Reflow Soldering Controller

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.
Reflow Soldering Controller
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!


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:

  1. heat up to 150°C
  2. hold this temperature for 40 seconds
  3. heat up to 190°C
  4. hold this temperature for 10 seconds
  5. heat up for 245°C
  6. hold this temperature for 10 seconds
  7. cool down

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