Dr David Gibson
This page lists some of my more recent publications. Unfortunately, I cannot add them to the university's list because an honorary appointment does not confer access to Symplectic. So, here are some recent notes from the CREG journal. Click on the "CREGJ" links to go to the CREG Journal web site.
Position Encoder Uses Single-Track Gray Code: Part 1, CREGJ 116, p22-24. December 2021
There are many examples, in electronic equipment design, where it is necessary to measure linear or rotary position, which is often achieved using an optical or magnetic encoder. Simple encoders detect only changes in relative position; multi-track encoders can measure absolute position but, as David Gibson explains, a single-track encoder can, under the right conditions, also encode absolute position.
A Simple Class-D Single-Sideband Modulator, CREGJ 115, p10-13. September 2021
(part 2 in CREGJ 116, p20-21. December 2021)
David Gibson describes how the output pulses from two class-D double-sideband modulators using carrier-frequency PWM (CF-PWM) can be interleaved to create a class-D single-sideband modulation. The method, assumed to be novel, is simple enough to be implemented on a standard micro-controller, which means that it is more accessible to hobbyist designers than a DSP implementation.
Data Protocol and Coding Examples for the British Cave Science Centre, CREGJ 115, p16-20. September 2021
The British Cave Science Centre (BCSC) at Poole's Cavern in Derbyshire has been fitted with sensors and data loggers in support of a number of cave science projects. The sensors transmit their data to the Internet via a broadband telephone connection. Two data protocols are used, essentially a 'push' and a 'pull' operation, which David Gibson describes as 'Source-As-Browser' and 'Source-As-Server'. Each method has its advantages and disadvantages, which are explained in this article, that also gives examples of the code needed to handle the operations.
Update: Energy Harvesting, CREGJ 114, p10. June 2021
Further notes on energy harvesting and human-powered lighting by David Gibson.
The SSB Paradigm for Cave Radio is Outmoded - Is it Time to Move On?, CREGJ 114, p12-14. June 2021
If you want to build a cave radio that extends the art and doesnt just repeat earlier work, then David Gibson argues that SSB techniques are outmoded. Not only is DSB modulation simpler, but it offers additional opportunities - including receiving SSB signals, if that is still required. Expressly, Gibson suggests that trying to implement traditional analogue SSB methods on a DSP platform is without merit, because tailored DSP techniques (such as the CORDIC used in Graham Naylor's Système Nicola) will perform so much better.
Cave Radio antennas, CREGJ 114, p19. June 2021
In another of our 'Fundamentals' series, David Gibson explains why we use induction loops and grounded electrodes as cave radio antennas.
Update: (1) Battery Polarity Protector, (2) Pressurised Enclosures, CREGJ 113, p12. March 2021
(1) Further to his notes on building rugged equipment, David Gibson describes a simple addition to a battery connector that prevents cells being inserted in reverse. (2) As a follow-up to his notes on building rugged equipment, David Gibson further describes the use of a pressurised enclosure to prevent moisture ingress.
Energy Harvesting with Electrets, CREGJ 113, p16. March 2021
David Gibson envisages a portable energy-harvesting device utilising a wristwatch-style automatic winder, with the mainspring driving an electrical power generator that uses an electret material. The mainspring provides a method of regulating the power transfer, not unlike the concept of 'power matching'.
Update: Regenerative Brake, CREGJ 112, p21. December 2020
In an extension of his notes on regenerative braking, David Gibson describes how to build an LED lamp that is powered by a falling weight.
The Parallel-Fed Voltage Multiplier, CREGJ 111, pp10-12,22. September 2020
Voltage doublers and the Cockcroft-Walton voltage multiplier are examples of devices that use capacitors as charge-pumps to generate a high voltage at a low power in a relatively simple circuit. The conventional voltage multiplier is series-fed, acting as a 'bucket brigade' to pass the charge from one element to the next. This is difficult to analyse, as well as being inefficient, with a law of diminishing returns applying. A better scheme is the less well-known parallel-fed device, which has several advantages. David Gibson analyses this device, arguing that it deserves to be better known, and suggests some possible cave electronics applications.
The Mystery of the Missing Energy, CREGJ 111, pp20-22. September 2020
Whenever a capacitor is charged, energy seems to go missing. This has consequences when designing equipment that makes use of capacitor charging, such as a charge pump. David Gibson explains the phenomenon and challenges the reader to say where the supposedly missing energy might have gone.
Regenerative Brake Charges Your Caving Lamp Whilst You Abseil, CREGJ 110, pp13-16. June 2020
A caver abseiling down a pitch will lose potential energy, which is converted into heat in his abseiling device; but what if it were converted into useable energy instead? David Gibson explains the principles behind regenerative braking and how you might use the braking energy to charge a battery. However, this is for theoretical interest only, and definitely not something to try out in practice!