I am using an SN754410 to drive a bipolar stepper using the typical 4 pin setup. On a breadboard, it works fine. On the project board, it doesn't and overheats. The stepper rattles but does not respond to switches. This http://www.flickr.com/photos/50454200@N06/8595069215/ photo of the very poorly designed board will hopefully illustrate the problem. The Mega is powered by a 6v dc to dc converter from an 8amp, 12v power supply. The lower chip is an ULN2003 driving a unipolar stepper without a problem. I am hoping the photo will suffice. My schematics are amateurish as best.
I should have mentioned the breadboard was powered by a 12v, 500ma wall wort. Do I need a regulating circuit to feed this driver?
You need to tell us exactly which stepper motor - its current and resistance ratings and number of wires at least.
Sorry, the motor is rated at 10~12v, 259ma, 7.5 ohm., four wires.
I pulled the SN754410 and replaced it with a driver circuit https://solarbotics.com/product/k_cmd/ with the same result; even with a heat sink, it is going to fry. The motor is also running hot. I need the 8amp, 12v supply to run all the devices on this project (3 servos, three DC motors, two steppers, LED's, etc.). The steppers work with smaller wall worts, 12v - 500ma, but not the larger supply. Here is a rough drawinghttp://www.flickr.com/photos/92579016@N08/8601791760/. I am hoping there is a simple method of limiting the current from the power supply for these steppers? If not, is a separate power supply possible, using the same Mega?
ifugaopapercraft: Sorry, the motor is rated at 10~12v, 259ma, 7.5 ohm., four wires.
7.5 ohm at 260mA is about 2V, not 10 to 12, and given its 4-wire its likely to be designed for chopper-drive, so ignore the voltage rating and use the 0.26A as the per-phase current. A chopper drive like the A4988 is the recommended way to go, not an H-bridge, in that case.
But first measure the winding resistance to make sure it actually is 7.5ohm...
Sounds like quite a small motor at 0.5W static dissipation...
One way to avoid the need for a chopper-drive circuit is to use series resistance with the H-bridge. Since The SN754410 will lose at least 2V, we'll call the supply 10V which means a total of about 40 ohms is needed per winding, so 33 ohm loads in series with each winding will make it compatible with 12V H-bridge (but will dissipate 2W each - so use 3W rated power resistors). This technique is the "poor-person's" constant-current drive...