7 - Switches in Parallel

 

S.P.S.T. switches can be connected in parallel (as shown in the diagram). In this circuit, the multimeter is again testing the voltage across the lamp. It shows us how the switches need to be positioned for the current to flow through the circuit and for the lamp to light up.

Switches in Parallel

The slider switches in this circuit "make " when they are put to the "1" position.

 

Click the parallel switches to find the required positions to make the lamp light.

 

An Example of Parallel Switching: A lighting control circuit in a car can make the interior lights turn on when any of the car's doors are opened.

For this to work, each door needs to operate its own switch. All the door's switches are then connected in parallel (as described above) and placed in the circuit with the lamp. If any door is opened and its switch "closes", then current is allowed to flow through the switch and the interior courtesy lights come on.

This is known as a simple "If /then" control system and requires the switches to be connected together in parallel.

Again we can write a logical statement to describe this. First we will call the four door switches: switch 1, switch 2, switch 3 and switch 4. We will say, when any switch is closed, it is in state "1" (and when it is open, it is in state "0").

Logic Statement

If switch 1, OR switch 2, OR switch 3, Or switch 4, are "1" then the interior light will turn on.

(Can you see how this differs from the switches connected in series in the last section).

More complicated logic processes can be added to the system to provide additional choice - such as the brightness, or period of time the interior lights will remain switched on. Special dedicated electronic components called "logic gates" can be used to give this greater level of control.

Nowadays this is usually made possible by the car's digital computer management systems.