[Opendispense] Latest additions

Harry McNally harrymc@ucc.gu.uwa.edu.au
Sun Aug 3 14:32:51 2003

On Sun, 3 Aug 2003 19:14:43 +0800 dagobah@ucc.gu.uwa.edu.au (Bernard Blackham) wrote:

> > What I can't work out (yet) is that there is another circuit that
> > uses an optoisolator (U24). This _appears_ to sense when the motor
> > voltage droops by extinguishing the opto led and allowing
> > PE1 (pin 18) to rise high.
> From what I make of it, I was under the impression it extinguishes the
> LED when the motor voltage gets too high (above 25.4ish volts)

I was thinking this way but I thought the only way that could happen
is if there is a back EMF when the drivers turn off but it occured to
me just now that it _may_ indicate that the motor 24V regulator has
fried (Q1) and the motors are being fed 24VUN(regulated). We should
measure the nominal 24VUN voltage to see if that is >25.4 volts.

> > So if you find anything sensing those two pins, it may be related
> > to motor overcurrent sensing. I am just puzzled why there are two
> > circuits sensing motor state in different ways.
> There's also another circuit attached to PE3 which puts the pin high if
> the 24VUN (unregulated?) drops below 20ish volts. Still tracking down
> where they're used. I think I'm currently on a roll with the coin mech :)

I think this may sense that mains power has been lost. The switch
mode regulator that provides 5 volts will hold up for a while as the
24VUN collapses so the micro may have time to finish any nonvolatile
RAM writes and maintain system sanity for when power returns. I
was chatting to Nick about using that for our own system preservation
on power fail.


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