Servo Control Circuit

Justin - FLC

Hi,

I built a circuit that would take voltage as a signal to control a servo (0V turns the servo one direction, 10V turns the servo the other direction). I found the design for the circuit here: http://www.epanorama.net/circuits/servo10v.html. This circuit does exactly what it says it does which is to produce pulses ranging from 1ms - 2ms. Also, there is plenty of delay between pulses (~17ms)

When I apply this circuit to a 90 deg throw servo it works like a champ. However, when applied to the 180 deg throw servo (http://www.parallax.com/tabid/768/ProductID/101/Default.aspx) it does not. It will still only rotate 90 deg. I do not have much experience with servos, but the standard PWM seems simple enough and my control circuit should be working.


Any ideas???

Thanks,

Justin

W9GFO

It sounds normal. Most (probably all) servos respond to pulse widths outside of the 1mS - 2 mS range. You need to be careful of the limits, each servo will hit their stops at different values and if you try to force it you can strip gears.

The Parallax servo that I have requires a pulse width of .640 mS (PULSOUT 320) for full right and 2.350 mS (PULSOUT 1175) for full left.

You will need to scale your values to get a greater range of movement.

Rich H

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The Simple Servo Tester, a kit from Gadget Gangster.

Justin - FLC

Thanks for the reply!

I will try that. I was within the range of the specs on the servo, and I thought it was weird that it had exactly 90 deg throw. But your advice is greatly appreciated and worth a shot.

Justin

al1970

Hi:

It is most likely what W9GFO·said. But if that doesn't help, it also could be that you are not giving the servo enough time to get where it is going before you give it a command to move somewhere else.

Al

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Justin - FLC

Thanks for the input guys! Really nice to have support.

I will try widening and narrowing my pulses.

When I built this circuit I had an oscilloscope to test it, but now I am without. Any suggestions on testing my pulse width without the oscilloscope? Definitely important if stripping gears is a possibility.

Thanks!

Justin