About modified old oven to reflow oven for pcb. In this oven added temperature controller.
The whole thing is based around mega8 chip. There should be enough space for some pid, ramp generator, and menu. Oscillator is internal RC 8MHz.
User output is through 8x2 lcd display. Tiny display that will fit to the control panel nicely. This display is driven in 4-bit mode, to limit number of IOs. Backlight can also be controlled by the mcu.
User input is encoder with button. Both encoder pins are interrupt. Button is polled to save some nasty logic needed to multiplex.
Temperature is sensed by thermocouple and converted to digital using max6675, that i had lying around. Datasheet is saying that data is available every ~200ms. Little slow, but enough for this purpose. Big plus is cold junction temperature compensation and polynomial compensation.
Output is 2 channel PWM, 0-Vin. Both to be used to drive SSR (solid state relay). These relays can be bought off fleabay for about 3-6dollars/pc (free s/h).
Serial port is used to talk to bootloader, and to transmit temperature for further analysis (pid tuning)
Powered by 5.70-12V, voltage is regulated by micrel mic5202-5.0 (same as on BP)
There is no programming port for the atmega8. It needs to be programmed with bootloader before the max6675 is soldered. Reset and MISO pads are for this purpose.
