onboard wave spectrum calculations, and the 3-amp-per-channel regulator ceiling means heavy winches or sampling pumps would need external converters. The physical separation of the two microcontrollers also forces builders to choose between a wireless LoRa bridge and a jumper wire, demanding some electronics literacy. Future work will move from controlled test tanks to open-sea deployments, where wave impact, salt corrosion, and biofouling will test the platform’s durability over months rather than days.

Even so, the significance of the release is hard to overstate. Coral reefs shelter at least a quarter of all marine species and anchor a substantial share of the ocean’s roughly 2.5 percent contribution to global GDP, yet monitoring them affordably and densely has remained an unsolved engineering problem. By fusing industrial-grade sensing, deterministic robotics control, and open licensing into a single sub-fifty-dollar board, the OpenWater Hub offers research groups, coastal communities, and citizen scientists a way to build monitoring infrastructure that they own outright, modify freely, and scale from a handheld field kit to an autonomous offshore station without ever asking a vendor for permission.

Subject of Research: An open-source hardware platform for marine robotics support and water quality data acquisition

Article Title: OpenWater Hub: An open-source hardware platform for marine robotics support and water quality data acquisition

Article References: Elesawy, H. A., Ahmed, A. I., AboZaid, Y. A., Said, L. A., Samy, I., & Radwan, A. G. (2026). OpenWater Hub: An open-source hardware platform for marine robotics support and water quality data acquisition. HardwareX, 28, Article e00845. https://doi.org/10.1016/j.ohx.2026.e00845

Image Credits: AI Generated

DOI: 10.1016/j.ohx.2026.e00845

Keywords: open-source hardware, marine robotics, water quality monitoring, RS485, Modbus RTU, ocean observation, coral reefs, microcontrollers, LoRa telemetry, environmental sensing, floating sensor station, HardwareX

The technical logic behind Pearce’s objection is straightforward. In experimental science, hardware cost is a quantifiable variable, just like measurement precision, throughput, or error rate. When a paper describes an open-source instrument, the bill of materials is the specification that makes replication possible. Removing it does not merely soften a claim; it breaks the chain of reproducibility that peer review is supposed to guarantee. A peer-reviewed comparison of cost, reproducibility, and performance, Pearce writes, is no more an endorsement of one product than a methods-comparison paper is an endorsement of one technique. It is part of the scientific record needed for replication, evaluation, and efficient public spending. Demanding its removal forces researchers to publish incomplete research, which he characterizes as fundamentally anti-science and inconsistent with the United States government’s own public-access and open-science policies, which now emphasize free, immediate access to federally funded research outputs and the data underlying them.

The economics at stake are substantial. Peer-reviewed research has repeatedly demonstrated that open-source scientific hardware simply costs less than proprietary equivalents. A recent HardwareX review found average savings of 87 percent overall, rising to 92 percent for 3D-printed tools and 94 percent for tools that combine 3D printing with Arduino-class open-source electronics, while earlier case studies often reported savings in the 90 to 99 percent range. The United States currently spends billions of dollars annually on scientific equipment, much of it proprietary and often manufactured internationally. Pearce points to Finland as a cautionary benchmark: an analysis there found that Finnish science funders could save between 2.84 and 27.7 million euros per year simply by shifting to open-source purchasing. Scaled to the American research enterprise, he argues, a conservative estimate suggests federally funded science could run ten times faster, with ten times more equipment at the same cost, if open hardware became the default.

The letter offers a concrete illustration of what such savings look like in practice. An open-source syringe pump library, developed in the United States, documented a device that can be built for roughly 50 dollars in any American laboratory, while internationally manufactured proprietary equivalents cost 1,500 dollars and in some cases up to 2,500 dollars. Stating that price difference, Pearce insists, is not disparagement of the private sector; it is an empirical fact. That design library was downloaded thousands of times within its first months of publication, producing a calculated substitution valuation of between roughly 1 and 12 million dollars in savings to the scientific community in a single year. Since then, the designs have been downloaded tens of thousands of times, conservatively saving scientists tens of millions of dollars. Censoring such data, Pearce argues, prioritizes the commercial comfort of legacy vendors over the efficiency of government researchers and the success of American small businesses.

A central misunderstanding, according to the letter, is the assumption that open hardware is anti-commercial. By definition, open-source hardware licenses permit anyone, including private enterprises, to study, modify, distribute, make, and sell products based on a published design. Far from competing with industry, federal researchers who publish open designs are providing free, rigorously tested research and development to American small and medium-sized enterprises, enabling those firms to commercialize new products without the crippling overhead of initial prototyping and design. The Open Source Hardware Association, a United States-based organization composed primarily of such enterprises, exists precisely because open licensing can be a viable and profitable business model. Some authors in this field have gone so far as to call for all government-funded hardware research to be open source by default, on the grounds that the public has already paid for it.

The commercial track record cited in the letter is extensive. Arduino, whose open-source microcontroller platform has become the de facto standard for embedded prototyping in laboratories worldwide and underpins countless HardwareX publications, is now owned by Qualcomm, a San Diego-based technology firm with roughly 44 billion dollars in annual revenue. SparkFun Electronics of Boulder, Colorado, grew into a 32-million-dollar-a-year business with 146 employees by selling open-source electronic components and educational kits. Adafruit Industries in New York City generates more than 45 million dollars annually selling open-source hardware. Backyard Brains of Ann Arbor, Michigan, commercialized open-source neuroscience tools first described in peer-reviewed open hardware literature, while Opentrons of Long Island City democratized laboratory automation with open liquid-handling robots that displaced proprietary systems costing an order of magnitude more.

The examples extend into heavy manufacturing and even the military. LulzBot, headquartered and manufactured in Fargo, North Dakota, is an entirely open-source 3D printer manufacturer that has competed directly with proprietary incumbents and is used by the United States Marines, whose motto of improvising, adapting, and overcoming is well served by hardware whose designs can be freely modified and repaired. Adjacent firms have flourished on the same ecosystem: re:3D of Austin, Texas, a spinoff founded by NASA engineers, and MatterHackers of Lake Forest, California, both built thriving businesses around the open-source RepRap 3D printing project, the self-replicating rapid prototyper that catalyzed the modern desktop printing movement. Collectively, Pearce writes, these open hardware firms employ thousands of Americans and generate hundreds of millions of dollars in annual revenue, all built on openly licensed designs. When a federal researcher publishes a low-cost environmental sensor or diagnostic tool, he argues, they are planting the seeds of the next generation of American hardware startups.

Open hardware also carries a strategic dimension that goes beyond price. Because designs can be produced with distributed manufacturing technologies such as 3D printing, CNC milling, laser cutters, and open-source microcontrollers, scientific equipment can be fabricated locally and on demand within the United States. This insulates research supply chains from global disruptions, from pandemics to trade conflicts, and repatriates manufacturing capability that has migrated overseas. A federal grant that once could afford only a single proprietary instrument can instead fund an entire laboratory of open-source equivalents, accelerating discovery across any scientific field the equipment touches. Pearce frames these efficiencies as exactly the kind of fiscal discipline that cost-conscious administrations should champion, suggesting that agencies celebrate open hardware breakthroughs with press releases and awards rather than suppress them.

The letter closes with concrete demands directed at the Bureau Approving Officials. Pearce urges them to permit empirically grounded bills of materials and cost comparisons in manuscripts, to issue written guidance distinguishing comparative scientific analysis from endorsement, and to align manuscript review with agency public-access plans and the broader open-science expectations of the Office of Science and Technology Policy. The underlying principle, he argues, is simple: federal researchers should be allowed to report proudly how they are saving taxpayer money and providing open-source research and development to the American public. Whether the agencies respond by revising their review guidance or by continuing to redact economic data will signal how seriously the United States takes both the openness of its science and the competitiveness of the small manufacturers who depend on it.

The dispute is likely to resonate well beyond the federal bureaucracy. As open-source instruments, from syringe pumps to bioprinters, become mainstream tools in laboratories worldwide, the question of who may publish what about them has become a genuine constraint on the scientific record. Pearce’s letter, published as an editorial in HardwareX, places the issue squarely before the officials who control the clearance of government manuscripts, and before a research community that has watched open hardware deliver documented savings measured in the tens of millions of dollars. The stakes, as he frames them, extend to the integrity of peer review itself: a literature stripped of cost data is a literature that can no longer fully support replication, evaluation, or the efficient use of public funds.

Subject of Research: Open-source scientific hardware and federal censorship of cost data in U.S. government research publications

Article Title: An open letter to the Bureau Approving Officials of the United States government

Article References: Pearce, J. M. (2026). An open letter to the Bureau Approving Officials of the United States government. HardwareX, 27, Article e00825. https://doi.org/10.1016/j.ohx.2026.e00825

Image Credits: AI Generated

DOI: 10.1016/j.ohx.2026.e00825

Keywords: open-source hardware, HardwareX, scientific equipment, censorship, bills of materials, 3D printing, federal research policy, open science, cost savings, distributed manufacturing, small business, peer review

The team behind TinZr, led by Ludvik Alkhoury of the New Jersey Institute of Technology together with colleagues from Weill Cornell Medicine and collaborating institutions, set out to solve a persistent problem in wearable sensing research. Commercial microcontroller boards tend to force compromises: the Seeed XIAO ESP32-C3 is tiny and wireless but lacks a microSD card reader and a standardized connector for plug-and-play sensors; the Adafruit GEMMA v2 is featherweight but has no charging circuitry or storage; the popular Teensy 4.1 offers generous processing power and an SD card slot but no Wi-Fi or Bluetooth and a bulkier footprint. TinZr was engineered to combine all of these missing pieces in a single module sized for wearables.

At the heart of the platform sits Espressif’s ESP32-C3 microcontroller, a single-core RISC-V processor clocked at up to 160 MHz with native 2.4 GHz Wi-Fi and Bluetooth Low Energy 5.0 built in. The designers acknowledge that the chip offers fewer general-purpose input-output pins than larger development boards, but they argue the pin allocation was deliberately optimized for the interfaces that matter most in physiological sensing: digital, analog, I2C, SPI, and UART buses. An onboard QWIIC connector exposes the I2C bus along with power and ground, letting researchers snap on compatible sensors — optical, environmental, or electrophysiological — without touching a soldering iron.

Motion sensing is handled by an STMicroelectronics LSM6DS3TR-C inertial measurement unit, which pairs a three-axis accelerometer with a three-axis gyroscope in a single low-power package. The accelerometer can be configured for full-scale ranges up to plus or minus 16 g, while the gyroscope measures angular rates up to 2000 degrees per second, with output data rates reaching several kilohertz. In practice, the team envisions this motion data serving double duty: capturing physical activity directly and supporting artifact detection, so that movement contamination in physiological recordings can be identified and flagged during mobile experiments.

Power management, often the Achilles heel of battery-powered wearables, is entrusted to a Texas Instruments BQ24075RGTR charging chip with power-path management. This means the device can run from USB power while simultaneously charging its 150 mAh lithium-polymer battery, and can switch seamlessly to battery operation when unplugged — without interrupting a recording. The charge current is set to roughly 100 mA via an external resistor, matched to the small battery’s 0.67C charge rate, with safety timeouts and input current limits configured to stay comfortably within USB power budgets. The resistors can be swapped to accommodate larger batteries for longer studies.

Battery life figures vary dramatically by operating mode. In deep sleep with everything disabled, TinZr sips just 0.376 mA, enough for an estimated 16.6 days of standby on the standard battery. Active idle draws 14.8 mA, or about ten hours. Streaming inertial or physiological data over Bluetooth pushes consumption into the 41 to 61 mA range, yielding runtimes between roughly 2.5 and 3.7 hours depending on the sensor load — for example, 3.13 hours while streaming dual-wavelength photoplethysmography at 100 Hz, and 2.46 hours when acquiring ECG and PPG simultaneously at the highest tested rates. Wi-Fi transmission is the most power-hungry mode at 93 mA, draining the battery in under two hours. The platform also monitors its own battery voltage, enabling firmware-level low-battery warnings or automatic recording stops.

The validation experiments demonstrate why the platform matters for real research. In a multi-modal demonstration, TinZr simultaneously acquired a single-lead electrocardiogram from a MAX30001-based front-end and red and infrared photoplethysmographic signals from a MAX30102 optical sensor, streaming both over Bluetooth while packet timestamps and sample counters kept the mismatched sampling rates aligned for later analysis. The resulting ten-second recording showed crisp cardiac cycles with clearly distinguishable QRS complexes alongside pulsatile PPG waveforms. Separately, inertial recordings captured repetitive hand motion at metronome-controlled frequencies of 50 and 100 beats per minute, with the oscillation rate on the accelerometer and gyroscope traces tracking the tempo precisely.

Wireless reliability testing yielded striking results. A single TinZr transmitting inertial-style data at 100 Hz over Bluetooth recorded zero packet loss across 180-second trials at every distance tested, from under one foot up to twenty feet, both under direct line-of-sight and with a wooden door blocking the signal path. Signal strength, measured as RSSI, degraded with distance and obstruction as expected, falling to around -89 dBm at the far end, yet the connection held throughout. In a swarm-style test, five TinZr devices streamed simultaneously to a single laptop at 10 Hz each — again with zero packet loss across all conditions — demonstrating that coordinated multi-node deployments, from distributed body sensor networks to collaborative robotics, are practical with the stock hardware.

Perhaps the most consequential design decision is accessibility. TinZr is programmed through the Arduino ecosystem using an accompanying library called TinZrConnect, which ships with example sketches covering everything from basic button and LED control to a full communication framework in which multiple devices connect to a central PC hub over Wi-Fi for broadcast and individual addressing. Companion Python-based graphical interfaces — available both as source code and as installable executables — let researchers control recording start and stop and visualize data without writing firmware. The designers also provide 3D-printable enclosure files that house the board and battery in a wearable unit measuring just 29.5 by 29 by 20 millimeters, printable on an entry-level hobbyist 3D printer in PLA plastic.

The team is careful to note the platform’s limits: TinZr provides no medical-grade electrical isolation, is not certified for clinical use, and users connecting sensors to human subjects are responsible for ensuring the complete measurement chain meets applicable safety standards. Within research settings, however, the board’s combination of local storage, wireless flexibility, standardized sensor interfacing, and a $65 price point positions it as a serious alternative to commercial controllers for prototyping wearables, field data collection, and multi-device experiments. With hardware licensed under the CERN Open Hardware Licence and software under GPLv3, and all production files published on Zenodo with OSHWA certification, the barrier to building a custom multi-sensor wearable has arguably never been lower.

Subject of Research: An open-source ESP32-C3 microcontroller platform for multi-modal wearable physiological sensing and wireless data acquisition

Article Title: TinZr: A compact wireless ESP32-C3 platform for multi-modal physiological sensor integration and data acquisition

Article References: Alkhoury, L., Moore, T., Swissler, P., Hill, N. J., Shah, S. A., & Kam, M. (2026). TinZr: A compact wireless ESP32-C3 platform for multi-modal physiological sensor integration and data acquisition. HardwareX, 28, Article e00833. https://doi.org/10.1016/j.ohx.2026.e00833

Image Credits: AI Generated

DOI: 10.1016/j.ohx.2026.e00833

Keywords: TinZr, ESP32-C3, open-source hardware, wearable sensors, physiological monitoring, ECG, PPG, inertial measurement unit, Bluetooth Low Energy, data acquisition, HardwareX, battery-powered electronics

The Electrical Testing Board, described in the open-access journal HardwareX by a research team led by Geu M. Puentes-Conde of the Universidad Autónoma de Ciudad Juárez, is a four-layer FR-4 board measuring 187 by 160 millimeters, complete with an integrated carrying handle and an 88-pin gold-finger edge connector designed for backplane integration. Rather than attempting to replace a full-scale industrial test station, the platform is positioned as a compact, reproducible alternative for circuit prototyping, academic instruction and small-scale manufacturing, where the economics of full in-circuit testing infrastructure remain prohibitive. The hardware is released under the CERN Open Hardware License v2.0, its firmware under the GNU General Public License v3.0, and its documentation under Creative Commons Attribution 4.0.

In-circuit testing verifies the values and structural integrity of individual components soldered onto a board, while functional testing validates the overall operational behavior of the finished device. Both methodologies are indispensable in industry because defects can arise from many sources: improper material handling, components that fall outside parametric tolerances, failures in surface-mount assembly equipment, or simple human error. Commercial systems from vendors such as Keysight Technologies, Teradyne and SPEA apply voltage or current stimuli through test nodes, route the resulting signals through multiplexers and conditioning stages involving amplification, filtering and linearization, and finally digitize the analog result to yield electrical parameters such as resistance, capacitance, inductance, voltage, current and short- or open-circuit status. The new board follows this same architectural logic, but in a radically miniaturized and democratized form.

At the heart of the design is a three-board modular stack. A main PCB houses the functional test modules, a relay PCB carries the switching matrices, and a pluggable MCU PCB hosts the primary controller, a Microchip PIC32MX795F512L running at 80 megahertz. Because the core module is a daughterboard, a failed microcontroller can be swapped in seconds without any desoldering. Two slave PIC18F4620 microcontrollers, managed over the I2C bus, drive the relay matrices and handle auxiliary input and output tasks. Sixteen test nodes connect the device under test to four relay-based switching buses, labeled V+, M+, M− and G−, which route signals among the programmable power supplies, the digital multimeter subsystem, comparators, programmable pull-up and pull-down networks, and protection circuitry. The reed relays at the center of these matrices, Coto 9012-12-11 units, actuate in roughly 0.35 milliseconds, allowing a complete in-circuit or functional measurement cycle of 10 to 50 milliseconds per device.

The measurement capabilities are broad. The onboard digital multimeter offers voltmeter ranges of 0 to 10 volts and 0 to 100 volts through a 16-bit successive-approximation ADC paired with a low-drift 10-volt precision reference, ammeter ranges from 1 microampere to 1 milliampere across three calibrated gain stages built around a transimpedance amplifier, resistance measurements from 0.5 ohms to 1 megohm using a ratiometric voltage-divider method, and capacitance measurements from 10 nanofarads to 220 microfarads. Rather than replicating the expensive AC voltammetry and synchronous phase-detection approach used in commercial systems, the designers adopted a direct interface circuit technique: the unknown capacitor is charged and then discharged through a known reference resistor while an embedded timer measures the interval until a comparator threshold is crossed, from which capacitance follows from simple logarithmic relations. The method trades some accuracy at the low end of the range for dramatic reductions in circuit complexity and cost.

Validation against reference instrumentation suggests the trade-offs are manageable for its intended audience. Benchmarked against an HP 34401A six-and-a-half-digit multimeter, the voltmeter stayed within 0.14 percent relative error at low-voltage test points of 1, 3.3 and 5 volts, with error and variance growing at higher voltages, reaching about 0.91 percent at 90 volts, a divergence the authors attribute to attenuation networks and parasitic loading in the high-voltage path. The ammeter achieved sub-percent errors at points such as 5 microamperes and 150 microamperes, though deviations grew near the top of each subrange. Resistance measurements remained below 1 percent relative error across 1 kilohm to 1 megohm, while the lowest point, 0.5 ohms, showed an 11.31 percent error driven by relay contact resistance, a systematic offset the firmware can compensate through tare calibration. Capacitance accuracy was weakest at 10 nanofarads, with errors above 30 percent, but settled to roughly 8 to 10 percent for bulk values of 100 and 220 microfarads.

Beyond raw metrology, the platform is designed for integration into automated test equipment environments. It communicates with a host computer or programmable logic controller over RS-232, opto-isolated UART buses, or Ethernet through a Microchip LAN8720 physical layer transceiver, using a checksum-protected packet protocol in which command bytes select tasks such as automated testing, limit transmission and data retrieval. Up to 12 boards can be daisy-chained under a single host controller, each addressed by a dedicated digital selection line and monitored through a busy-status output. In a demonstration implementation, eight boards ran parallel end-of-line tests across a multi-cavity fixture pallet, performing power-up sequencing, firmware register extraction over UART, harness continuity checks, battery voltage profiling, quiescent current measurement, pneumatic actuation of buttons via high-current relay outputs, busbar presence verification and even acoustic pattern validation through the onboard audio conditioning circuit, a capability absent from the commercial systems the authors compared against.

The team is candid about the limits of the platform. It supports a single device under test per board, offers 16 test nodes compared with up to 2,592 on a two-module Keysight i3070 system, and its practical analog bandwidth is deliberately limited to DC to 10 kilohertz by the relay switching network. It cannot measure inductance, does not support IEEE 1149.1 JTAG boundary-scan testing, and is not certified for industrial deployment, restricting its scope to controlled laboratory, prototyping and small-production settings operated by qualified engineering personnel. Long-term relay endurance, thermal drift, fault injection robustness and full metrological characterization were also left as explicit future work. Power consumption, however, is modest: roughly 2.5 watts at idle and between 3.1 and 6 watts during typical testing routines.

The economic argument is nevertheless compelling. Where a complete commercial system with instrument cards, chassis and enclosure can run into six figures, the proposed assembly costs about $790 to fabricate, or an estimated $3,500 for a full system including host controller, enclosure, cables and test probes, still roughly an order of magnitude below the entry point of industrial hardware, which typically demands $25,000 to $250,000. All design files, schematics, firmware, bill of materials and even a debugging enclosure are openly available through a public repository, enabling any competent electronics laboratory to replicate or adapt the platform.

The implications extend beyond manufacturing quality control. The authors envision materials scientists using the programmable switching matrices and multimeter to map resistance and capacitance across novel conductive polymers or biological tissue samples, applied physics laboratories replacing bulky benchtop instruments in automated experiments, environmental researchers deploying the opto-isolated inputs and Ethernet interface as a ruggedized sensor node layer, and embedded acoustics teams exploiting the audio conditioning chain for voice and frequency pattern work. Future development will focus on integrating machine learning directly into the firmware layer to shorten test cycles and enable predictive fault isolation, along with expanding the physical node architecture to widen signal routing capacity and test coverage. For a field in which the cost of entry has quietly determined who can afford rigorous electrical verification, an open, sub-$1,000 testing platform may prove to be one of the more quietly disruptive hardware releases of the year.

Subject of Research: A low-cost modular open-hardware PCB assembly for in-circuit and functional testing of electronic devices

Article Title: A low-cost modular PCB assembly for functional and in-circuit testing

Article References: Puentes-Conde, G. M., Sifuentes, E., Molina, J., Enríquez-Aguilera, F., Bravo, G., & Ávila, A. H. (2026). A low-cost modular PCB assembly for functional and in-circuit testing. HardwareX, 28, Article e00844. https://doi.org/10.1016/j.ohx.2026.e00844

Image Credits: AI Generated

DOI: 10.1016/j.ohx.2026.e00844

Keywords: in-circuit testing, functional testing, open-source hardware, printed circuit board, automated test equipment, digital multimeter, relay switching matrix, electronics manufacturing, small and medium enterprises, microcontroller, capacitance measurement, HardwareX

The motivation behind the project lies in a quiet revolution sweeping through structural engineering. Fiber-reinforced thermoplastic composites are increasingly favored over traditional thermoset materials in aerospace, automotive and wind energy applications because they offer exceptional specific strength, corrosion resistance, fatigue tolerance and damage resistance. The aerospace sector in particular has embraced these materials, reporting weight savings of 20 to 30 percent alongside an approximate 25 percent reduction in total production costs. Unlike thermosets, which cure irreversibly, thermoplastic matrices can be melted and re-consolidated, which makes them inherently weldable. That weldability allows large structures to be joined without rivets or adhesives, and it has already transformed flagship aircraft components.

Resistance welding is widely regarded as one of the most efficient and promising techniques for joining these materials. The principle is elegantly simple. An electric current is passed through a resistive heating element placed at the joint interface, and Joule heating, governed by the relationship Q = I²Rt, raises the temperature until the thermoplastic matrix melts. Polymer chains then diffuse across the interface, and the joint consolidates under pressure as the assembly cools. Crucially, even though melting temporarily reduces molecular weight, thermoplastics retain their original mechanical properties once cooled, provided the joint achieves low void content and strong interlaminar bonding. The technology has a distinguished industrial pedigree: the Fokker 50’s main landing gear doors were among the earliest aerospace applications, and the J-nose component on the wing leading edges of the Airbus A340-500/600 and A380 was re-engineered from multiple aluminum pieces into a single polyphenylene sulfide composite weldment, eliminating thousands of rivets and shedding nearly 20 percent of the component’s weight.

Yet resistance welding is notoriously difficult to execute well. Current leakage is a serious risk, especially when welding composites reinforced with conductive carbon fibers. Temperature distribution along the joint interface is rarely uniform, and overheating at the edges can thermally degrade the polymer while the center remains insufficiently melted, producing voids and partially fused zones that weaken the bond. Weld quality is acutely sensitive to pressure and timing, and inadequate parameters can cause joint deconsolidation, excessive resin squeeze-out or fiber displacement. The process also demands access to both sides of the workpiece and highly specific tooling for each component geometry. Conventional alternatives fare no better: mechanical fastening introduces stress concentrations, galvanic corrosion, delamination from drilling and weight penalties, while adhesive bonding requires long curing times, extensive surface preparation and joints whose quality degrades under environmental exposure.

The OpenWelT platform tackles each of these challenges through a combination of clever design and low-cost automation. The machine’s main structure is built from modular aluminum V-slot profiles, providing lightness and portability while the welding base itself is made of wood, chosen deliberately because it acts as both a structural support and an electrical insulator, preventing current from escaping through the machine frame. During operation, external ceramic insulator plates, which are not permanent parts of the equipment, are positioned at the joint interface to serve as thermal barriers, concentrating energy within the weld zone and shielding the wooden base from localized heat. This dual insulation strategy directly addresses the leakage and thermal-control problems that plague conventional setups.

Perhaps the most distinctive innovation is the machine’s autonomous pressure management. Instead of relying on manual pneumatic presses or expensive hydraulic systems, OpenWelT employs an electric linear actuator driven by an Arduino Uno microcontroller that processes signals from a 100-kilogram load cell in real time through an HX711 24-bit amplifier. This closed feedback loop applies and maintains the perpendicular consolidation force with precision and repeatability, eliminating dependence on external pressure systems. The power subsystem pairs a Huawei R4850G2 rectifier with a Juntek DPM8624 programmable buck-boost converter, delivering a regulated welding output of up to 60 volts and 24 amps with fine decimal adjustment, which helps prevent both edge overheating and incomplete melting at the weld center. Galvanic separation between the high-power welding circuit and the low-voltage control electronics ensures that back-electromotive forces and ground loops cannot corrupt the sensitive measurement chain.

The entire apparatus is orchestrated by a custom Python-based graphical interface that acquires voltage, current, power, temperature via a Type-K thermocouple and pressure at one hertz, logging every variable with timestamps and exporting standardized PDF reports alongside raw data files. The software automatically validates each incoming data frame, imposes upper safety limits of 24 amps and 1.5 megapascals, and generates voltage-versus-time curves without requiring expensive laboratory data acquisition boards. Because the firmware and interface are fully open, researchers can freely modify the control algorithms, implement alternative feedback loops or adapt the platform for entirely different experimental setups, something impossible with proprietary commercial stations.

To validate the machine, the team welded three replicate lap-joint specimens of glass fiber-reinforced polyetherimide (GF/PEI) thermoplastic composite according to the ASTM D5868 standard, using 10 volts, 14 amps, 1 megapascal of pressure and a 100-second weld time. The heating element was a woven stainless steel mesh with 40-micrometer wires, cleaned ultrasonically before each run to guarantee reproducible contact resistance. The welded joints achieved a mean lap shear strength of 29.83 ± 1.2 megapascals, with an average power of 45.69 ± 1.1 watts, a power density of 0.14 ± 0.03 W/mm², and an average electrical resistivity of 0.23 ± 0.02 ohms. Optical microscopy of the joint cross-sections revealed excellent interfacial consolidation with only minor porosity, attributed to residual solvent in the matrix or slight thermal gradients, while dark-field imaging confirmed that reinforcing fibers were undamaged, well encapsulated by the polymer and free of delamination. The low coefficient of variation across replicates, roughly 4 percent, demonstrated stable and repeatable performance under fixed conditions.

The implications extend well beyond one material system. The authors envision the platform serving as a general-purpose testbed for any process combining controlled force with localized Joule heating, including heat sealing of polymer films, thermal bonding of textiles and membranes, and thermally activated adhesive curing, requiring only adapted sample fixturing. Because the continuously recorded voltage at constant current is a direct signature of the heating element’s resistance, the machine can also characterize the electrothermal behavior of metallic meshes, conductive coatings and nanocomposite heating elements on their own. For teaching laboratories and institutions without access to industrial welding stations, the complete documentation and low cost make it feasible to prepare standard-compliant specimens and expose students to a full sensor-to-actuator control chain, from load-cell acquisition to automated report generation.

The researchers are candid about current limitations. Validation was performed on a single material system and joint geometry at one optimized parameter set, and thermocouple monitoring is restricted to the 50 to 400 °C range. The serial protocol lacks checksum verification and automatic reconnection, and the software does not yet offer closed-loop temperature control or machine-learning integration. Ongoing work aims to map the wider parameter space of voltage, current, pressure and time. Nevertheless, with hardware licensed under CERN-OHL-S v2.0, software under the MIT License, documentation under CC BY 4.0, and all design files hosted on a public repository, OpenWelT represents a significant democratization of advanced composites manufacturing research, proving that a benchtop machine assembled from off-the-shelf components, printed PETG brackets and reclaimed materials can produce joints of genuine structural quality.

Subject of Research: An open-source, low-cost resistance welding machine for joining and studying thermoplastic composite materials.

Article Title: Open-source modular resistance welding equipment for thermoplastic composites

Article References: Reis, J. F., Barbosa Marques, L. F., Lucas Vieira, M. O., Gomes, D. N., Kotz, T. A., & de Oliveira Hein, L. R. (2026). Open-source modular resistance welding equipment for thermoplastic composites. HardwareX, 28, Article e00839. https://doi.org/10.1016/j.ohx.2026.e00839

Image Credits: AI Generated

DOI: 10.1016/j.ohx.2026.e00839

Keywords: resistance welding, thermoplastic composites, open-source hardware, aerospace materials, GF/PEI, Joule heating, Arduino control, lap shear strength, ASTM D5868, composite joining, HardwareX, low-cost laboratory equipment

The motivation behind the project lies in a persistent bottleneck in materials research. Solution-based printing, the family of techniques that includes inkjet, aerosol jet, gravure and screen printing, underpins modern work on flexible electronics, chemical sensors and printed diagnostics, all of which depend on depositing inks and functional fluids in exact locations on diverse substrates. Commercial tools such as the Fujifilm Dimatix Materials Printer DMP-2850 handle this task admirably, but their price places them beyond many academic groups. Meanwhile, the drive toward self-driving laboratories, where robots, liquid handlers and inline instruments work in concert to accelerate discovery, has exposed another cost barrier: automation platforms like the Opentrons OT-2 robot start at more than 15,000 dollars before a single experiment runs. The CRISP team set out to demonstrate that a frugal twin could be assembled from commodity hardware without sacrificing meaningful performance.

The engineering insight at the heart of the project is that a fused deposition modeling printer already contains nearly everything a liquid-dispensing robot needs. The Ender-3 provides robust three-axis motion control, a stepper motor for extrusion, an Arduino-class motherboard running Marlin firmware, and a mature G-code ecosystem. The researchers removed the hot end, heating block and filament spool holder, then mounted a syringe pump assembly on the printer’s upper frame. That pump is deliberately simple: a stainless-steel trapezoidal lead screw driven by the printer’s stock extruder stepper motor, a brass flanged nut riding on a 3D-printed gantry bracket, and two mounts that clamp a standard 20 milliliter Luer-lock syringe in place. When the motor turns, the threaded rod advances and the gantry bracket pushes the syringe plunger with kinematic regularity, converting rotational steps into volumetric dispensing.

Ink reaches the substrate through a length of fluorinated ethylene propylene tubing, roughly 75 centimeters long with a one-sixteenth-inch inner diameter, which press-fits into a nozzle made from a disposable polypropylene pipette tip. The choice of pipette tips as nozzles is a small piece of design genius: at 10 to 20 cents apiece, they are effectively consumables, and a clogged nozzle is solved by pulling the tip off and pressing on a new one rather than performing delicate surgery on an expensive printhead. The tips used in the demonstration have orifice diameters between roughly 0.35 and 0.50 millimeters, but because deposition is volumetric rather than nozzle-limited, the final droplet size on porous paper is governed mainly by the dispensed volume and how the fluid wicks into the fibers.

Because the syringe pump borrows the printer’s native extruder motor, it is programmed with ordinary G-code, the same command language hobbyists use to print plastic. This gives CRISP a surprisingly sophisticated feature set for its price: the number of programmed dispensing steps is limited only by how many G-code commands a user writes, which allows multi-step routines comparable to those of programmable laboratory pumps that cost several thousand dollars. For calibration, the team primed the tubing through the printer’s own interface, loaded a G-code file onto a microSD card, and let the machine execute its run from file. The comparison point is stark: a Chemyx 4000X programmable syringe pump runs about 4,400 dollars, while CRISP’s pumping hardware costs a fraction of that and integrates directly into a motion platform.

Validation began with a deliberately humble test fluid, a blue dye dissolved in water, chosen so that printing parameters could be optimized without the expense and opacity of metal nanoparticle inks. The team printed repeated five-by-five arrays of droplets on cardstock with dots spaced 20 millimeters apart and a programmed volume of 0.026 milliliters per drop. Quantitative image analysis using the open-source computer vision library OpenCV revealed a mean droplet circularity of 0.87 with a standard deviation of only 0.02, a coefficient of variation of 2.30 percent that indicates highly uniform droplet morphology. Positional accuracy proved equally respectable: the mean deviation between programmed and actual droplet centers was 0.65 millimeters, with a worst case of 1.25 millimeters, and the error distribution was random rather than systematic, confirming that the added syringe hardware introduces no mechanical drift into the printer’s kinematics.

Weighing the droplets provided an independent check on volumetric fidelity. Across five trials in which the system dispensed ten droplets into a tared dish, the average total mass was 265.9 milligrams, implying 26.59 microliters per drop against a kinematic prediction of 26.0 microliters, a percent error of just 2.3 with a coefficient of variation of 1.6 percent. Deposited on porous cardstock, the drops spread into hemispheres averaging about 4.6 millimeters in diameter, exactly matching volumetric expectations. The researchers note that the practical minimum droplet volume for this configuration is roughly 3 to 5 microliters, bounded by the stepper motor’s step resolution and fluid surface tension, though switching to a smaller syringe barrel would stretch that limit further by amplifying plunger travel per dispensed volume.

The team is candid about the platform’s boundaries. The nozzle holder as built maintains a physical gap of about 7 millimeters between tip and substrate, which is ideal for falling droplets but prevents the close tip-to-surface contact needed for a stable meniscus during continuous line printing; attempts to write continuous features with aqueous dye produced lines that thinned and broke. Paper remains the sweet spot because its fibrous structure absorbs liquid quickly, pinning particles before uneven drying can occur, whereas non-porous glass slides exhibited anomalous drying behavior related to well-known evaporative defects such as the coffee ring effect. The dead volume of the delivery tubing, roughly 1.5 milliliters, also matters when working with expensive reagents, and the authors recommend shorter, stiffer tubing and a heated print bed to tame environmental drying variability.

What makes CRISP more than a clever hack is its framing within the growing frugal-twin movement in chemistry and materials science, where low-cost replicas of commercial instruments are validated against their expensive counterparts. Structurally, the design resembles prior Ender-3 liquid-handling conversions, but it differs in relying entirely on stock printer hardware and 3D-printed brackets rather than an external syringe pump, keeping the added cost below 200 dollars. With results showing dispensing circularity of 98.2 percent and relative positional accuracy of 96.8 percent, the authors argue that stepper-driven commodity hardware offers sufficient repeatability for routine patterning tasks. Their ultimate goal is the deposition of metal nanoparticle inks for paper-based sensors, and with every CAD file, STL, G-code script and dataset published under open licenses on the Open Science Framework, CRISP invites laboratories worldwide to print droplets, not just plastic, for the price of a good dinner out.

Subject of Research: A low-cost 3D printer-based platform for precision solution printing on paper-based substrates

Article Title: CRISP: A 3D printer-based platform for precision solution printing on paper-based substrates

Article References: Lutfiyev, I., McCoy, S. A., Star, R., Giordano, A. N., Rist, B., Baldwin, L. A., & Rao, R. (2026). CRISP: A 3D printer-based platform for precision solution printing on paper-based substrates. HardwareX, 28, Article e00842. https://doi.org/10.1016/j.ohx.2026.e00842

Image Credits: AI Generated

DOI: 10.1016/j.ohx.2026.e00842

Keywords: CRISP, 3D printing, syringe pump, solution printing, paper-based substrates, Ender-3, open-source hardware, G-code, droplet deposition, frugal science, flexible sensors, HardwareX

The problem the Allstruder addresses is well known to anyone working in bioprinting, food printing, soft robotics, or electronics fabrication. Commercial extrusion systems generally fall into two camps, each with a fundamental compromise. Volumetrically accurate syringe pumps deliver precise doses but respond sluggishly, while pressure-based syringe extruders build pressure quickly but sacrifice precision. Both categories tend to be expensive, difficult to customize, and poorly matched to the open, modular workflows that dominate academic and educational settings. The result, the authors argue, is a technical barrier that drives labs to build in-house hardware for the same unmet need over and over, undermining reproducibility and accessibility across the community. A graduate student, they note, should not have to spend months developing a bespoke extruder simply to print a new bioink.

The do-it-yourself landscape has not solved this fragmentation. The rise of affordable desktop thermoplastic printers has inspired dozens of creative open-source fluid extrusion designs, but nearly all are tailored to specific materials, machines, or niches, and few generalize across use cases, users, and environments. Labs frequently tailor their workflows to the constraints of a particular extruder, locking themselves into siloed methodologies that limit interoperability and shared progress. Several prior designs nonetheless stand out as foundational. The Replistruder series brought affordable, precise, retractable syringe extrusion to embedded FRESH bioprinting and became the most widely cited and remixed open extruder family, with the Replistruder 3 setting benchmarks for accessibility, the Replistruder 4 adding off-the-shelf metal parts for reliability, and the Replistruder 5 pushing toward high-performance, multi-material use. The Large Volume Extruder handled 50 mL syringes for bulkier pastes such as clays, the Enderstruder converted the ubiquitous Creality Ender 3 into a capable fluid printer at minimal cost, and the pioneering Fab@Home platforms introduced early direct ink writing and extruder retraction concepts.

To evaluate these predecessors systematically, the team developed a five-metric framework covering affordability, performance, simplicity, versatility, and design for 3D printing, decomposing each metric into measurable sub-criteria and scoring every device against them. The published rubric reveals a pattern of deliberate trade-offs rather than failures. The Replistruder 3 scored well on affordability and performance but poorly on simplicity because it demanded considerable expertise. The Replistruder 4 traded fully printed construction for the stiffness of aluminum and steel, gaining performance while preserving accessibility. The Replistruder 5 ranks highest in mechanical performance because it is optimized entirely around premium glass syringes and a narrow, high-quality configuration, which is precisely why it scores lower on versatility and affordability. The Enderstruder maximizes simplicity for a single popular printer, while the Large Volume Extruder accepts a resolution ceiling in exchange for large volumes of low-cost material. No prior tool, the analysis shows, occupies the center of the design space.

The Allstruder was engineered to do exactly that: remain broadly capable across all five metrics simultaneously, with particular attention to the simplicity and versatility gaps left by existing designs. Mechanically, it divides into four main sections. The actuator consists of a 3D-printed frame housing a leadscrew-driven pusher block guided along a precision linear rail, with the leadscrew supported by ball bearings at both ends for smooth, stable motion. Two frame sizes offer stroke lengths of 66 and 116 millimeters. The transmission, housed in a printed motor mount, uses a fiber-backed 2GT timing belt to couple a NEMA 14 or NEMA 17 stepper motor to the leadscrew, with slotted mounting holes allowing straightforward belt tensioning and backlash reduction. A keyed slot on the pusher block mates with a boss on each syringe adapter, guaranteeing correct realignment every time a syringe is swapped.

That adapter system is the heart of the device’s material and machine agnosticism. Paired printed adapters, one gripping the syringe plunger and one holding the barrel, allow the Allstruder to accept reusable gastight glass syringes from 0.1 to 25 mL and disposable plastic syringes from 3 to 100 mL, positioning each syringe as close as possible to the actuator to minimize deflection and positional error. The growing component ecosystem includes two frames, two motor mounts, two pusher blocks, twelve syringe adapters, a Bowden nozzle adapter, a syringe heater for materials like chocolate, and more than ten printer mounts. Three example configurations illustrate the range: a balanced base setup with a 2.5 mL glass syringe; a large-volume Bowden arrangement using a 50 mL syringe and extended frame, mounted to the printer frame with extrusion delivered through tubing; and an extreme-precision build pairing a 0.1 mL glass syringe with anti-backlash components and a 0.9-degree stepper motor for fine control of precious inks.

Physical design choices reflect the demands of high-speed, multi-material printing. Four widely spaced mounting bolts secure the extruder firmly to a printer’s gantry, and a deliberately low center of mass minimizes vibration and wobble from inertia during sharp directional changes, much like a wide-wheelbase racing car. The motor, the widest component, sets the overall width at roughly 44 millimeters, allowing multiple Allstruders to be arrayed densely for multi-material work or spaced apart for applications such as printing into petri dishes. The platform supports direct drive and Bowden-style setups, coaxial extrusion, high-pressure, high-resolution, and high-speed configurations. Assembly requires only metric Allen wrenches and standard bolts, proceeds largely in a single plane, and is documented in step-by-step video guides. Printed parts are optimized for PETG on standard FFF machines, refined through more than 85 iterations aimed at improving first-print success rates, with PCTG and certain photopolymer resins also validated.

Validation was conducted through a distributed network of laboratories using different materials, printers, and skill levels, with iterative feedback used to eliminate adoption-limiting issues. The device has been fitted to more than twelve popular printers and bioprinters, ranging from Creality Ender 3 V2 machines to a CellInk INKREDIBLE, and was adapted to the Printess, a low-cost open-source bioprinter from the Skylar-Scott lab, via a custom mount. Mechanically, a dial-indicator test pressurizing a 5 mL plastic syringe to 30 PSI above ambient, a pressure exceeding what most bioinks require, measured a maximum pusher deflection of just 20 micrometers at a calculated force of 24 newtons, quantifying the rigidity of the drive mechanism itself. In a representative print test on a Creality K1 SE using a 1 mL glass syringe, 23 mg/mL Type I collagen, and a 30-gauge needle, printed collagen filaments averaged 141.8 micrometers in width against a 150-micrometer needle, with center-to-center spacing errors below 3 percent and between-filament spacing errors under 4 percent, results the authors attribute largely to the host printer and syringe rather than the extruder.

Beyond printing, the team envisions the Allstruder as shared infrastructure with uses well beyond its original community. Researchers can move between embedded FRESH printing and direct ink writing across bioinks, hydrogels, ceramic and aerogel precursors, edible materials, conductive inks, and silicones on a single reconfigurable head. Hardware developers can treat it as a stable, well-characterized base for custom syringes, heaters, chillers, manifolds, active mixing heads, and valved dispensers. Labs with heterogeneous printer fleets can standardize on one extrusion platform, making protocols portable between machines and institutions. The actuator can even serve as a programmable, printer-controlled syringe pump for reagent metering or fabricating assay substrates such as immunochromatographic test strips, and it functions as a low-cost, openly documented linear stage for general precision-motion tasks. At roughly 50 dollars per unit, it has already been used in workshops worldwide where commercial syringe-extrusion systems would be cost-prohibitive, lowering the barrier to hands-on education in additive manufacturing and biofabrication.

The Allstruder’s release arrives amid growing calls for standardization in extrusion-based bioprinting, where round-robin studies have highlighted how difficult reproducibility remains across labs. By consolidating lessons from a decade of open-source extruder development into one adaptable, rigorously characterized platform, its creators hope to shift community effort away from reinventing actuation and toward the science the hardware enables. The device does not outperform a purpose-built tool within that tool’s own niche, the authors are careful to note, but it delivers strong performance while remaining easier to use and more broadly compatible, making it the more practical option for most users and applications. In that balance, a mechanism rigid enough that print fidelity is limited only by the user’s choice of syringe and printer, offered freely and inexpensively, the Allstruder aims to become the common foundation for the next generation of syringe-based printing.

Subject of Research: An open-source, low-cost syringe pump extruder enabling versatile fluid and biomaterial 3D printing on standard desktop printers.

Article Title: The Allstruder: an open syringe extruder for every 3D printer

Article References: Hinton, T., Patten, R., PereiraTavares, A. J., Crosby, C., & Shiwarski, D. J. (2026). The Allstruder: an open syringe extruder for every 3D printer. HardwareX, 28, Article e00827. https://doi.org/10.1016/j.ohx.2026.e00827

Image Credits: AI Generated

DOI: 10.1016/j.ohx.2026.e00827

Keywords: open-source hardware, syringe extruder, 3D bioprinting, FRESH printing, direct ink writing, bioinks, additive manufacturing, HardwareX, hydrogels, low-cost bioprinter, reproducibility, CERN OHL

Geoelectrical surveying works by injecting a controlled electric current into the ground through one pair of electrodes, labeled A and B, and measuring the resulting voltage with a second pair, M and N. Because different earth materials conduct electricity differently, the measured response reveals the spatial distribution of electrical resistivity beneath the surface. This simple principle underpins an astonishing range of applications: locating groundwater aquifers, tracking contamination plumes and landfill leachates, characterizing soil for civil engineering foundations, exploring for minerals, monitoring dams and levees, studying archaeological sites, and even watching dynamic subsurface processes unfold over time through electrical resistivity tomography. The technique is non-invasive, relatively fast, and, with the right instrumentation, remarkably precise.

The problem, the researchers argue, is that the right instrumentation has historically been expensive and closed. Commercial resistivity meters prioritize robustness and automation, but their proprietary electronics and firmware make it nearly impossible for scientists to modify the architecture or adapt it to unusual experimental needs. Open-hardware initiatives such as OhmPi have begun to change that landscape, demonstrating a growing appetite for accessible, reproducible, and customizable instruments. PRISM pushes this trend further by pairing an unusually high-resolution analog-to-digital converter with automatic polarity reversal and a modern browser-based control interface, all under permissive open-source licenses: GPL-3.0 for the software and CERN-OHL-S-2.0 for the hardware.

At the heart of the instrument sits the LTC2440, a 24-bit delta-sigma analog-to-digital converter chosen for its high resolution and low noise. In geoelectrical work, both the injected currents and the measured potential differences can be vanishingly small, so conversion resolution matters enormously. A 24-bit converter reduces quantization effects and allows the system to resolve fine variations in signal that a conventional 16-bit converter would blur into noise. To keep the conversion honest, the designers paired the ADC with an LT1236-5 precision voltage reference providing a stable 5.000 volts with minimal thermal drift, and they built a virtual ground circuit around an LTC2051 operational amplifier that shifts the signal’s DC level to 2.5 volts, allowing bipolar measurements in a single-supply system without violating the converter’s input limits.

The measurement chain continues with an LT1007 low-noise operational amplifier configured as a high-impedance voltage follower for the voltage coming from the ground, complete with a 10-kilohm multiturn potentiometer for offset compensation, and a resistive divider that can attenuate signals by a factor of five when excitation levels climb. Current is measured indirectly through a precision 22-ohm shunt resistor with a tolerance of just 0.1 percent, switched into the circuit by a relay only when needed to prevent parasitic effects. An Arduino Pro Micro board based on the ATmega32U4 microcontroller orchestrates everything, coordinating relay switching, ADC readout over SPI, and communication with the user’s computer at 115200 baud.

Perhaps the most elegant feature is the automatic polarity reversal mechanism. Every measurement point is sampled twice: once with current flowing in the forward direction and once in reverse. The voltage measured at the electrodes is the superposition of the true resistive response and the spontaneous potential that the ground naturally generates. When current flows one way, the measured voltage equals the response plus the spontaneous potential; reversed, it equals the response minus the spontaneous potential. Summing the two readings cancels the spurious component entirely, yielding twice the true resistive voltage. Crucially, the system reverses the polarity of the potential electrodes simultaneously with the current electrodes, guaranteeing that the final recorded value is always positive regardless of injection direction.

The team validated the instrument rigorously in the laboratory. Calibration curves were constructed for voltage and current using a Siglent SDM3055 digital multimeter as reference, a precision LT1021-based voltage source, and a Newport Model 505 laser diode current source, with linear regression coefficients of 0.9999 across all ranges. Statistical testing with 10,000 consecutive measurements of a 0.999091-volt reference produced a mean of 0.999139 volts, a standard deviation of just 2.57 microvolts, and an effective number of bits, or ENOB, of 19, meaning real-world noise degrades the nominal 24-bit resolution to a still-extraordinary 19 bits. Signals on the order of 100 microvolts sit comfortably above the noise floor, and the error distribution followed a clean Gaussian profile, confirming that fluctuations stem from random thermal noise rather than systematic drift.

The head-to-head comparison with commercial hardware is where the story becomes striking. Measuring precision resistors spanning 10 ohms to 68 kilohms under conditions mimicking field surveys, PRISM kept its maximum measurement error to just 0.95 percent, below the nominal 1 percent tolerance of the test resistors themselves, with a mean relative error of 0.39 percent. The commercial PASI MOD. 16GL-N, by contrast, stayed below 1 percent error only up to roughly 2200 ohms, then degraded progressively, reaching approximately 27 percent error at 68 kilohms. The researchers are careful to note that the advantage cannot be credited to the 24-bit converter alone; it emerges from the complete measurement chain, including the low-noise reference, analog conditioning, printed circuit board design, firmware, and polarity-reversal technique working in concert.

The operating envelope suits field practice well. The instrument measures bipolar voltages from 100 microvolts to 10 volts and currents from 100 microamps to 100 milliamps, the latter capped by the 2.5-volt ADC input limit across the 22-ohm shunt. Injected currents in typical geoelectrical surveys rarely exceed 100 milliamps, so the range covers practical conditions. The browser-based graphical user interface, built with HTML, CSS, and JavaScript and communicating through the Web Serial API, lets users configure Wenner, Schlumberger, or Dipole-Dipole electrode arrays, computes resistance, geometric factor, and apparent resistivity in real time, and exports data to CSV for inversion processing. The firmware even discards the first ADC conversion after each relay switch to avoid transient artifacts and waits for the soil’s electrical response to stabilize before sampling.

The authors are candid about limitations: the system is designed exclusively for direct-current resistivity and cannot perform AC impedance or induced polarization surveys, its acquisition speed favors precision over rapidity, and field validation under real survey conditions remains future work. Still, the implications extend well beyond geophysics. The same four-point probe architecture can characterize the resistivity of graphene and other two-dimensional materials, perovskite thin films, and thermoelectric compounds such as bismuth telluride. With complete design files, bills of materials, assembly instructions, and firmware hosted openly on the Open Science Framework, PRISM invites a global community of researchers, educators, and tinkerers to replicate, modify, and improve it. In a field where a single commercial instrument can cost as much as a car, a 360-dollar, 19-effective-bit, fully open alternative may prove to be one of the most consequential pieces of scientific hardware published this year.

Subject of Research: An open-source, high-resolution analog-to-digital converter-based data acquisition system for geoelectrical resistivity prospecting

Article Title: High-resolution analog-to-digital converter-based data acquisition system for geoelectrical prospecting

Article References: Jiménez, M. L., Ruiz, A. G., Martínez, P. P., & Navarro, J. Á. (2026). High-resolution analog-to-digital converter-based data acquisition system for geoelectrical prospecting. HardwareX, 28, Article e00837. https://doi.org/10.1016/j.ohx.2026.e00837

Image Credits: AI Generated

DOI: 10.1016/j.ohx.2026.e00837

Keywords: geoelectrical prospecting, electrical resistivity, open-source hardware, analog-to-digital converter, 24-bit ADC, PRISM instrument, subsurface imaging, resistivity meter, polarity reversal, HardwareX, low-cost instrumentation, electrical resistivity tomography

Writing in the open-access journal HardwareX, Bas Stijnen, Joseph Thompson, Ryan Paetzold, Eoghan Somers, and David McKeown present a fully open-source, camera-based trifilar pendulum system designed to measure the mass moment of inertia of CubeSat-class objects with impressive accuracy. The complete hardware and software package, from 3D-printed platform tiles to Python analysis code, is released under permissive licenses including CERN-OHL, CC-BY-4.0, and the MIT License, and the total cost ranges from roughly 55 euros for the bare pendulum platform to about 550 euros for a full setup with support frame and camera. The system has even earned open-source hardware certification under OSHWA UID IE000005, a formal stamp of reproducibility that few laboratory instruments can claim.

The trifilar pendulum itself is a beautifully simple piece of physics. A platform is hung from three equal-length wires and given a gentle twist. Because the platform’s centre of mass sits directly beneath the suspension point, it oscillates about the vertical axis with a period that depends on its rotational inertia, its mass, the suspension radius, and the length of the wires. The classical relation, derived under the assumptions of small-angle motion, rigid bodies, and negligible friction, links the measured oscillation period directly to the moment of inertia. What has traditionally made such setups expensive is not the pendulum but the instrumentation: precision rotary encoders or inertial sensors must be physically attached to the oscillating platform, adding mass, friction, and damping that corrupt the very quantity being measured.

The Dublin team’s key innovation is to remove contact entirely. Instead of sensors, they print two paper fiducial markers and tape them to the underside of the platform. These are not ordinary targets but N-fold markers, one with four-fold and one with five-fold rotational symmetry, selected using the MarkerLocator framework. The coprime symmetry orders allow the image-processing software to distinguish the two markers unambiguously and estimate rotational pose reliably from a single camera, even as the platform twists back and forth. A webcam or action camera mounted below the platform records the oscillation, and open-source Python software built on OpenCV, NumPy, and PyQt6 extracts the oscillation period, applies the trifilar equation, and reports the moment of inertia in kilogram metres squared, complete with an estimated measurement error.

The platform itself is assembled from nine triangular 3D-printed PLA tiles joined with brass threaded inserts and M4 screws, forming an equilateral triangular footprint roughly 407 millimetres on a side. The validated configuration handles test articles up to approximately two kilograms, a limit set not by the suspension hardware but by the stiffness of the printed platform, which can flex under concentrated loads and alter the effective suspension geometry. An optional support frame built from aluminium extrusion holds the pendulum and mounts the camera, making the system portable enough for ISO 8 CubeSat assembly cleanrooms, though the team found that suspending the platform directly from a rigid ceiling generally yields better results.

Validation was thorough and revealing. Using calibration masses with analytically known inertias, the researchers tested nine different moment of inertia values spanning from 0.15 to 6.1 times ten to the minus three kilogram metres squared, repeating every measurement five times. The results fell into three clear regimes. For inertias above three times ten to the minus three kilogram metres squared, errors stayed below five percent regardless of camera choice. In the intermediate range, errors ranged between five and fifteen percent, still acceptable for CubeSat characterisation. Below ten to the minus three, accuracy degraded sharply, sometimes exceeding forty percent with the support frame, because the inertia of the object becomes small compared with that of the platform itself, and the final answer emerges from subtracting two large, similar numbers.

Two practical findings stand out for anyone planning to build the system. First, the suspension material matters more than one might expect. Replacing steel cables with braided Dyneema fishing line, chosen for its negligible mass and bending stiffness, cut measurement errors dramatically, bringing even the lowest-inertia test case down to about 6.6 percent error. Second, camera quality matters mainly at the low end: a GoPro Hero 7 Black at fifty frames per second outperformed a basic Logitech C270 webcam by roughly ten percent for small inertias, thanks to better tracking resolution, while the two cameras performed nearly identically for larger objects. Camera distance, between fifteen and thirty centimetres below the platform, proved almost irrelevant, though the GoPro’s wide-angle fish-eye distortion introduced slight errors when markers drifted toward the frame edges.

The software also tackles a common experimental headache: imperfect centring. The trifilar equation assumes the test object’s centre of mass sits exactly over the platform centre, but real satellites are rarely so cooperative. The team implemented an optional correction based on the parallel axis theorem, subtracting the term mass times offset squared from the measured value. Verification tests with calibration masses displaced by five to twenty millimetres showed the software’s corrections matched theoretical predictions to within one part in a million of a kilogram metre squared. A free-decay experiment further confirmed that damping is negligible: the logarithmic decrement of 0.0162 corresponds to a damping ratio of just 0.00257, and the oscillation period shifted by only 0.38 percent over fifty seconds of decay.

The most convincing demonstration came with a representative CubeSat mock-up, an aluminium frame carrying four PCB-based solar panel simulators and integrated calibration masses. The pendulum measured a moment of inertia of 6.738 times ten to the minus three kilogram metres squared, within 3.7 percent of the CAD prediction of 6.996. The small discrepancy was attributed to exactly the kinds of details that make experimental measurement valuable in the first place: tape, fasteners, T-slot hardware, and assembly tolerances that no model captures perfectly. For university CubeSat programmes and small research groups, the message is clear. With a desktop 3D printer, a webcam, a kitchen scale, and freely downloadable design files and software, laboratory-grade mass property measurement is now within reach of virtually any team, and the era of guessing a satellite’s inertia may finally be drawing to a close.

Subject of Research: An open-source camera-based trifilar pendulum for measuring the mass moment of inertia of small satellites

Article Title: An open-source camera-based trifilar pendulum setup for measuring mass moment of inertia of small satellites

Article References: Stijnen, B., Thompson, J., Paetzold, R., Somers, E., & McKeown, D. (2026). An open-source camera-based trifilar pendulum setup for measuring mass moment of inertia of small satellites. HardwareX, Article e00821. https://doi.org/10.1016/j.ohx.2026.e00821

Image Credits: AI Generated

DOI: 10.1016/j.ohx.2026.e00821

Keywords: mass moment of inertia, trifilar pendulum, CubeSats, open-source hardware, fiducial markers, optical tracking, 3D printing, attitude control, small satellites, PocketQubes, HardwareX, low-cost instrumentation