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Where can I find a source to buy lavet-style stepper motors?

Can I direct drive lavet-style stepper motors using the uC or do I need a driver IC?

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The problem is that if that eventual supplier stops selling lavet motors, the answers will become invalid and it makes these questions hard to mantain (as too localized) –  clabacchio Apr 24 '12 at 7:11
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@clabacchio - No, there is no single supplier of this motor. It's a type of motor used in watches. I think it's a perfectly good question. –  Rocketmagnet Apr 24 '12 at 12:21
    
@Rocketmagnet The problem is not if the supplier is single or not; shopping questions are discouraged as too localized and difficult to mantain up to date: meta.electronics.stackexchange.com/questions/375/… –  clabacchio Apr 24 '12 at 12:24

1 Answer 1

You'll need to consider how much current the motor takes, and compare it to the microcontroller's datasheet, which will state the maximum current draw on any pin.

Whatever you do, you'll also need to add a flyback diodes. When the MCU or driver attempts to change the current suddenly, the coil will generate back EMF (a possibly large voltage). Since you will be using current in both directions, you'll need 4 diodes.

Diodes Coil

My advice though would be to use an H-Bridge chip.

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Aren't Lavet type stepper motors unidirectional? –  m.Alin Apr 24 '12 at 14:45
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@m.Alin - yes, they are, but the coil current is bidirectional. –  Rocketmagnet Apr 24 '12 at 15:13
    
Turns out that you only need the flyback diodes to ground, not to Vcc. Also, if you're using a lavet stepper designed for 1.5 volts - like from a clock - and your microcontroller runs at a higher voltage - like 3.3 volts - you should add some series resistors (I use 100 ohms on each lead). –  nsayer Sep 4 at 4:44
    
@nsayer I understand why you would only need the flyback diodes to ground as long as the MCU continues to sink current on one pin when it stops sourcing it on the other, but why would you need more than one series resistor? –  Tut Sep 4 at 11:21
    
Because the voltage drop for the flyback diode exceeds the maximum negative voltage spec of the controller pin. The series resistor limits the resulting negative current flow during the time when the inductor is being drained. –  nsayer Sep 4 at 14:59

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