Wednesday, February 12, 2014

In other news...

This post doesn't really fit on the blog, but I don't have a better place to post it and some other DIYer out there may want to do something similar.

My wife inherited a nice Evenheat glass fusing kiln.  The only problem was that the 20-year-old temperature controller wasn't working.  After finding the manual for it online, she decided that she wanted something more flexible and user-friendly anyway.  I convinced her that it would be relatively simple and inexpensive to build a better temperature controller from scratch.  A replacement controller was available from the manufacturer and other compatible controllers are likely available, but it seemed like a good excuse to play with an Arduino board. 

After more time than I'm willing to admit, it's up and running!  Behold the Meltinator 9000:

And here's the obligatory cheeky initialization screen:

The kiln controller uses:
-an Arduino Uno board
-an Adafruit Arduino display shield
-an Adafruit protoshield
-a K-type thermocouple reader board (MAX31855 based)
-a resistor, BJT, and diode to drive the relays

Schematics would be overkill for this one.  The circuit to drive the relay was like the version linked below, but with the resistor value adjusted for the resistance of my relay coils.

Luckily, the new kiln controller fits nicely in the old enclosure.  That made life a lot easier.  Flipping through 19 bazillion pages of a Mouser catalogue to find the right enclosure and switch caps is no fun.

The software allows for 25 different fusing schedules to be programmed.  Each schedule has 10 steps.  Each step has a target temperature, a temperature rate of change, and a hold time.  The user can add time to the hold cycle of the current step during execution of a schedule, if needed. 

The software for the kiln controller can be found at github here.  Use at your own risk.

I ran a two-step test program earlier today and kept an eye on it to make sure the house didn't burn down.  First, it ramped up to 1500 degrees Farenheit at a rate of 2550 degrees per hour.  Then it cooled down to 500 degrees at a rate of 1000 degrees per hour.  Heat-up worked just as planned.  Cool down was slower than anticipated; the kiln is better insulated than I had thought.  I may need to prop the kiln lid open slightly during cooling if I want the controller to be able to control cool down accurately. 

To wrap things up, here's a picture of some of the stuff that Sarah makes in the kilns.  She's gotten really good!