A DPDT (double-pole, double-throw) switch is used to operate two different devices independently. Generally, the switch has six terminals, and the middle two are used to connect something that both devices will use, such as a battery. For example, the positive and negative terminals of a battery can be connected to the two middle terminals. A green LED (with resistor) can be connected to one set of terminals on one end, and a red LED (with resistor) can be connected to the two terminals on the opposite end. When the switch is moved to one position, the red LED lights. When it is moved to the other position, the green LED lights.
Place the 7805 regulator into the breadboard, noting which terminals are Input, Output and Ground.
Place the DPDT switch in the breadboard, connecting one centre terminal to the Output pin of the 7805 and the other centre terminal to the Ground pin of the 7805. It may help to solder connecting wires to the switch terminals before placing the switch in the breadboard.
Connect the longer leg (anode) of the red LED to one end terminal of the switch, along the side where the 7805 Output is connected. Connect the green LED in the same way on the opposite end of the switch.
Connect one leg of a 330 ohm resistor to the shorter leg (cathode) of the red LED. Connect the other leg of the resistor to the end terminal of the switch, along the side where the 7805 Ground is connected. Do the same with another resistor and the green LED on the opposite end of the switch.
Connect the red wire of the 9-volt battery clip to the 7805 Input pin. Connect the black wire of the clip to the 7805 Ground pin.
Connect the 9-volt battery to the clip. One LED should light. Slide the switch to the other position. The first LED should turn off and the other LED should light.
- If something doesn't light, check your connections on the switch. The terminals along the sides are connected, but the terminals are not connected across the switch.
- It is possible to have six different things connected to the DPDT switch, allowing two sets of four things to happen for each position of the switch.
- This is only one wiring configuration of the DPDT switch. Other configurations are possible.
- Always take safety precautions when soldering. Use safety goggles, wear proper clothing, ensure proper ventilation and never leave the iron unattended.
- If an LED glows a different colour or becomes hot to the touch, disconnect power immediately and check your connections. If the 7805 becomes hot, do the same.