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I don't care for conjecture, which is all you're offering.
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That's USD 184.75, and she's in Oz, so it'd more likely be about USD
250 before she got the part in hand.
Plus, she's got an old fridge and if went belly-up shortly after
spending the money for the defroster she'd probably wind up with a new
fridge and a homeless new defroster.
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Yeah, sure you would...
Why not post a schematic and some code showing how you'd propose to
implement your wily scheme, and I'll do the same proposing a strictly
hardware solution?
Game on?
OK, changed my mind, let do digital.
Let start with perhaps 4 buttons. Two to change cycles per day and two
to change durations. Three bits driving 138 (one of eight) to
indicate cycles (eight cycles should be plenty). Another three bits
to indicate durations such as 5,7,10,15,20,25,30 minutes. I doubt we
really want to defrost beyond 30 minutes anyway. So far, we can do it
with 10 port pins and 16 LEDs.
Just a quick first draft:
char cycle[8] = {1,2,3,4,5,6,7};
char duration[8] = {5,7,10,15,20,25,30};
int c_idx;
int d_idx;
while(1)
{
if(port(c_up))
c_idx++;
if(port(c_dn))
c_idx--;
if(port(d_up))
d_idx++;
if(port(d_dn))
d_idx--;
defrost_on();
delay(d_idx);
defrost_off();
delay_hrs(24/cycle[c_idx]);
}
...