I am trying to interface my Mega to a 90v motor control. The motor control has three terminals for me.
-> +30
-> signal
-> ground
The signal draws zero current when it is at 15v.
it sinks 30ma of current when tied to +30
and it must source 30ma when tied to ground.
I must provide isolation between these three signals and the Arduino.
Could I drive some kind of opto isolator with one of the PWM outputs from the Mega and use the isolator output to drive an op amp? I do not have the skill to engineer something like this and any help would be greatly appreciated!
Mike,
1) I thought op-amp because they can source and sink current.
2) does it make more sense if you think of it as +15, signal and -15?
3) I am not controlling the 90v motor directly, I am using a four quadrant regenerative drive designed for this purpose. I need to interface to the drive.
It would be helpful if you could post a circuit of the drive device or a manual that might better explain it's control interface. Certainly with the proper interface circuit an Arduino could probably work with it, but details details details are needed for a proper answer or example.
I thought op-amp because they can source and sink current.
No they can't.
does it make more sense if you think of it as +15, signal and -15?
not really.
OK on point 3.
So what you are saying the signal out of the arduino needs to be at one of three levels. Ground, +15V and +30V and that the current capability has to be at least 30mA?
If so that can be achieved with a couple of transistors and two arduino outputs.
This is really a half H-bridge circuit.
As the potential on the signal pin moves tward the +15 terminal, the motor speed increases in the forward direction and as the signal pin moves tward the -15v terminal the motor speed increases in the reverse direction.
In the documentation KB also indicates using a 0-10v external source connected between a fourth pin I have not mentioned yet labeled "common" and the signal pin.
GM, thanks for the heads up on the op amp. No engineering skill = bad ideas! (grin)
As you can see from the documentation the drive was designed to be used with potentiometer. I placed the pot they provided on there and measured voltage and current. I was also hoping to power the "interface" circuitry with the potential on those pins and not have to add a seperate powersupply, this may not be possible.