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it and we cannot accept legal responsibility for it.
A number of projects and circuits published in Practical Electronics
employ voltages that can be lethal. You should not build, test,
modify or renovate any item of mains-powered equipment unless
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Volume 52. No. 7
July 2023
ISSN 2632 573X
Editorial
Check your meter
Last month, Julian Edgar wrote an excellent review of the EEVBlog
121GW multimeter. It’s a very nice product, but perhaps not one
all of us could afford. Nevertheless, we all need a meter of one
kind or another, and these days it is almost always going to be
a DVM (digital voltmeter), which despite its name will likely
include the ability to measure AC/DC currents and resistance.
(Capacitance, frequency and diode parameters are often part of the
mix too.)
So, perhaps you settle for a cheap DVM, or maybe pick up a nice
piece of equipment second hand. All seems to be fine, but at the
back of your mind you can’t help feel that ‘seems’ is not really the
kind of measurement certainty you need. When the meter displays
0.254V how do you know it’s telling the truth or just pointlessly
impressing you with spurious digits that might have nothing to do
with the actual voltage under test.
The answer to this problem is calibration, and this month we have
just the project to keep your meters – old, new, cheap or pricey
– on the path of honest, repeatable accuracy. The Multimeter
Checker/Calibrator is a neat, compact design that can help restore
your faith in measured values of AC/DC voltage and current,
plus it includes a 0.1%-tolerance resistor to check the ohmmeter
function on your meter.
A good DVM really is essential for all aspects of electronics, and
knowing it is displaying accurate readings should be at the heart of
your approach to all measurements.
Time for a ‘scope?
Once you have a well-calibrated DVM the very next piece of test
gear on your list is of course the oscilloscope – ‘scope for short.
The problem is there is a truly bewildering array of choices. To
help you navigate through the blizzard of options, this month’s
KickStart from Mike Tooley is a great overview of the types to
consider, including some suggestions for cheap but reliable
second-hand models. High-end scopes can be eye-wateringly
expensive, but the good news is you really don’t need to spend a
fortune. A perfectly useable scope can be had for £100 or less, so
don’t let cost put you off investing in this most flexible piece of
electronic test gear.
Matt Pulzer
Publisher
Transmitters/bugs/telephone equipment
We advise readers that certain items of radio transmitting and
telephone equipment which may be advertised in our pages
cannot be legally used in the UK. Readers should check the law
before buying any transmitting or telephone equipment, as a fine,
confiscation of equipment and/or imprisonment can result from
illegal use or ownership. The laws vary from country to country;
readers should check local laws.
Practical Electronics | July | 2023
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