I have a cordless drill servo like this in the mill driving one axis:

cordless drill servo driving one axis

cordless drill servo driving one axis

The control board looks like this:

cordless drill servo control electronics

cordless drill servo control electronics

It’s based on attiny2313. The software has a safety function which halts all operations completely until reset if it can’t turn the motor for some reason (which means bad contacts to motor or sensor or jammed motor). The attiny seems to work on very small voltage, and i have two signal lines running from the pc parallel port to it. If it halted, it was still powered on from the parallel port and the halt status didn’t go away.

I figured i’d just enable the brown out reset function of the AVR so it would reset when i cut the main power from it. It did reset, but the brown out seemed to go active almost always when it drove the motor, which means it probably made the voltage waggle too much. Here’s what I’m trying as the solution to that:

the fix

the fix

That is, a diode to the input side of 7805 and an extra capacitor to ground from that side of the diode. Let’s see if it works…