2 1/2 digit DVM

ZS digit DVM elektor february 1981 — 2-33 Building a digital voltmeter is so simple nowadays that there is really nothing to it. All it takes are a couple of ICs which incorporate the entire circuit: A/D converter, counter and display control, so that a display will usually be enough to complete the job. The advantages speak for themselves: the circuit is easy to build, requires little calibrating and is fairly accurate. Unfor- tunately, however, all this is outweighed by one major disadvantage — try obtain- ing the prescribed ICs at your local dealer"s and you"ll find he won"t have them in stock. In other words, the hobbyist ends up not constructing a voltmeter at all. To make it more worthwhile, our designers racked their brains to come up with a solution using "ordinary" parts. The result? A 21/2 digit voltmeter with a very reasonable accuracy of ± 0.5%. It is sufficiently accurate for all the nor- mal chores, especially considering that the accuracy of a decent analogue m...