This is an expansion on 0.02. It
closes the loop, feeding the temperature readings into the amplifiers.
It can both heat and cool. The circuit as is, is limited to about 300ma
of current at 12V, increase the current by reducing the value of the 10
ohm resistors. But be careful, the resistors will need ratings of at
LEAST one watt, and the power amplifier will need heavy heatsinking.