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Even a 6502 is overkill. Why not use a simple 8 pin device like this?
http://www.maxim-ic.com/quick_view2.cfm/qv_pk/2735
The only additional thing you'd need aside from a power source is a
transistor, a diode, and a relay. You can program the device with a
parallel port.
1) It doesn't appear to have an ability to enforce a minimum off-time. If
you repeatedly turn the compressor back on too soon after it has shut off,
that'll shorten its life. Choosing setpoints that are far-enough apart
might minimize this, but that would result in the temperature not being
as tightly-regulated as it could be.
2) It doesn't appear to have a way to slowly ramp the temperature up/down.
If the fridge is at 50 degrees and you want it to go up to 70 for a
diacetyl rest and then down to 35 for lagering, you want those
temperature changes to be made slowly (at a rate of maybe 1 degree per
hour).
These are things for which some sort of microprocessor control is needed. A
6502 might be overkill, but it's what I know, so there's less time getting
up to speed with an unfamiliar instruction set. I'm currently using DS18B20
sensors controlled by Apple IIs through a little bit of custom hardware, so
I already have software for the 6502 that talks to 1-Wire devices. Porting
that to another 6502-based machine would take minimal effort.
(If anyone's interested, the 1-Wire software is the first link at
http://alfter.us/a2soft.shtml.)
I also have the IIs graphing the temperature for the past ~4 hours; this
functionality would most likely go away, as it's (more or less) a curiosity
that was relatively easy to implement.
_/_
/ v \ Scott Alfter (remove the obvious to send mail)
(IIGS(
http://alfter.us/ Top-posting!
\_^_/ rm -rf /bin/laden >What's the most annoying thing on Usenet?
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