Toast-R-Reflow

I went through the exercise of designing a new power board that includes a DC power supply. I'm not sure the result is worth doing, though.

I added the footprint for a CUI VSK-S3 AC/DC module and changed the 3 pin screw terminal for a 4 pin one, with the 4th pin being the DC supply out for the controller. The trouble is that the board is now more than twice as large as it was, and the CUI power supply adds around $25 to the retail price - all to save you the trouble of just using a wall wart to power the controller separately.

I've added the latest EAGLE design files for the two controller variants, the power board and a new SMD variant of the power board.

I'm still keeping the files around for a through-hole power board variant, as it solves the bootstrap problem. To build your very first reflow oven, you can use the through-hole power board, modify the oven, and then use an Arduino Uno and a thermocouple amplifier breakout board and jumpers as your first controller. Once you have that working, you can reflow an SMD controller and switch over to that.

To make an Arduino Uno based reflow controller, buy an Uno, an AdaFruit i2c 2x16 LCD shield and an AdaFruit MAX31855 breakout board. SparkFun has a similar breakout board, but the AdaFruit one has a 3.3v LDO and level shifters so that it's 5v tolerant.

Connect the breakout board ground to the Uno ground, Vin to 5V, !CS to D7, SCK to D13, DO to D12. Connect D2 and D3 to 150Ω resistors in series with the element lines for the oven. Connect a K thermocouple to the breakout board and route it somewhere convenient inside the oven.

With that done, grab the i2c display version of the sketch from the GitHub repository. You will need the Arduino PID library and the LiquidTWI2 library to control the display. Upload that code into the Uno.

The inventory of boards is getting low, so it's time to consider feature-adds for the next generation of Toast-R-Reflow.

The next version of the power board will be SMD. It's actually just a lot less effort for me to build the SMD portions of the board than to kit all of the through-hole parts. It will still be sold as a "quick kit" - the remaining through-hole parts (the triacs and their heat sinks, and the I/O block) will need to be assembled by the buyer.

One other thing I'm considering is adding an AC-DC power module so that the toaster could supply the DC needs of the controller.

I'm also considering changing the control method. With a DC supply on the board, I can change the control mechanism to be open-collector rather than the current 20 mA current mechanism (that is, lighting an LED).

The AC-DC supply would, however, likely add $10 to the price of the power board, and perhaps knock a couple bucks off the price of the controller(s), as well as eliminating the need for a separate wall wart.

I'd like design feedback. If anyone has any suggestions,

If anyone reading this has a Toast-R-Reflow controller, please go get the latest firmware from Github.

The change adds support for the AVR watchdog. The oven at The Hacker Dojo was discovered wedged somehow with one of the elements turned on. It's not immediately clear what happened, or if the watchdog would have prevented it, but the watchdog certainly can't prevent anything if it's not used.