This "Beginner / Top Tenner" project is part of a short collection of projects, some useful, some instructive and some amusing.

This, our fourth Top Tenner (beginner’s) project, is an add-on unit for your multimeter, and works equally well if it is an analogue or digital type. As the name suggests, its function is to sample a changing voltage and hold it to give you time to read its value.

Reading a changing voltage can be difficult with a digital meter, because the final two or three figures of the reading may be changing too fast to be seen. There is the added complication that a reading of a digital meter is itself a sample-and-hold measurement. The meter samples the input voltage, then holds it while the analogue-to-digital converter in the meter converts the reading to digital form. Typically, the meter takes several samples per second so it is not possible to read each sample individually. We can only read a value when it is reasonably steady, perhaps varying only in the least significant digit.

An analogue meter is possibly easier to read with a rapidly changing voltage, because the eye can average out the changes over a small interval of time. There is also the inertia of the needle and coil unit to help steady the readings. Whether you have a digital or analogue meter, there are occasions when you will want to sample and read the voltage at a precise instant, or to sample it and read it at regular intervals of time. This project helps you do just this.