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rc servo control using pic 3.3v device

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Full Member level 6
Nov 29, 2010
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i am having a pic controller that runs in 3.3v. i must generate a 5v pwm signal to control a rc servo, for that i am using a bc 547 transistor with a base resistor of 2.2k connected to pic io, emitter pin i grounded and collector pin i connected a 2.2k pull up with 5v.
now i connected the collector to rc servo pwm pin. is this the correct method, my doubt is the 2.2k pull up is OK will the servo move are it will need ton tum pole output?

From your description, your single transistor is in common emitter configuration. It inverts signal polarity. You must send it through a second transistor, to deliver the proper signal to your servo.

There is a chance that one transistor can be sufficient, if you can make it work in common collector configuration. However the output voltage may be dropped by 0.6V. Then it is 4.3V and it may not be recognized by the servo.

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Or, simply cause your pic to deliver an inverted signal. Then a single transistor is fine in common emitter configuration.

What you have should be fine as regards providing workable logic levels to the servo, but as Brad says, your circuit will invert the signal.

As the servo drive signal is now "upside down" the servo will still not recognise your signal.
It may be easiest and require a fewest parts to do the logic inversion in software if that is possible.


Since it is a pic controller, that generates the signals, it is no problem to generate inverted signals.


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