Homebrew PCBs

don't get fooled by the title.
the DS2761 chip has two voltage inputs, one resolves 15uV in +-32mV (direct
connection of thermocouple up to 500C) and the other resolves 4.8mV in 2-5V
range (good for a pot input). on top of this it measures it's own temperature
and has an i/o pin (plus a switch sensor).
the setup is very simple: the thermocouple goes to a screw terminal close to
the chip (isothermal) and the chip goes to one pin of the uC. the uC doesn't
even need a crystal, so the most expensive parts are the ref pot, the relay,
the power supply and other stuff you may add (LCD...), BTW all of this also
needed with an analog design.
the algorithm is also basically simple:
read the internal temp
read the uV input and scale to temp units
read the V input and scale to temp units
compare V to uV+T and make the on-off decision (the actual control algorithm)
set the relay accordingly
repeat once a second...

works like a charm, but I do only on/off (thermostat). an 'intelligent' control
algorithm is out of my scope as I have no (mathematical) control theory
background.
some smart procedure can be implemented to input the profile using switches for
command sequence and the pot for values if you want a stand-alone control w/o a
PC link.



--- Ross McKenzie <valusoft@...> wrote:
> If I am reading it correctly, the DS2761 is a "High-Precision Li+ 
> Battery Monitor". The datasheet says that its voltage measurement 
> channel does so with a resolution of 4.88 millivolts resolution. Typical 
> thermocouples have a resolution of around 40 to 50 microvolts per degree C.
> 
> So obviously I am missing something from your description below. Could 
> you elaborate please?


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