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Old 09-18-2016, 05:29 PM   #2845 (permalink)
MPaulHolmes
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I think I figured out yesterday why the driver boards may have failed for Eclipse but not me, and also why the previous board, with the built-in resolver to encoder chip didn't work. Basically, I've always programmed the attiny (even the surface mount one) before soldering it in (I have a cool little thing that grabs surface mount legs so you can put one in, program, and then remove). I had thought programming in system wouldn't be a problem, but what i didn't think of was, when the attiny is unprogrammed, the 2 "outputs" are inputs by default, so the 6 drivers' 12 input pins are left floating, so they could be high or low. Well, if one is randomly high, and another is randomly low, the driver output will have a constant DC load of about 2.7Ohm at 24v!! Needless to say, the little chip 6amp driver would quietly fail in that case the first time you turn on the board to program the ATTiny.

I didnt' see that happen because I always programmed the attinys before soldering them (just sort of randomly, since I had programmed several and had them laying around).

The fix is to add a weak pull down resistor on the 2 ATTINY push pull pins to ground. LIke 47k or whatever. Then, all the drivers are off while the attiny gets programmed.
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