CHAPTER 8 ■ CLIPS AND TEST LEADS- Turn the robot’s power off. Remove all of the batteries, if possible.
- Connect the black test probe of the multimeter to one piece of the robot. If you
prefer, you can use an alligator clip to connect the probe tip to the piece being
tested. Doing so is a lot easier than holding the black test probe in place. Also, a
hook clip may be able to reach spots that would be awkward for a test probe. - Touch the red test probe tip to each metal part throughout the robot, as
thoroughly as desired.
If an electrical connection exists between the part connected to the black test probe and the part being
touched by the red test probe, the meter will beep (or display “short” or a low ohm value or whatever). It
doesn’t matter how long or how complicated the connection is. If there’s an electrical connection between
the parts, the multimeter can detect it.
One of my line-following robots, Sweet, uses a metal candy container for a body. After drilling holes for
the sensors and screws (see Figure 8-12), I didn’t consider that cutting away the paint coating had exposed
the metal in the container to the robot’s circuits. When I proudly powered on the robot, the circuits went
crazy. Fortunately, I only lost a $15 chip that day.
I should have probed the robot a bit with the continuity mode of my multimeter before powering up. By
quickly checking the motors, each circuit board, major screws, battery connections, and body, I would have
noticed that direct electrical connections had mistakenly occurred between metal parts of the circuit board
and metal parts of the robot’s container.
Plumbing with Jumpers
In the last chapter, you learned that a 9 V battery works like an electricity pump. In this chapter, you learned
that alligator clip jumper wire (or any other piece of metal) acts as electrical pipe. All you need now is
something worth hooking up to the pipe.
Figure 8-12. Exposed metal on drill holes causes unintended electrical connections