Oven controller (arduino based)

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pardydon:
re the comment about the max 31855 . I used the chip on a board from adafruit . about $18. Nice bit of work from them , very easy to use. Returns a temp compensated reading.
Thanks to rschilp for the code....very similar to my approach. I will learn from your code as you are much better at it than I am . I have a background in electronics but the coding is new to me. I find it just amazing what is possible with open source and sites like this one....

Dawai:
This project kinda makes me want to build another Electromelt clone. That was the handiest small casting device I've had yet. (looks like the code would work as easily in there as a aluminum smelter, firewood boiler or...)

With enough ingenuity, people are doing anything & everything with the arduino's.

rschilp:
I used the max 31855 from adafruit as well, although it is pricey, it is a very nice piece of equipment that makes working with the thermocouple so much easier.

It would be VERY easy to use the code as is or modify it make it useable for all kinds of temperature control situations. If you do modify the code, please share it in the public domain and post a link here where we can find the updated code so we can all benefit and learn.

The code has a nice way to set the maximum allowed variation (variable is called variation) and is currently set to 2% of target temp (target/50) that is a parameter you may want to play with for any process that has a larger or smaller tolerance. The current setup (code) will allow a process that maintains 1000C to get down to as low as 980C before turning on the heat again.

Looking at the code it really needs a function to do timed ramp up and ramp down, allowing for slower warming and/or cooling then is the case with the heater on or off at 100% duty cycle. If I find some time in the next few weeks I may add that code, if I do I'll post the updated source here.

On the hardware side I don't control the power to the oven heating element directly, although the solid state relays I used is large enough to handle the load, I decided to open up my kiln and use the build in safety circuit (still 220v but draws much less amperage than the heater circuit) as the switching circuit, safer and cleaner solution in my opinion.

The kiln has two air vent holes, my future plan calls for the installation of some actuators on those for open/close functionality and a small computer type fan (very low cfm/pressure) on one to allow me to control evaporation and help cool the over faster than just turning the power off, and with the help of the fan (on/off/speed) control the rate of cooling.

Dawai:
http://www.ebay.com/itm/1pc-KYOTTO-AC-Solid-State-Relay-SSR-KR2075AX-280VAC-75A-Variable-Resistor-IN-/130662445830?pt=LH_DefaultDomain_0&hash=item1e6c16b306

What I think you are asking? Proportional output HOW TO?? simply.. the SSRV listed there on ebay is a variable output solid state relay that takes a variable resistor pot to "turn on and adjust the level" of the output, up to 75 amps.

Last time I did this, I used a switching device a MOC3010 opto-triac driver and parallel resistors in line with the outputs.. by selecting them binary value increments (each successive resistor half previous) you could select a proportional output. with all on = 100%, etc.. simply, nothing to really build.. It did use up a few outputs. I think I had 4 steps on that one.

I did this with a vfd inverter recently too, used the "programmable logic binary inputs" on the vfd terminal strip to vary speeds with a plc.. relay output, hard contacts.. the brick PLC had no analog or pwm frequency output.

Perhaps this can help with "electrical logic" for someone elses' project. Kinda a sideways approach, but a cheap one, us hillbillies like cheap.

pardydon:
Here is a very simple bit of code.

//output to element 25%
void heatLow(){
digitalWrite(ledPin,HIGH);
delay(2000);//on time 2 sec
digitalWrite(ledPin,LOW);
delay(6000);//off time 6 sec
}//end of function

Kiln elements need many seconds to heat up. I use a SSR for each of three elements. The original manual controls cycled on an eight second period so I just mimicked that.
Arduino can use timing or target temperature or ?? for whatever you want.

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