This page lists some hardware posts, tools and projects I've created.

Feel free to adapt any of the open source designs here, bearing in mind that they come with absolutely no warranty, and should be treated as potentially dangerous given that I am not a chartered electrical engineer. That being said, if you do find any of these designs useful, please drop me an email so I can get a warm fuzzy feeling!

In addition to the designs below, I designed most of the Razorbill Instruments RP100 high voltage power supply and amplifier for use with their line of stress and strain cells. It has many cool features, including USB control via some software. Buy one!

High voltage stuff

In my work it's often required to use high voltages to drive capacitive actuators such as electro-optic modulators or electrostatic drives.

High voltage polarity switcher

This circuit is designed to flip the polarity of its input, controlled via a signal between ±10 VDC. The input can have up to ±1000 VDC per conductor. Have a look.

High voltage filter

This is a circuit which removes ripple and noise from a power supply up to around 400 V. It uses a "Maida-style" high voltage floating regulator, and is based on a design by Pete Millett, but using a different MOSFET and suitable for higher voltages.

High voltage amplifier

This is a quad-channel, low noise, 0 to ±375 V source/sink, high voltage amplifier for driving capacitive loads.

Mains electronics

Mains inrush current limiter

This is a draft design for an inrush current limiter capable of temporarily limiting 230 V at 25 A. It attempts to solve the problem of lack of available 25 A inrush current limiters in a form factor small enough to fit into the one place we can fit these in our electronics racks, and uses a number of cool tricks.

Mains waveform monitor

This circuit measures the lab mains waveform for data quality purposes.

Electronics for scientific experiments

The type of science we do at the AEI 10 m prototype typically requires high speed (large slews at hundreds of kHz or a new MHz, large bandwidths) and low noise electronics. Most devices ultimately involve reading signals from photodiodes, filtering them and applying them back to various actuators.

Homodyne quadrature interferometer fieldbox

This is a lab front-end for small interferometric sensors used in gravitational wave experiments to provide a stable bias voltage to, and readout photocurrent from, photodiodes. It provides filtering and whitening capabilities, digitally switchable with readback and diagnostic channels. Outputs are differential to allow transmission over long distances to data acquisition hardware.

BOSEM fieldbox

These are specialised circuits to drive "BOSEMs" used to sense and feed back to suspended test masses used in laser interferometers.

Contec digital input and output interfaces

These circuits map 32 electrically isolated, bipolar CMOS-compatible input or output channels to a Contec PIO-64/64L(PCI)H digital I/O card.

Negative impedance converter coil damper

This board super-charges the damping performance of so-called eddy current dampers used on suspended optics for gravitational wave interferometry experiments.

Magnetometer readout

This board lets undergraduates conducting the geomagnetic storm detection laboratory at the University of Glasgow observatory quickly understand and build a simple closed feedback loop with which to detect fluctuations in the Earth's magnetic field due to changes in solar activity.

Op-amp noise and parameter tester

...when I can find time to write about it.

Networked coil drivers using Arduinos

...when I can find time to write about it.

Hobby stuff

Various hardware I've made for fun.

Designs for woodwork and 3D printing

I've recently got into woodworking and 3D printing with my Anycubic Mega X, which forced me to brush up on my CAD skills. Here are some designs I've made with CadQuery and OpenSCAD.

Taransay RF module

This is a small, Arduino-compatible node for sending and receiving data wirelessly via RF. The range is spectacular for home applications: typically over 100 m, and the power consumption is minimal for most sensing applications, allowing for battery lives of years. I've used these devices to track weather data at my family's cottage for years with no issues.

Ethernet environment sensor

This is an ethernet connected dust, temperature, humidity, pressure and light sensor.

Point of load Raspberry Pi Zero power supply DC/DC converter

This circuit provides a DC supply to power a connected load (such as a Raspberry Pi) and attached peripherals. This is useful for applications where one needs to power a Pi (which needs 5 VDC) alongside some other device such as a 12 V relay, but where for practical reasons there should only be one supply (the higher voltage). The on-board switch mode chip converts the higher voltage down to 5 VDC for the attached Raspberry Pi, for which the board's header is fully compatible.

Automatic plant watering system

This page describes my automatic plant watering system. It's a valve controlled by a Raspberry Pi, with a systemd service and timer to control its operation.


Stuff that doesn't fit into the other categories...

Standard resistors

Resistors, capacitors, inductors and zener diodes come in standard values. There's a lot of logic behind the choices of these values. More information, along with lookup tables of series and parallel combinations of standard resistors, is provided here.

Resistor types

There are various different types of resistor, each with different appropriate uses. See this post for more information.