Page 239 - 15 Dangerously Mad Projects for the Evil Genius

214 15 Dangerously Mad Projects for the Evil Genius

■ Connect the negative lead of the meter to the Some meters also have diode and transistor test
more negative side. Note that if you get this the connections, which can be useful in finding and
wrong way around, a digital meter will just discarding transistors that have burned out.
indicate a negative current, but if you’ve
connected an analog meter the wrong way Oscilloscopes
around, it may damage it.
Oscilloscopes (Figure A-9) are an indispensable
■ In the case of an LED, the LED should still
tool for any kind of electronics design or test
light as brightly as before you put the meter
where you are looking at a signal that changes over
into the circuit, letting you read the current
time. They are a relatively expensive bit of
consumption.
equipment and there are various types. One of the
Another feature of a multimeter that is most cost-effective types does not have any display
sometimes useful is the continuity test feature. at all, but connects to your computer over USB. If
This will usually beep when the two test leads are you don’t want to risk blobs of solder on your
connected together. You can use this to test fuses laptop, or wait for it to boot up, then a dedicated
and so on, but also to test for accidental short oscilloscope is probably the answer for you.
circuits on a circuit board, or broken connections
Entire books have been written about using an
in a wire.
oscilloscope effectively, and since every
Resistance measurement is occasionally useful, oscilloscope is different, we will just cover the
particularly if you want to determine the resistance basics here.
of an unmarked resistor.

Figure A-9 Oscilloscope