I managed to get the Thermocouple Amplifier (MAX6675) breakout board – v1.0 from Adafruit working without issue. I downloaded the library they had stashed at GitHub and everything went according to plan. I played a bit with the ‘bake’ and ‘toast’ settings of the oven. Bake only powers the bottom heating element while toast powers both. The heating slew rate needed to follow the reflow profile would only be supported by the toast setting so I went with that.
I had the end of the K-type thermocouple fastened to a piece of pcb material with kapton tape and placed that about is the x-y center of the oven. The oven was set to maximum (no regulating yet). The blue plot was just wire rack shelf closest to the bottom of the oven. The red plot was with the broiling pan on top of the wire rack. You can see the one with the pan was slower to rise and fall. The sudden change in the downslope is where the door was opened and the tray pulled out.
Thank you Coolterm!
At first I was unable capture data for plotting. It was frustrating when I went to go copy and paste it out of the terminal window. For some reason the Arduino IDE doesn’t do this. After cruizing the web for solutions I found a good one. I was able to record time and temperature by printing them out with the serial command and capturing the output with CoolTerm. Cool Term is a very nice terminal program that allows you to copy & caste captured serial data as well as capture it to a file.
Now that I had the data I wanted to plot it out so I could see how fast the temperature was changing. I tried Google and Open Office spreadsheet programs to do this. I don’t know what I was doing wrong but it was difficult to get the temperature on the X-Axis. All columns wanted to be on the Y axis and I couldn’t find an option to change this. Then I remembered that I had MathCad on an old laptop. I was able to import the data and make a graph comparing the 2 runs.
It looks like this toaster oven will work. For small boards, some sort of aluminum tray or plate will be needed to prevent the boards from falling through the wire rack. I don’t think the broiling pan will do as it has an uneven surface.
- Buy a solid state relay
- Write the Arduino code for the temperature profile
- Find a better plotting solution for looking at the temperature vs time.