Thermal control hardware can be simplified if you have a micro in the system... Use a DS18S20 or similar temp sensor (takes one I/O pin) and a software-controlled heater (one more I/O pin). The heater can be a cheap power transistor in a constant-current circuit (with another small transistor). With some attention in software to thermal delay, etc., you can get excellent results with this approach. A PWM generator can "linearize" heater response... Mike Hardwick, for Decade Engineering -- Manufacturer of the famous BOB-II Serial Video Text Display Module! -- http://www.piclist.com hint: To leave the PICList mailto:piclist-unsubscribe-request@mitvma.mit.edu