Robot Building for Beginners, Third Edition

CHAPTER 10 ■ LEDS

Setting Up a Multimeter for Diode Testing

1. On the multimeter, the black lead should be connected to the COM terminal.


2. The red lead is usually connected to W terminal, but you should check your
   multimeter’s manual.


3. Turn the multimeter dial to the diode symbol, which looks like an arrow crashing
   into a wall (see Figure 10-13). This indicates a component that allows electricity
   to flow in one direction (the arrow) but not the other direction (the wall). The
   diode setting is appropriate for LEDs, because the “D” in “LED” stands for diode.


4. Power up the meter and note what the display indicates. Some meters show “0L”
   or “OPEN” or something else to indicate that no electricity is currently passing
   between the probes.


5. Select an ordinary red LED. The color is important for this test.


6. Find the cathode lead of the LED. Usually that’s the shorter of the two wires, but
   check for a flat notch at the bottom of the LED lens to be sure. Connect the black
   probe to the LED’s cathode (-) and connect the red probe to the LED’s anode (+)
   (see Figure 10-14). It’s a lot easier if you use hook adaptors on the multimeter test
   probe tips. Don’t worry if you connect the LED in reverse. It’s not harmful.

Figure 10-13. Diode setting on multimeter dial