A servo tester is useful to check the function of a servo or other circuits for the radio control system without using the transmitter and receiver of a radio control system.

Signals of the Remote System
Usually all radio control systems now work with positive pulses (Graupner, Futaba, Simprop...). Differences are only in connectors. The connected circuit (servo motor, electronical switch) receives the control information by the length of the pulses. During standby (joy stick in center position) the pulses have length of about 1.5ms. Turning the joy stick to one direction the pulse length will reduce to 1.0ms. In the other direction the pulse width will increase to 2.0ms. Depending on the used radio control system the pulses are repeated every 25 to 30ms.

Functional Description
With the integrated circuits NE555 a timer is built to create a pulse about every 30ms. The length of the pulse is adjustable with the potntiometer from 1ms to 2ms. The power supply for this circuit should not be higher than 5V, because of the maximum voltage for the connected servos or other connected circuits.

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