A solenoid is basically a coil of wire (electro-magnet) with a plunger in the middle that moves quickly inwards when a voltage is applied to the coil.

Since a solenoid is an electromagnet, it produces EMF which can damage any electronic devices driving it. You must use a silicon diode D1 (1N4001 recommended) to absorb the EMF, connected in reverse bias. (in reverse).

Operating voltages range from 6 to 24 volts. Generally the higher the voltage, the more powerful the solenoid is.

A solenoid generally draws quite a large amount of current, from about 0.5 Amps up to 5Amps or more
Below are 2 recommended methods of driving them.

• A Darlington transistor Q1 is used as a driver.
• Must have diode protection across the solenoid.
• It is advisable to use a heatsink for the transistor as it could get hot.