Design and prototype power circuit that have the following features:
1) Regulate power by way of adjusting the duty cycle by using triacs firing at zero crossings. The firing is controlled by a PIC chip, the firing cycle is depending on the different resistance load and power output desired...total of 10 sets of resistance load/power settings (I'll provide this later). There shouldn't be a need to load different programs for each load/model settings, I prefer one program which I then can cycle the different settings from off (meaning direct power to the unit, no duty cycle modulation) to 1,2, 3, etc to 10.
2) There should be a safety program that monitor voltage drop or other indicators which co-relate with no load (circuit open=no resistance). Upon no load, power output from the circuit should be cut. This safety program should always be the first thing running upon switching on of the unit. In the event of a fault (no load), after it cuts power output, it should repeatedly run the safety program...so called self reset & self diagnostic.
3) On top of this I would like to have a thermostat/temperature controller in the same circuit which will monitor surface temperature. At a programmable high temperature limit, it should switch off the power, it should then switch it back on 10 degrees below this. There should be 3 settings to this high temperature limits which can be selected by using a rotary dial (high = 65 deg c, medium = 50 deg c, low = 35 deg c), these setting should be programmable and not necessary to be very accurate (only the top limit of 65 deg C is critical, the lower settings are approximates). The temperature sensor should be as discreet as possible (meaning small).
4) The should be a maximum limit switch (basically a thermal fuse) which will cut off power to the unit at 105 deg C.
5) No display is necessary, except just one LED indicating power.
6) The unit should be as square as possible and as small as possible.