Saturday, July 7, 2007

Basic Radio Control Encoder

This is just a simple multivibrator with one timing resistor selected by a CMOS Johnson counter. In this way the start of each pulse is determined by a different potentiometer. Each potentiometer should vary from 0 to 100K. Note that normal joysticks used for computers may be fitted with a linear 100K pot but provide only 60 degrees of the total 300 degrees of movement. This means that you should either fit a 500K pot or change the timing capacitors (10n) in the encoder circuit.
The ON pulse from the multivibrator should be about 300nS to 400nS in length and the OFF pulse should vary from 200nS to 1200nS. With this timing you should be able to drive almost any of the cheaper servo's (eg. Futaba, Horizon etc). The servo should give you a 180 degree movement for the full movement of the encoder pot. The 10K resistor in the encoder circuit prevents a zero-ohm pot stuffing the full supply voltage on the base of the transistor. The 300K resistor determines the length of the silence between each channel pulse-train. This period of silence should be about 4mS or more. The 4017 outputs 0 - 8 can be used to give you 9 independant proportional channels but the tenth is used to provide the silence between each channel pulse-train. I have only shown six channels in the drawings so output 7 must be used to reset the counter back to 0 again.

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