As shown in Figure 8-1, the LED wiring is quite different from previous projects, because an electrical ground and a +5V battery are used to individually operate them. The idea behind this wiring technique is to allow one LED to be on at all times. The circuit schematic diagram in Figure 8-2 on the left shows LED1 on while LED2 is off. The DPDT (double pole, double throw) switch upper contacts are open with the bottom contacts closed. The closed contacts allow current from the battery (+5V) to flow through the LED (LED1) turning it on. The open contacts turn off LED2 because no battery current is flowing through it. The Arduino microcontroller will use this DPDT switching method for the Up-Down Sensor project to operate two LED orientation indicators.
Figure 8-2. Circuit schematic diagram for a DPDT switch toggling two LEDs
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