MSP430 Reflow Oven Controller

I’ve been tinkering with some other projects which require the use of QFN and BGA parts which means that no matter how good I think I am at soldering, I still need to have some means of reflowing circuit boards.

There are many other projects around which document how to use an Arduino and a $30 toaster oven from WalMart to build a reflow oven, but I wanted to do something a bit differently. I’ve put together some hardware to use an MSP430 Launchpad and a solid state relay to build a reflow oven. Kristen has also taken some of the code from rocketscream, optimized it, and ported it over to the MSP430. Some of the profiles have been tweaked, and timers are now run using interrupts instead of global delay() functions. The code can be found up on github here.

So, let’s get started! First things first. I purchased a Black & Decker Convection oven from WalMart. It seems to work well and is capable of reaching ~240 C, although it’s not very well insulated. More on that later.

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 I chose to keep all of the high voltage connections inside of the oven chassis since I don’t want to risk hurting anyone who uses the oven. I traced the “Hot” side of the AC line to the main thermostat and insert the SSR between the leads. This allows the software to pulse the heater elements on and off as needed in order to follow a proper reflow curve. I chose a solid state relay which had a rating greater than the maximum draw of a typical household outlet. I didn’t want to take any chances, and also the price difference was negligible. I used an Opto22 SSR rated at 120V AC, 20A. It was purchased off eBay for about ~$15USD. I repurposed some of the ventilation holes as mounting holes, and made sure that the relay was firmly attached.

2013-07-14 16.07.05Once that was finished, I worked on wiring up the power supply and thermostat amplifier to a socket. This was done in order to allow the MSP430 to be disconnected from the oven easily while transporting. I took an inexpensive 5V supply apart and connected it directly to the oven’s AC input. I wanted to not have to power the control board separately and make a single connection provide everything the oven needs to function.

DSC_6656_CommentedI used a MAX31855 breakout board sold by Adafruit as well as a Type K sensor wrapped in glass shielding to protect it from high temperatures. I chose to zip tie it to the back of the chassis and have not had any issues, but if you feel that you would like to change where this is located, go for it! I should also note that I used some Teflon-coated wire for this project in order to make sure that the wires didn’t burn. This may not be necessary, but it’s better to be safe than sorry!!

Once you’ve modified your oven, close it all up and move on to the control board!

The microprocessor chosen for this project is an MSP430G2553 installed in an MSP430 Launchpad. I wanted to keep the project lower-cost, which meant avoiding the Stellaris and Arduino platforms. The 2253 has two hardware timers and the ability to trigger interrupts using both timers and external I/O. Both of these features are required for this project.

This is what Rev. 1 of the board looks like. I’ve updated the schematic with some extra optimizations and features, but haven’t had it fabricated yet.

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The entire board sits over the Launchpad’s I/O ports and is not obstructed by any other hardware. The interface is very simple, there are only two buttons one controls the solder profile selection, and the other will start/stop the reflow program.

Screw terminals have been provided to allow for different cable configurations to be used. For my final version, I may consider adding an RJ45 connector instead.

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The two capacitors sticking out of the board are to reduce noise generated from an external power source I’m using. They are not present on Rev. 2, since there is an onboard regulator which completely bypasses the regulator on the Launchpad. Once you put the hardware together, connect the board to your PC, and upload the code, you should be ready to reflow!

Below are all the download links to the PCB files, schematics, and code. All material is shared under the Creative Commons Attribution Share-Alike 3.0 License. Please contact me if you are interested in manufacturing this design, or a variant.

MSP_Reflow_Oven_Rev2.zip

MSP430 Reflow Oven Code

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