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555 circuit to generate a pwm signal to drive a servo using a 0-5v input

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treefiddy

New Member
Hello,

This time I need to find a circuit that will generate a pwm output signal that is able to drive a servo motor. The output signal needs to ve controlled from a 0-5v input. What I want is that that the servo will adjust its position depending on the input voltage to the circuit.

I want to control a variable geometry turbo and a servo has it's own positioning control so I just need to tell it where it needs to be. I'm using a pressure sensor that goes from 0 to 30 psi and the voltage output is from 0 to 5v.

Anyone has a good idea or a circuit schematic with parts list to accomplish this? Most 555 circuits that I find out there involve moving a variable potentiometer to adjust the servos position.
 

MikeMl

Well-Known Member
Most Helpful Member
What is the PWM frequency? How stable does it need to be?
 

cr0sh

Member
In theory, one of those 555 circuits should work fine - take this one, for instance:

R/C Central Article: Servo Driver

If you removed VR1, R3, and D2, then connected R2 directly to where the wiper was (pin 7 on the 555) - leaving everything else the same; then in theory the voltage change should effect the position of the servo (because all that VR1 is for is a voltage divider between the positive and negative rails - R3 and D2 - and R2 - are, I believe, just protection components).

At least - I think such a thing should work; hook a scope and/or servo to the output of the 555 (pin 3 after R4), and try it out - if the 555 dies, you haven't lost much...
 

MikeMl

Well-Known Member
Most Helpful Member
Crosh, the circuit you posted will produce the type of signal utilized in model airplane servos, which is not what the OP is looking for (I think)?
 
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cr0sh

Member
Crosh, the circuit you posted will produce the type of signal utilized in model airplane servos, which is not what the OP is looking for (I think)?
That's true; I am not sure what kind of "servo" he is working with - I thought it was either some kind of custom thing he put together on his turbo, or maybe it used such a servo...? I guess if he needed something else, then that circuit probably wouldn't work, so we need more info on what he is working with (maybe a spec/data sheet would help here!). It might be a good starting point, at least...
 

treefiddy

New Member
Actually the servos that I'm planing to use has a neutral position "mid travel" of 1.5ms so basically I need the same pwm used to control hobby servos. I don't know much about electronics, just basics and how to solder properly. Bellow are the specifications of the servo that I plan to use for now. Thanks for the help so far.

Heavy Duty Servo Actuators
 
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