Relay driver
Sometimes we just need to easily switch on and off an external load. Maybe the load is powered by AC current; maybe it's very high voltage that the Arduino can't handle. A transistor is usually used to power on such things; however, transistors are quite complicated. There is a simpler device that can just switch on or off, at slow speeds, an external load. This device is known as a relay.
Getting ready
To execute this recipe, we will need the following ingredients:
An Arduino board connected to a computer via USB
A general 5 V relay
A resistor between 220 ohm and 4700 ohm
A standard NPN transistor (BC547, 2N3904, N2222A, TIP120)
A standard diode (1N4148, 1N4001, 1N4007)
How to do it…
The relay coil unfortunately uses quite a lot of current. To prevent this from burning the Arduino pins, we will use a transistor driver to start the relay:
Connect one of the terminals of the relay coil to the 5V pin on the Arduino.
Check the data sheet of the transistor. We need to correctly identify the...
