There is some info on implementing the temperature controller in the comments
at the start of the file heather.cpp
You can use something the simple single ended transistor driver that Warren
described or use a DC solid state relay. The program can manipulate two of the
RS-232 port control signals (one for enable and the other for heat/cool). The
simplest implementation uses just the heat/cool signal for controlling the fan.
Heating uses self-heating of the Tbolt. Cooling uses the fan to add room air.
I use a DC solid state relay with one end driven by the heat/cool signal and
the other by the enable signal. I have a current limiting resistor and a zener
diode across the relay to prevent overdriving the device.
The TT command sets the control temperature and enables the PID with default
parameters. The KA command does an auto-tune procedure to fine tune the PID
parameters. You can also individually change the PID parameters using various
K commands. Once you have a set if parameters that works well, you can
specify them on the command line (or in a configuration or keyboard script file)
When using a fan, you should set the control temperature somewhere between the
maximum room temp seen and the no-fan-on self-heating temperature of the unit
in the box.
And there are rumors of a list member volunteering to write a Heather manual...
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