"David Billington" wrote in message
...
I bought a Cal Controls 9400 controller with RS232 interface so that I
could monitor the temperature remotely and set the characterisitic
(setpoints etc) remotely. Haven't completed all the software for setting
data but the monitoring is OK.

You must have lots of time to write the code for microcontrollers for
this sort of app or do it frequently and have lots of source handy. I
program for PC and PDAs in C and C++ so will do some of that but making
my own controller when you can buy them for £160 ($240 ish) with
multiple programs capability and multiple setpoint per program. I would
buy one of those a use the time on the rest of the project.


I haven't looked at the more recent temp controllers, who makes the
programmable ones in the price range you mentioned.

I saw some kiln controllers that are set up to fire to different cone
numbers, not what I want. I was thinking of using a PIC16F877, just add a
crystal and it has ram, flash memory, analog to digital, PWM, serial
communications, .... all for $6.50. A temperature control PID routine
wouldn't be that difficult in Basic or C. Add an op amp ($1) to amplify
the thermocouples and it should be in business. The PIC's will drive an LED
directly from their outputs, so a Solid State Relay would be able to be
driven directly, no additional $0.25 transistor needed. The compilers have
routines for writing to LCD displays, reading/writing RS-232, Reading
keypads, Reading/Writing external Flash memories, etc. For me, the
electronics is part of the hobby I want to make some knives even though I
can buy a knife at Wal-Mart for less than $10. I think I can make a better
knife than I can buy at Wal Mart and I think I can build a more suitable
heat treating controller than can be bought for $500. I can even buy a loaf
of bread cheaper than I can make one in my bread machine, but the home made
bread is a lot better than the Wal-Mart stuff.