This is reflow soldering controller for use with a toaster oven as reflow soldering oven.
I bought the toaster oven in a local super market for about 40 €. There was also a cheaper oven on sale, but I wasn’t sure if it did 250°C, so I bought the more expensive and prettier one.
Since I don’t want to loose the warranty and also haven’t any interest of the oven’s internals, I designed the reflow controller as an oven-external device which directly switches the oven’s mains on/off.
The relay I use is for 6V, but it seems to work just fine with the 5V supply from the ATtiny. On the mains side, the relay is rated for 230V/16A.
The whole controller is based on a ATtiny 45 µController. I use one pin as input for the 100k thermistor for temperature measurement (connected to JP3), one pin controls the mains relay (via a BC140 transistor), one pin controls a LED for feedback and one pin is connected to a switch for user input.
Disclaimer: If you plan to build such a thing, be aware that 220V (or 110V) are involved in this circuit. That voltage potentially kills you. So be careful and don’t do it if you’re not sure, what you’re doing!
Firmware
I managed to pack full PID controlled temperature management, 3 “programs” and a minimalistic UI into the 4k program memory of the ATtiny 45.
The main program (1) handles the reflow soldering process. It controls the oven’s temperature with the following temperature profile:
- heat up to 150°C
- hold this temperature for 40 seconds
- heat up to 190°C
- hold this temperature for 10 seconds
- heat up for 245°C
- hold this temperature for 10 seconds
- cool down
Read More: Reflow Soldering Controller