I needed to test some RC (radio-control) "analogue" servo motors.
As used in model boats, cars, aeroplanes etc
The circuit shown will achieve same.
There is a 3 connection input wiring.
Centre is ground, red wire is + 4.5 volt (I use +5V)
other remaining wire is a PWM (pulse width modulated) control signal.
From info' on the web it seems these servos respond to a pulse input
of about 0.5 to 2.5 millisecond at a 30 to 50Hz rate.
See diagram for further details
So far all the servo's test out OK