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, Popular Electronics 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 a light.

• 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.), among others.

• 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 Walter Mitty.

• 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 stuck.

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 in the November 1972 issue of 73 Magazine.

When I was very young, I read "Build a Computer" in the January 1960 issue of Electronics Illustrated. 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.