# does anyone have a handy little circuit?

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!

Keshka

and use the isolator output to drive an op amp?

Why do you want an op amp?

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.

That doesn't make sense if the signal is at ground how can it source current? At a ground potential it can only sink current.

to a 90v motor control

then why has it got a 30V terminal?

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.

Keshka

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.

Lefty

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.

The drive manual can be found here: http://www.kbelectronics.com/manuals/kbmg_manual.pdf

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.

Keshka