Glen's Stuff

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.

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.

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.

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.

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.

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

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!

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

Specifically designed to power radio transceiver equipment.

Less than 0.05% ripple and noise.

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 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)

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

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

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

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.

An electrical analogue of the famous Rössler attractor.

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

An electrical analogue of the famous Lorenz attractor.

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

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

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

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.