Profile

Dr David Gibson

Recent Publications

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.

Page last updated on 19-Jun-2023

Comparing Loop and Line Antennas for Cave Radio Applications – 1, CREGJ 122, pp14-16. June 2023

An induction-loop transmitter can operate at a higher current than a grounded electric dipole because the loop has a relatively low resistance when compared to the resistance between two earthed electrodes. However, the magnetic field from a loop falls off more rapidly with distance, so it is not straightforward to say that one antenna is better than the other. Several other factors, both physical and practical, come into play. In this article, David Gibson outlines how we might go about making a comparison. This is a nonmathematical article – a more complete treatment will be given in part 2 of this article.

Current Problems in Cave Radio, CREGJ 121, pp11. March 2023

Although through-rock radio is now well established, there are a number of puzzles that David Gibson asserts would benefit from further study.

The Circle of Least Confusion, CREGJ 118, pp16-17 + appendix. June 2022

David Gibson describes a term in optics and photography that is used to derive the range of distances – the depth of field – over which a subject remains in good focus. This does not, of itself, require restating here, although there are some circumstances, such as the construction of stereoscopic and stacked-focus images, where a recap is useful. Additionally, there is a modification to the standard formula that extends its use to small-format digital cameras.

Applications of Chain Codes for Position Encoders, CREGJ 117, pp16-18 + online demo. March 2022

Linear and rotary position encoders can measure position using a single-track binary sequence known as a chain code. In a follow-up to his article in CREGJ 116, David Gibson gives some further explanation of how chain codes can be used.

Underground 'Radio' Powered by Compressed Air, (Letter to the Editor), CREGJ 117, p21. March 2022

Viewing Poster-Sized Stereo Pairs, CREGJ 117, p22-24&1. March 2022
(also see update in CREGJ 119, p20)

Stereoscopic pairs are traditionally viewed using a handheld 3D viewer. But when printed in a magazine or shown on a display board, such images are difficult to view unaided, as well as being necessarily very small because the centrelines of the images must match that of the eye. For stereo pairs to have an impact, they must be larger, but a traditional method of viewing larger images requires them to be printed in false colours, thus making them impossible to appreciate without special tinted glasses. In this article, David Gibson describes a simple technique that avoids this problem and allows poster-sized full-colour photos to be viewed without any artificial aid. Significantly, this allows them to be fully-appreciated both as flat images and as stereo pairs.

Position Encoder Uses Single-Track Gray Code: Part 1, CREGJ 116, p22-24. December 2021
(also see part 2 in CREGJ 118, pp19-22, and further update in CREGJ 119, pp19)

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
(also see 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!