DIY Test Gear from 1981
We can’t get enough of [Bettina Neumryn’s] videos. If you haven’t seen her, she takes old electronics magazines, finds interesting projects, and builds them. If you remember these old projects, it is nostalgic, and if you don’t remember them, you can learn a lot about basic electronics and construction techniques. This installment (see below) is an Elektor digital voltmeter and frequency counter from late 1981.
As was common in those days, you could find the PCB layouts in the magazine. In this case, there were two boards. The schematic shows that a counter and display driver chip — a 74C928 — does most of the heavy lifting for the display and the counter.
It is easy to understand how the frequency counter works. You clip the input with a pair of diodes, amplify it a bit, square it with a Schmitt trigger, and then, possibly, prescale it using a divider. The voltmeter is a little trickier: it uses a voltage divider, an op amp, and a 555 to convert the voltage to a frequency.
Of course, finding the parts for an old project can be a challenge. A well-stocked junk drawer doesn’t hurt. A PCB etching setup helps, too.
We’ve looked at her magazine rebuilds before. If you ever get the urge to tackle a project like this, you can find all the grand old magazines online.
youtube.com/embed/glEPG5nC8J0?…