Cool Xmas Day project uses Papilio FPGA control

From HackADay:

"For Christmas, [Hamster]‘s wife gave him a mini-oven. Later that day, he tore it apart and built this FPGA controlled reflow oven.

We’ve seen plenty of reflow oven builds in the past. Most of those projects use a microcontroller to do closed loop control, sensing the temperature and toggling the heating element to hit a set point. This build uses the Papilio One FPGA development board as a controller. It implements a state machine that meets the reflow profile of the solder paste, ensuring SMD components are soldered properly.

The oven uses a MAX31855 to read temperature from a thermocouple. This device provides amplification, cold junction compensation, and analog to digital conversion which spits out the temperature over SPI. To control the heater, a 40A solid state relay is used.

The VHDL code that drives this oven is linked in the writeup, and has some interesting bits for those looking to experiment with FPGAs. It includes an SPI interface, display driver, and the temperature state machine logic."

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Comment by Overwatch on December 29, 2013 at 10:44am

What's the reason for using an FPGA here instead of a libc-compatible 8-bit microcontroller such as AVR? Other than "that's all I had lying around". More expensive, more difficult to program and debug...

Comment by Gary McCray on December 29, 2013 at 10:58am

This is an interesting exercise if what you want to do is learn about FPGAs and have a spare FPGA board lying around.

But if you just want to build a simple reflow oven almost any cheap micro dev board will work fine.

You need a micro board with a little IO, the above mentioned MAX31855, a K type thermocouple and a solid state relay sufficient to drive the toaster oven.

For a program you don't even need to use PIDs, just tell the relay to turn on if it is below the set point and off if it is above it, SSRs don't mind turning on and off a lot.

All the program needs to do is let you set ramp times, start and stop times and continuously recalculate the current desired temperature.

Made and Sold Kiln Controllers that worked this way for many years and they maintain very tight temperature control over the entire range of a K thermocouple.

I can't honestly see why the $130.00 FPGA board used here actually provides any advantage over the cheapest possible Arduino board. (I used PICs myself).

Comment by John Arne Birkeland on December 29, 2013 at 11:20am

DIY don't need no stinking reasons!.. :)

I have respect for these kind of projects, showing true hardcore DIY spirit.

Comment by John Githens on December 29, 2013 at 1:15pm

Mr. Birkeland's comment made me chuckle. For those who would like a historical reference, click here.

Comment by Shannon Morrisey on December 29, 2013 at 1:25pm

CORRECT!!! DIY needs not reason, only imagination.

I prefer FPGAs for 'simple' projects because they scale complexity up more easily.

mcu oven here from Spectrum

also, for those interested, cf. FPGA & MCU embedded applications:

Comment by Gary McCray on December 29, 2013 at 1:54pm

Hi Shannon, that conversion from Spectrum is really nice, the ramp soak PID controllers for only $85.00 from the company linked (Lightobject) are a great deal and they have the other stuff you might need as well.

Basically a no brainer at all.

Comment by Jack Crossfire on December 30, 2013 at 3:50am

That would make the next milestone a reflow oven controlled by discrete transistor logic.


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