CHAPTER 8 ■ CLIPS AND TEST LEADS
A meter with continuity should now display short (see Figure 8-10) and should beep annoyingly. Some
meters display “0 mV” instead of the word “short.” Check your meter manual.
If you don’t have a continuity feature, the meter should display zero W (ohms) or a very small number.
Ever heard of a “short-circuit?” Well, this one is pretty short. The electricity from the meter goes out of
one probe and then directly into the other!
Experiment with the ohm ranges and the continuity setting of your meter. You want to get a good sense
for what the meter displays when there is a connection and what it displays when there isn’t a connection.
Testing an Alligator Connection (Shorted)
- Instead of touching the multimeter probe tips together directly, connect them
with an alligator jumper lead (see Figure 8-11). Using a single jumper, attach one
alligator clip to the tip of the black probe and the other alligator clip to the tip of
the red probe.
You should get the same value displayed on your meter whether you touch the probe tips together
directly or whether you connect them with a jumper. The alligator clips and wire are just as good at allowing
electricity to flow through them as touching the probes together directly.
During use, alligator clips may become loose or grimy and fail to make a solid connection. The wire
between the clips may rip and detach. In those cases, if the jumper lead no longer conducts a continuous
connection, you can test for it on your multimeter. A broken connection will read “open” or some ohm value
greater than touching the probe tips together.
Think of the wire in the alligator jumper lead as electrical pipe. Electricity flows through the copper wire
(or any metal) like water flowing through a pipe. Unlike water pipes, if you disconnect one end of the wire,
the electricity doesn’t spill all over.
Discovering Unintended Connections
The continuity mode (and also the ohm mode) of a multimeter has a very beneficial use in robotics. It
can detect if an unintentional electrical connection exists between various robot body parts and circuits.
Although you won't perform these steps now, here are some example steps you might take to test a robot.
Figure 8-11. Making a connection with alligator jumper leads