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.
R1 390 ohm
RLY1 Radio 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
390 ohm Resistor
1N4002 Diode and Schematic
Parallax has a great article on how to implement this circuit and how to use a ULN2803 darlington array.