Several weeks ago I set out to build my own DIY reflow oven so I can start working with surface mount sensors, which are often cheaper and smaller. This post is a progress report on the first part of the project.

Assembling Bill of Materials

I'm building the DIY reflow oven based on this instructable. In order to make the project more likely to complete in a reasonable amount of time I decided to rely on breakout boards and prebuilt circuits. I set out by first assembling a bill of materials to estimate the cost of this project. The bill of materials, which comes out to about $100, includes:

Testing the Thermocouple

Once I got my breakout board and thermocouple in the mail I put them together and ran the example Arduino code provided on AdaFruit. It turns out that, as people have noticed, the thermocouples have incorrectly colored wires. This was easily fixed by reversing the wires. I also removed the heat shrink tubing on the tip of the sensor with a knife. The heat shrink is rated only up to 250 Celsius, which I think I will exceed.

termocouple setup

Rewiring the Oven

To rewire the toaster oven I first had to take it apart. Not surprisingly, it was mostly empty inside. Since the modified oven will be functioning similarly to its original setup not much of the wiring needed modification.The hot wire was already connected to one end of both heating elements so I just connected the other end of the heating elements to terminal 1 of the SSR. I used a 2-male to 1-female connector from RadioShack to connect the heating elements to one terminal on the SSR. I connected Terminal 2 of the SSR to neutral to complete the circuit. I put 5V from my Arduino across terminals 3 and 4 to turn on the relay, creating a return path for current to pass through the heating elements. You can see that the toaster was successfully turned on.

toaster on

The wires inside the oven are temperature resistant, so I put away the extra wires for later reuse. Unlike many other DIY-ers I also plan to keep the knobs in place for aesthetics. Now, all I have to do is install the thermocouple, mount the electronic hardware, and digitally control the temperature using the Arduino.