AC4XO Past Projects
From the 1960's through the 1990's, I produced a number of
hardware projects that are now only hazily remembered. Here's a
description of a few of them.
- RTL - As a lad in the '60's, I experimented with RTL (Resistor-
Transistor Logic). I built my own NOR gates from bipolar transistors.
At the time, transistors could be purchased cheaply by the pound,
so I acquired a number of units for my RTL experiments.
The problem with buying transistors by the pound is that they
are unmarked. So I built the No Guess Work transistor tester
("NGW Transistor Tester" by Don Lancaster,
December 1967) which allowed me to determine the type and relative
gain of the transistors I purchased.
- Remote Phone Ringer - When I was 12-ish, I build a circuit
that would detect the ring of a telephone and sound an outdoor
remote ringer. I did this long before the days of cell phones.
My parents would be working outside in the yard or garden, and I
thought a remote ringer would be useful.
I used an induction cup on the base of the phone to detect the ring.
This drove a transistor which closed a relay that rang a door bell.
- Capacitance Relay - For a seventh grade science fair project,
a friend and I built a one-tube capacitance relay. It was constructed
on a wooden board. The tube was a 25L6GT, and the 25 volt filament
voltage was provided by connecting the 120V main through a 25 watt
resistor. The circuit was connected to a square of aluminum foil.
When someone placed their hand near the foil, a relay would turn on
- Kits - I built a number of kits in the late 60's and early 70's.
Many were from
Popular Electronics articles where a third party, PAIA, provided
kits of parts. I built a drum machine
(Popular Electronics, February 1970 "The
Thumpa-Thumpa Box" by John S. Simonton, Jr.),
a wah-wah pedal
Popular Electronics, January 1970 "The Waa-Waa" by John
Stayton), and a guitar attach delay unit
Popular Electronics, June 1970 "Modify Your Electronic Guitar Sound"
by John S. Simonton, Jr.),
- Walter MIDI - In the 80's, I bought a Casio CZ-1 synthesizer and
wanted to control it using MIDI. Rather than buy a PC MIDI card,
I decided to build my own. MIDI uses a 31,250 baud current loop
interface. So if my PC had been capable of 31,250 baud RS-232, all
I would have needed was a serial to current loop interface. But IBM
AT-style computers of the day didn't support that baud rate.
So I built a PC MIDI interface with two UARTs. One UART ran 31,250
baud with a current loop interface while the second ran RS-232 at
38,400. The parallel data lines of the two UARTs were interconnected, and
handshake logic was provided to synchronize the data transfer between
the UARTs. On the PC side, hardware handshake was used to prevent
data overrun conditions.
The hardware worked very well, but the software for the project,
a DIY sequencer, was never completed. I was able to use the
system to capture CZ-1 patches.
A colleague named the project "Walter MIDI" after
- Benjy Toffer - The Benjy Toffer was a text-to-speech project
I built in the 1980's. It used a popular chip I bought from Radio
Shack that would translate phonemes into speech. I interfaced the
chip using a parallel interface that would connect to a PC parallel
interface and wrote a Basic program to drive the chip.
I called the project the "Benjy Talker" and tried to teach the unit
to say it's own name. But it kept saying "Benjy Toffer", so the name
There were other projects including a one-tube ham radio transmitter
and a CT7001-based clock. I designed, but never built, a simple
computer using the knowledge I obtained from reading
"Did You Ever Want Your Own Computer?" by Jim Huffman
November 1972 issue of 73 Magazine.
When I was very young, I read "Build a Computer" in the
January 1960 issue of
The "computer" in this article was a counter constructed from
flip-flops with a telephone dial for input and incandescent indicators
for output. But for 1960, this was a great article. It introduced
me to binary arithmetic and flip-flops. I never built the computer; however,
I did experiment with building a flip-flop. The transistors in the
flip-flops were 2N554 power transistors in TO-3 cases, so each flip-flip
was fairly large.