PWM to RC servo pulse width

Thread Starter

Simon0362

Joined Sep 17, 2011
3
Hi All,

I have a pulse width problem that is bending my tiny brain at the moment - so if anyone can suggest some solutions I will be grateful...
The requirement is to convert electronically from a nominal 2-95% PWM duty cycle pulse width into a RC servo compatible pulse width (where 2% = 1ms servo pulse and 95% = 2ms). I can set the output frequency of the PWM pulse to more or less any frequency up into the KHz whereas the RC Servo frequency is at 50Hz.

I have built a 556 unit to manually produce the servo pulses and to change the pulse width, now I need to interface either that unit or an alternative solution with the output from the PC with it's much longer duty cycle.

I was going down the route of PWM output converted using a F-V followed by using that to adjust the control voltage of the pulse width part of the 556, but I wondered if anyone has a more elegant solution.
Just to make it clear, I am NOT interested in PIC or other ucontroller based solutions, this needs to be a pure hardware option.

Thanks in advance,
Simon
 

Thread Starter

Simon0362

Joined Sep 17, 2011
3
Hi MrChips,
because it is part of an embedded program that I have no control over - I can instruct it to send out the speed control signal between 2% and 95% of the maximum range but it will always be in this form - and not in the form that a RC servo expects (1-2ms on a 50Hz signal).

Simon
 

THE_RB

Joined Feb 11, 2008
5,438
...
I was going down the route of PWM output converted using a F-V followed by using that to adjust the control voltage of the pulse width part of the 556, but I wondered if anyone has a more elegant solution.
...
Well you ruled out the most "elegant" solution, the microcontroller.

Your idea of PWM->V converter to control an oscillator is pretty much the way to do it.

I would porbably use a dual comparator IC instead of a dual 555 timer as the comparator IC gives you easier control of the exact threshold setpoints where your oscillator will switch. It's a similar parts count; RC filter; 8pin dual comparator IC, and a few resistors and caps.
 
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