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Attention quartz movement experts: what kind of signaling is coming from the chip on a 7a28 to drive each of the 4 trains? Is it just pulsing the coil in an alternating polarity to ratchet it forward one tick? I'm familiar with larger unipolar steppers like you'd have on a 3D printer, but was curious how these operate with just two input wires. Presumably the only thing you could do is vary the polarity, so I'm guessing that's how it works?

If so, is there any special hardware needed to drive these, or is the chip just a microcontroller pulsing 1.55v in alternating directions once per second? I assume the amperages must be incredibly low for these to run for 2 years on a watch cell, and so there wouldn't be anything too exotic in there.

Thanks!
 
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