An Old Project

I have been messing about with electronic circuitry for almost four decades. I recently came across an early example of my work. The device is a digital event counter built around classic 74xx series logic. A chain of 74190 decade counters feed a set of 7447 decoder drivers and seven segment LED displays. A plastic project case with switches and connectors reminds me I have been building little devices for a very long time.

A Digital Event Counter
A digital event counter built when I was fifteen years old.
In some ways the unit is very similar to one of my more recent builds. Perfboard and point-to-point wiring are still standard construction techniques. The technology may have changed across the years, becoming far more complex, but some parts have remained the same.

Opening the little device up I inspect it… Things look serviceable inside, no signs of damage over the years. Curious I apply power and am greeted by red numerals. Connecting a signal generator has the numbers counting along happily. After decades in storage this old device of mine still works.

The workmanship in this example of my hand wiring is not that bad. Actually I would rate it acceptable, even by my current stringent standards. The layout is organized, the wiring reasonably neat, the solder joints perfectly serviceable. The fact that the counter still works after 35 years is testament to a well built device.

There are a few design choices I would grade poorly today. Apparently I thought a 1/8″ microphone jack was an acceptable power connector despite the fact it shorts the supply out briefly during insertion. Solid wire used for some of the connections to the front panel is also a poor choice. Three decades of experience has changed my standards.

A Digital Event Counter
Handwired perfboard and standard 74xx digital logic make up an event counter.
The technology used in the counter is interesting, particularly in retrospect. I have not used standard 74xx series TTL logic in many years, or even much TTL in general lately. In contrast the 7805 voltage regulator is still a staple part for me decades later, there is a small project in front of me at the computer right now, it features a 7805 regulator.

I have always loved the classic seven segment LED, seen here paired with 7447 decoder/driver IC’s. The red numerals have a nostalgia that I find very representative of so many circuits I have built across the years. While the seven segment has all but vanished from modern designs, replaced by LCD or even OLED displays, it was the standard numerical display of my electronic youth.

Author: Andrew

An electrical engineer, amateur astronomer, and diver, living and working on the island of Hawaiʻi.

Leave a Reply

Your email address will not be published. Required fields are marked *