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Basic Electronics » Powering a Stepper Motor

January 12, 2011
by il1019
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I recently purchased a stepper motor from a supply store. It operates at 6V or higher. I've figured out how to control it by messing around with a 9V battery, but I'm unable to make it move using my microcontroller since it only outputs 5V. I'm planning on powering the motor with 12V (since I'm using a PC power supply). I've come up with two designs to solve this problem.

  1. Use an op-amp to bring the voltage coming out of the microcontroller up to 12V.

  2. Find a transistor that will use a 12V power source and flip on a 5V signal from the microcontroller.

I will be using an H-Bridge setup (courtesy of Wikipedia) to switch the direction of the current and move the motor forward, so I'm going to need some transistors anyway. So my question is whether one of those two ideas is better or if I'm going down the wrong path entirely. I'm fairly new to electronics (CS major) so please be lenient if this sounds totally stupid.

January 12, 2011
by Rick_S
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An op-amp would not typically have the ability to power a stepper motor as far as I know. The H-bridge or a specific stepper motor driver would be your best bet.

Both H-Bridges and Stepper motor driver IC's have inputs that you could driver directly with the output pins of your microcontroller as well as have provision for the higher voltage input for your stepper. So you would have two supplies, the normal 5V supply you use for your nerdkit, and a secondary supply with whatever voltage and current requirement your stepper needs. Just make sure both supplies share a common ground to keep all potentials relative to the same zero point.

January 12, 2011
by mongo
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You need a driver circuit to boost the outputs to a stepper motor. H bridges work if they can handle the current but you need to be careful with the timing.

Most steppers I have worked with have four coils and they are all tied to a common line, so there are 5 wires. A simple transistor output will do just as well. One for each wire.

January 12, 2011
by Rick_S
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I've used the L298's and they work very well. They will handle up to 46 volts at 4 amps (with proper heat sink). Combined with a L297, they drive steppers quite effectively. I've also used transistors to drive them which work equally as well, just require a bit more programming.

Rick

January 31, 2011
by il1019
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Thanks for your help! I ended up purchasing some L298s from Jameco. However I'm unable to get the to function as I would expect. It seems like I should be able to power these directly from my mc, but I'm not seeing what I would expect. I am able to successfully light LEDs with the L298 but it seems like I'm getting very low current across as the LEDs are barely bright enough to see light up - I had to turn off the lights to see they were actually going on and off properly! I have two inputs wired to my mc, the enable line held high (5V) and VSS power hooked up to my 5V and VS on a 12V power supply. Is there more to it than that? I was hoping to do the work of the controller myself (just to get a better understand of what's going on). Maybe I thought I could do too much :)

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