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Step 7Add a Motor Driver
So far so good.
Only problem is that the motor doesn't seem to have all that much torque, which could be due to the fact that the microprocessor will only put out ~50mA per pin. The obvious next step would be to hook it up to a motor driver to supply it with more juice.
But then a little thinkin': I'm only driving it with 5v, and the coil-winding resistance is ~125 ohms. Which means that the motor's only drawing 40mA per pin, and it should be driven just fine by the (beefy!) AVR chip.
So to get more voltage driving the motor, I hooked it up to a SN754410 H-bridge chip. The circuit is pretty simple. Each pin from the AVR goes to an input, and the corresponding output pins go to the motor. The chip needs 5v for the logic section, and can take a lot more voltage in the motor section.
Running it on 11.25v (three 3.6v batteries) helped a bit. Noticeably more torque to my finger, but it's still not a powerhouse. Not bad for a motor which is smaller than a nickel, though. And now the circuit's become a general-purpose bipolar stepper motor driver.
Added Nov 29: Ran the motor last night at 12v for a while and it started to get hot. I'm not sure if it was a resonant frequency problem or if it was simply too much current for the windings. Either way, be a bit careful if you're driving this little motor with bigger voltages.
Only problem is that the motor doesn't seem to have all that much torque, which could be due to the fact that the microprocessor will only put out ~50mA per pin. The obvious next step would be to hook it up to a motor driver to supply it with more juice.
But then a little thinkin': I'm only driving it with 5v, and the coil-winding resistance is ~125 ohms. Which means that the motor's only drawing 40mA per pin, and it should be driven just fine by the (beefy!) AVR chip.
So to get more voltage driving the motor, I hooked it up to a SN754410 H-bridge chip. The circuit is pretty simple. Each pin from the AVR goes to an input, and the corresponding output pins go to the motor. The chip needs 5v for the logic section, and can take a lot more voltage in the motor section.
Running it on 11.25v (three 3.6v batteries) helped a bit. Noticeably more torque to my finger, but it's still not a powerhouse. Not bad for a motor which is smaller than a nickel, though. And now the circuit's become a general-purpose bipolar stepper motor driver.
Added Nov 29: Ran the motor last night at 12v for a while and it started to get hot. I'm not sure if it was a resonant frequency problem or if it was simply too much current for the windings. Either way, be a bit careful if you're driving this little motor with bigger voltages.
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If you're serious, you usually start off with an idea of how much torque and speed you need for your application, then find a motor that'll deliver, and then pick a motor driver depending on the motor's current requirements.
But for low-current applications, I've had good luck with the SN754410, for slightly larger currents the 293D is good, and above that, especially if you're driving with a microcontroller or need microstepping, Allegro has some great offerings.
And there's always build-it-yourself from 8 MOSFETs. Google for "H-bridge" to get an idea.
Enjoy!