Everyone would have a digital multimeter these days. Even
the quite cheap ones have a huge range of measurements. All do the usual
voltage, current and resistance but many throw in continuity (often with a
buzzer), capacitance, transistor and diode checking, inductance, battery
checking and so on.
And when we say cheap, we mean it. You regularly see DMMs for
less than ten dollars; indeed one retailer, Altronics (who happen to have a
catalog in this issue) has even given DMMs away to customers when opening a new
So why would anyone want to build a project such as this which
simply measures one range of voltage and one range of current?
And just as importantly, probably costs as much (if not more than)
one of those many-function multimeters?
The idea for this project arose when we were "playing around"
with batteries and chargers (SILICON CHIP,
December 2006 and January 2007). Two of the things you must know, and know
instantly, when designing chargers and charging batteries are, of course,
current and voltage.
Even with several multimeters available (and used) I was always
swapping leads around, trying to work out which leads belonged to which meter
(Murphy’s law variation 1.3.3: multiple test leads, especially of the same
colour, will automatically tangle and lead to errors).