SPDT Switch: Interactive Contact Selection

A single-pole double-throw (SPDT) switch connects one common contact, COM, to either NC or NO. Here a 5 V supply feeds COM, and each output has its own 1 kΩ load to ground.

Try it

1. Click Run simulation.
2. Click SW1 on the schematic. The blade moves and the two voltage traces swap levels while the simulation continues.
3. Click SW1 again to return to the starting position.

What to look for

Switch position	VNC (blue)	VNO (red)
NC, initial position	About 5 V	About 0 V
NO, after one click	About 0 V	About 5 V

The selected load draws about 5 mA. The unselected load pulls its output toward ground. NC means normally closed and NO means normally open; these names refer to the initial position.

The model uses 100 µΩ for a closed contact and 100 MΩ for an open contact, so the unselected output has a small leakage voltage. Contact bounce and switching delay are not modeled.