Glen's Stuff

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CONTENTS (Browser "back" button returns to this menu) :

Retro 8-bit computing
Pong central arcade
Test and measurement projects
Misc. projects
Analog computing experiments and projects
Boat anchor repair and restoration zone (a serviceman's log)
Design resources


A cryptic clue as to where I reside (not Austria).


Retro 8-bit computing

Tandy / RadioShack TRS-80 Model 1 clone

A fully-functional clone and improved ground-up hardware redesign of Tandy Corporation's famous home computer from 1977.
Realised entirely in current-production CMOS logic and using the Z80 microprocessor in its current guise - the Z84C.

Commodore PET-2001 clone

A fully-functional clone and improved ground-up hardware redesign of Commodore's first true personal/home computer.
Realised almost entirely in CMOS logic and using current-production versions of the 65xx-series CPU, PIA and VIA.

8-Bit "VGA" video graphics cards for retro computing

Three individual video card designs, built out of 74-series derivative CMOS logic. No CPLDs or FPGAs! The cards are specifically intended to be used with old-school computer systems (Z80, 6502, et al.) and have 5V TTL/CMOS, 8-bit microprocessor-compatible control interfaces.

Realised from differing combinations of 74LVC, 74AC, 74HC and 74HCT logic, the resolution and colour specifications of the three cards are:

Card A: 640 x 480 pixels, 16777216 (24-bit) colour.
Card B: 640 x 480 pixels, 64 (6-bit) colour.
Card C: 320 x 240 pixels, 64 (6-bit) colour.

A video graphics card adaptor for the TRS-80 microcomputer with Level II BASIC

This project is of two parts:

Hardware - a very simple interface in 74HC(T) logic designed to permit any of my three "VGA" video graphics cards to be fully addressed and controlled via the Expansion Interface Port of a vintage TRS-80 Model 1 microcomputer. Add dual-monitor support and high-resolution graphics to your 1970s era hardware!

Software - fast machine-code driver and video graphics drawing routines callable by BASIC. Specifically programmed for 16 KB Level II machines and packaged as a single object file, the routines load into the top 4 KB of RAM with the SYSTEM command and provide BASIC with a host of powerful drawing functions.

Digital Complex Sound Generator

Here is my take on a stereo sound synthesiser designed to give a voice to old 8-bit computers like the TRS-80 model 1. The four-voice sound generator circuit is a functionally enhanced work-alike of the long-obsolete SN76489 “Digital Complex Sound Generator” chip by Texas Instruments, implemented entirely in current-production 74HC(T) logic!

A stereo pair of sound generator boards, for a total of eight independent voices, are connected to the host microprocessor bus via an interface board sporting the required (dip-switch programmable) address decoding logic. The interface board also contains a master clock source for the sound generator boards.

An RS-232 line-printer interface for the TRS-80 model 1

This little unit provides a bi-directional serial line-printer port for the TRS-80 model 1.



Pong central arcade

Oscilloscope Pong for one or two players

A paddle-and-ball game that renders simple vector graphics on an oscilloscope screen, but with a twist - the circuitry is implemented entirely in discrete components, all soldered together “dead bug” style over a sheet of bare copper laminate.

Over 300 individual semiconductor devices!

Video Pong for one or two players

A little bit of craziness – a video display version of Pong implemented entirely in discrete component circuitry, soldered together “dead bug” style over a rather large sheet of lacquered copper laminate.

Some features:

  • P.A.L. composite colour video signal generation
  • One (practice) and two player modes
  • 1.5 digit on-screen digital score counters (first player to 19 wins)
  • Realistic synthesised percussive ball-thwacking sounds
  • Simulated stereo sound with auto-panning that tracks the ball
  • 431 bipolar transistors, 6 junction field-effect transistors & 826 silicon diodes


Test and measurement projects

A 13.8V, 7A switch-mode power supply with over-voltage protection.

Specifically designed to power radio transceiver equipment.

Less than 0.05% ripple and noise.

An ultra low noise measurement amplifier

A fixed gain, JFET-input amplifier for laboratory noise measurements.

Basic specifications:

  • An input-referred voltage noise of less than 300pV square-root-Hz
  • 60dB (x1000) gain
  • <0.1 Hz to > 1MHz bandwidth

A NAND gate-only frequency counter

A six-digit frequency counter with leading-zero suppression implemented entirely in NAND gate logic.

Complete I.C. complement:

  • 249 * 74HC00 quad NAND gate
  • 1 * 74HC132 quad NAND gate with schmitt-trigger inputs
  • 1 * 4011B quad NAND gate (used in analogue mode as the signal-input pre-amplifier)

A simple audio oscilloscope

An audio-bandwidth solid-state oscilloscope with a fully synchronised linear-sweep time base implemented with only six bipolar transistors and two silicon diodes!



Misc. projects

A prototype 2-inch C.R.T. composite video monitor

A prototype 2” C.R.T. composite video display monitor knocked up one rainy weekend.



Analog computing experiments and projects

GK-1 analog-hybrid computer system

A Fourier synthesis character generator

An alphanumeric display unit in which Fourier synthesis is used to construct the individual characters.

A three-dimensional projective unit

An analogue computing aid which maps objects defined in three dimensional Cartesian coordinates (x, y & z) to a two dimensional X-Y oscilloscope screen. The projection of the object is fully rotatable through 0-360 degrees on both the x and y axes of the object.

A magnetic deflection display unit

A Rössler attractor circuit

An electrical analogue of the famous Rössler attractor.

A hyperchaotic Rössler attractor circuit

An electrical analogue of the four-dimensional hyperchaotic Rössler attractor.

A Lorenz attractor circuit

An electrical analogue of the famous Lorenz attractor.

Sprott Systems Circuits

Electrical circuit analogues and oscilloscope display photos for chaotic Sprott Systems B through S.

A self-programming analog computer for chaotic Sprott systems

An analog computer designed and built to experimentally simulate chaotic Sprott Systems A through S.

Telefunken's bouncing ball in a box: an analog simulation

My implementation of Telefunken’s once famous analog computing demonstration problem.



Boat anchor repair and restoration zone (a serviceman's log)

Philips GM5650 oscilloscope repair



Design resources

My analog computing bookshelf

Books on this arcane art that I’ve collected, sourced mostly from on-line books sellers via Abebooks. If you have a passing interest in analog computing, here are some suggested titles to look for.

Coefficient tables for active filter design. High-pass, low-pass, 2-pole through 10-pole



A typical prototype assembly on the bench: