Model Making How To: Transistor Driven Relay Switch

It seems every automation project we do here requires some type of low voltage, low current output to some type of higher voltage, higher current output. In our shop, this is usually the output of a Parallax Propeller chip to drive a relay. This allows us to switch just about any circuit we can dream up. Often we find ourselves turning to a very basic but essential circuit.

Parts List

D1     1N4002
Q1     2N2222
R1     390 ohm
RLY1   Radi
o Shack 275-240 

As you can see, the parts list is short and… here’s the best part… all of them can be found at your local RadioShack!

2N2222 Transistor with
the Emitter, Base and
Collector Labeled

390 ohm Resistor

1N4002 Diode and Schematic

5V Relay

More Information

Parallax has a great article on how to implement this circuit and how to use a ULN2803 darlington array.