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Author Topic: PWM speed controller, opto coupling, and torque questions  (Read 712 times)
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Hey guys,

I want to control a zen spindle dc motor, 50 -100 watt motor, 32 volt psu, draws around 1 -2 amps.

I want to control the speed of this motor from 24 - 32 volts, which roughly translates to 5000 - 8000 RPM

I'm using my microcontroller to drive a series of stepper drivers(pololou drivers) these are attached to a 24v psu, and their grounds and the micro grounds are all attached.  The microcontroller also sends a pwm signal to canakit motor controller, pulsing the enable line. 

http://www.sparkfun.com/products/9670

okay, lack of electronics knowledge incoming, treat me as a child, I'm afraid to hook this motor controller and power supply and ground back to my micro controller because of the possibility of ground loops, I don't know, it doesn't feel right to have both psu's attached to the microcontroller thats hooked the my computer... fear...

so I wanted to optoisolate it, I bought this board here: http://www.sparkfun.com/products/9118

I'm not sure how to use this, if it will work, or if it is needed or actually harmful?
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okay, lack of electronics knowledge incoming, treat me as a child, I'm afraid to hook this motor controller and power supply and ground back to my micro controller because of the possibility of ground loops, I don't know, it doesn't feel right to have both psu's attached to the microcontroller thats hooked the my computer... fear...

Ground loops can cause low level noise that can cause problems like hum in audio amplifiers, or small jumpy low bit variation in sensitive A/D converters. You should have no fear wiring up common ground wires between your arduino ground and the negative terminal of your 32vdc supply. It would be a good idea for the ground wire between the PSU negative and the arduino ground pin be a dedicated wire, not shared with higher current ground wire needed to be run to the controller board.

Nothing wrong with using an opto-coupler, but it adds complexity and costs and unless your working from a proven schematic drawing your sure to have some problems getting to all work correctly.

Lefty
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hey guys,

I think I have a similar question. Is this about linking the ground of the stepper supply to the arduino ground (I'm a complete noob, so I might be mistaking)?

I'm currently wiring up a stepper with a L293d dual H-bridge ic to my arduino mega (http://www.arduino.cc/en/Reference/StepperBipolarCircuit). There are four ground pins that could be either a 5v ground to close the microcontroller circuit or a 24v ground to close the psu circuit.

Do I connect both ground wires to both the arduino GND-pin and the psu ground? Can you help me with this?
thanks in advance.

cheers, tim


   
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Ground them all to the PSU, If you have problems arising , draw your circuit for us.
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