....If you don't mind me asking,.. The heat source is a range-top "glass burner" I've characterized it's performance (with various heat setting & PCBs) with a multimeter thermocouple temp sensor. IOW, open-loop - So far results are satisfactory.. --=20 http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .