Drive Relay with Servo Controller

[apg88]

I have a 4 port servo controller, two ports are being used by servos and I need the third one to drive a relay.

The servos work with a Pulse Modulated Signal, so I don't know if the relay will work with it.
I was thinking of using a capacitor to make the signal always-on when the pulses are going and turn of if there are none.
I'm not very good with electronics, so I don't really know where to put what and if it will work.

Thanks,

Alvaro

 

[dknguyen]

No, PWM will not work. But if you can use the controller to supply a 100% duty cycle PWM (and I mean absolutetely 100%) then it should work assuming the controller can provide enough current to power the relay (this is probably going to be the biggest problem if you are using a medium sized or larger relay). Personally, I don't think you really need a capacitor- you can just use code or whatever to make a 100% PWM pulse can't you. I don't think the cap would work the way you think it might either, because of the current demand- it's not just voltage a relay needs.

BTW put a diode in reverse parallel to your relay control terminals to protect the electronics against voltage spikes from turning the relay off (disconnecting power to the inductive magnetic coil). Reverse parallel- in the direction so doesn't short the PWM pulse across the relay control terminals but allows current to flow in a loop around the relay coil and diode.

Oh, if your PWM controller get's very VERY close to 100% but not quite, a capacitor too in parallel with the relay coil (like the diode, but make sure the polarity is the right way) should help that (in this case). It might help smooth out that very momentary dip that the PWM pulse might have even at 100% duty cycle. But if it's 100% you don't need it.

 

[apg88]

The problem is that the software I'm using will only do from around 500Hz to 1KHz. (I'm not sure exactly, but I think that's how it works 1ms-2ms pulses)

The relay I have says 5VDC at 89.3mA is nominal Current.

 

[audioguru]

You have a radio control system for a model car, boat or airplane.
The 1ms-2ms pulse will always be there. What do you want? 2ms to activate the relay then 1ms to turn it off?
A flip-flop circuit instead of the relay won't waste the high current in the relay's coil.

 

[mramos1]

Maybe google for d-type flip flop and see if that is what you are after. Is the output to trip it always the same and you want to flip it on and off?

 

[apg88]

You have a radio control system for a model car, boat or airplane.
The 1ms-2ms pulse will always be there. What do you want? 2ms to activate the relay then 1ms to turn it off?
A flip-flop circuit instead of the relay won't waste the high current in the relay's coil.

No, I can turn off the pulse if needed. So any pulse will be on and no pulse will be off. I will look into the flipflop...

I just found this: https://www.teamdelta.com/products/prod2.htm
It would be that, but way more simplified, no need for all the safety features.