June 2020 Quiz SOLUTION

Since June has drawn to a close, here is the solution to the mystery circuit quiz:


As a few of you correctly guessed or deduced, the mystery circuit is the repeater controller for the club’s 146.91 MHz repeater (now VE2RWI). The circuit was custom designed and hand-built circa 1990 by Mark Morin VA2MM and Mark Hillier (then VE2HVW) from parts on-hand. The repeater we were using was a recycled Motorola “Community Repeater” but it did not have many features common to amateur repeaters. So, we designed and built our own controller from scratch and interfaced it to the repeater. 

The controller functions are:

  • Programmable (via EPROM) periodic Morse Code ID 
  • Transmit a brief courtesy tone (beep) on receiver squelch release
  • Adjustable Timeout timer
  • Repeater PTT control logic

What is unusual about this controller is that it does not contain any micro-controller or microprocessor chip. Building a repeater controller with TTL logic would be unheard of today, and it was probably foolhardy even at the time. But it did work and well enough to serve for many years.

The  three 555 were for:

  1. logic clock
  2. audio tone generator
  3. Time-out timer (if my memory serves)

Memory refresher: June 2020 Quiz:

You may have noticed a photo of this circuit in the photo gallery captioned “A piece of WIARC History”. This month’s quiz is to guess what it is, approximately when was it built, what it did, and any other information that you may devine. I suspect not very many current members know the answer, so we will also accept humorous wrong answers (specify “wrong answer”) and we will publish any funny wrong answers. Of course if you think you know the actual right answer, go for it!

This is a home-brew circuit (both in design and construction) by WIARC members at the time, as part of a larger club project. Here is a close-up shot of the component side of the board and a list of all active components on the board:

Mystery circuit

Active Component List:

Qty                 Part Number         Description
1                      MM2716                 16 kbit UV Erasable PROM
4                     74LS00                   Quad 2-Input NAND Gate
1                      74LS76                   Dual JK Flip-Flop
1                      74LS77                   4-Bit D Latch
2                     7493                        4-Bit Binary Ripple Counter
3                     LM555                    Timer IC
4                     2N3904                  General Purpose NPN Silicon Transistor
1                     1N4001                   General Purpose Silicon Rectifier Diode
3                    1N914 ?                    Small Signal Switching Diodes

In addition to the above active components, there are many resistors and capacitors, 2 variable resistors and two momentary push-button switches and one LED mounted on the front panel of the device. The circuit is coated in a generous layer of dust. The circuit appears to be designed to plug into a card-cage chassis through a 22-pin connector on the back of the board. Construction is a combination of wire-wrap for IC sockets and point-to-point soldering between feed-though discrete components. 

Congratulations for the following correct answers:

  1. Rick VE7RY
  2. Jan VE2JL

Funny wrong answers were also received:

  1. Mark VA2MM:
    Automatic license examiner. Press the button on the front. If the LED lights up, you pass. If not, too bad.
  2. Wayne VE2WRH
    Breathalyzer, mounted inside driver’s door. If alcohol level is too high when starting engine, car explodes.