Simple Relay Control

I’m using the Pololu Serial Port 8-Servo controller. In addition to running my servo motors, I’d like to operate two relays from this controller. I want to keep this as simple as possible and was wondering if there is a circuit that could trigger a relay once the pulses get above x. Or is there an even simpler way to do this. Thanks.


Our recommendation would be to use a small microcontroller, which is getting to be the smallest and cheapest solution for many little circuits. That would make it easy to change thresholds or do things like close the relay for just a certain amount of time.

If you do not want to go with a microcontroller, you could try low-pass filtering the pulses with a resistor and capacitor and then putting that into a comparator. Such a circuit might take a bit of time to tune since the duty cycle change is not very large, and it might be a bit sluggish, too, since the pulse rate is low and you’ll have to go slow enough that that gets smoothed out.

We’ll add the individual high-low control feature to future revisions of our servo controllers since it should be easy to add.

- Jan