Raspberry Pi Solder Reflow Oven Controller - Part 2

Posting project on behalf of user diamondjimkoehler:

Continued from Part 1

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For diagnostic purposes, the oven program creates graph, named “temp.png”, after it has completed the reflow process. This graph shows the input temperature profile it was following as well as the actual temperature vs time that occurred. An example graph, so produced, is shown below. Here, the desired temperature profile was just to go to 210 C and stay there. When there, the controller flashed the "Ready" LED and turned the oven off; I immediately opened the oven door when the “Ready” LED came on. As you can see, the oven temperature was greater than 188 C for more than 20 seconds but, I might have waited a bit longer before opening the door. With the door closed, the temperature drops much more slowly and the additional time with a temperature near 210 C might have been a better choice.

Nevertheless, the results were quite good. For that reflow cycle, I had taken a old pc-board from a previous project, applied solder paste as I’d described in the ARRL article on a few pads and put on some random components. At the left, there is an image of that section of that pc-board after the cycle. These are 0805 size SMD components and, as you can see, the solder paste reflowed very well … the solder pads are bright and clean.

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The object of the exercise has been completed. I have a prototype of a working reflow solder oven. The controller is simple; to make a reflow soldered board, it is just a matter of preparing the pc-board by putting on the solder paste and components, putting it in the oven and pressing a button. The program does the rest. All that is necessary is to open the oven door a few seconds after the “READY” LED starts flashing.

It is my intention, for the next phase of the contest, to re-design the circuit to fit on a Raspberry Pi ‘hat’; a small pc-board which can be plugged onto the Raspberry Pi Zero W header. There is enough room for almost all the circuit. Only the solid-state relay will need to remain on the chassis. The final controller can be physically quite a bit smaller than my prototype. I think adding a piezo-electric buzzer to create a ‘beep’ when the reflow process is over would be a good addition. The overall cost of replicating the controller would be probably be between about $25 and $50.

The firmware should be refined a little.

Finally, I propose to submit a construction article to the ARRL as a follow-up to the article I wrote in 2011. It would offer a very inexpensive alternative to commercial units and would be simple to replicate.

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