Actually bought the parts months ago but didn't get around to building it till this month. The basic idea is to use any dumb oven with minimal modification and be as simple as possible.
Basic functions:
8 phases that can be up to 10 minutes long, adjustable in 10s increments. Each phase has a target temperature up to 360C in 20C increments. When the set time in each phase is reached the controller move on to the next phase until it rolls over to #0 which is the stop phase.The profile is auto saved to eeprom when ever it is changed.
The controller checks the MAX6675 thermocouple decoder at 4Hz rate, if it's lower temperature than the target it turns on the SSR. So it's a pretty basic controller, your average toaster oven doesn't really have that much power to warrant a full PID anyway.
Currently I have a AC zero crossing detection circuit nut haven't really made use of it yet. The SSR is already equipped with ZC function.
Display switches between:
-#- current phase #
### temperature in C, blinks the target temp if you press the "edit" button to edit the profile.
##.# count down to the next phase in seconds, blinks the phase duration if you press the "edit" button to edit the profile.
The second decimal point indicates the state of the SSR, so in the picture below the SSR is ON and temperature is at 199C.
While I have 5 buttons I really only need 4 (Menu/Edit/+/-)
A few thermal shots taken with the imager at work (Fluke Ti10, this thing is awesome!)
The bright spot is the resistor divider for the zero crossing. To show the temperature of the SSR while it's conducting around 5.5A I stuck a piece of silicone thermo pad on it, with the toaster oven I tried it with a heatsink is not really needed.
Major components:
RAC03-05SC AC/DC converter, massive overkill for the job, the only reason I picked it was because it was board mount. Considering that I am only loading it at maybe 40mA any one-hung-low 5v usb wall wart would have served just as well.
G3NE-220T-2-US DC5 Solid State Relay, rated for 20A so I got plenty of head room for bigger ovens.
LCD-S301C31TR 3 digit LCD, dirt cheap and easy to drive. I have character LCDs in my junk box but I wanted something simple.
MAX6675 thermocouple decoder, went EOL by the time I got around to using it, Maxim has released the MAX31855 which only cost half as much...
ATmega8535, I simply filtered for the cheapest AVR that had enough IOs on mouser.