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Home Made Kiln Controller


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#1 High Bridge Pottery

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Posted 04 August 2015 - 11:36 AM

I have always been interested in electronics, still remember designing and making PCB back in school. The availability of good reasonably priced electronics is amazing, also a lot of rubbish out there too :D

 

Did a bit of research into the Raspberry Pi last night and thermocouple measuring. Came across this product that is designed for a type K thermocouple, not the best for cone 10, but, after searching the forum if I can desolder the type K chip and purchase the right thermocouple type it 'should' work.

 

Is it best to go for type S, or type N or type R. I am a little lost there. New chip seems to be around $5

 

No idea how this is going to work out, only studied basic programming on linux but there seem to be enough tutorials out there to copy and past my way to something that could work.

 

http://www.adafruit.com/products/269

 

The MAX31855 performs cold-junction compensation and digitizes the signal from a K-, J-, N-, T-, S-, R-, or E-type thermocouple. The data is output in a signed 14-bit, SPI-compatible, read-only format. This converter resolves temperatures to 0.25°C, allows readings as high as +1800°C and as low as -270°C, and exhibits thermocouple accuracy of ±2°C for temperatures ranging from -200°C to +700°C for K-type thermocouples. For full range accuracies and other thermocouple types, see the Thermal Characteristics specifications in the full data sheet.


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#2 Joseph F

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Posted 04 August 2015 - 12:20 PM

From their site:

 

https://learn.adafru...an-electric-imp

 

the only issue i can see is that they say the K type thermocouple is the only one that will work with your chip. 

  • Will not work with any other kind of thermocouple other than K type

 

It looks like that K Type will only go to 900F before it melts. So that definitely wont work for cone 10. 

 

Their site is hard to understand, but from the wording it seems: the Max6675 the upgraded chip is no longer made. So I don't know what that means for your high heats. 

 

It would be cool to program this. I do a lot of small programming on the side for simple things that I need, but no idea how to even start with a rasberry pi. I assume it uses python, which is a pretty well documented language that I have used a fair bit for scripted tasks.



#3 High Bridge Pottery

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Posted 04 August 2015 - 12:40 PM

Adafruit only sell the type K thermocouple as that is what people want. If you search for the chip number MAX31855 you can find all the type chips. The only thread I could find on the forum about this is here https://forums.adafr...=type s#p395238 but they seem to say it will work fine.

 

Ordered a Pi and the board, you can also seem to get free sample chips from the manufacturer so ordered type s chips. Going to be a steep learning curve.


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#4 Joseph F

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Posted 04 August 2015 - 12:43 PM

cool.



#5 High Bridge Pottery

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Posted 04 August 2015 - 06:18 PM

Seems to use python, or at least it can and that is what people choose to program in. Been reading a few tutorials on using the General Purpose Input Output GPIO pins and they are all using python. The adafruit tutorial seems easy enough that I can achieve it. Has a simple python script that prints out the temperature every second or so. Using that info instead to control a relay is going to be the hard part. 


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#6 Joseph F

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Posted 04 August 2015 - 08:13 PM

Are you going to build a mechanical controller for your burner to vary based off the rasp pi readouts?



#7 High Bridge Pottery

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Posted 04 August 2015 - 08:18 PM

Nothing like that right now. I have a small 13A electric kiln that needs some temperature control. I ripped out the old electrics as they didn't work. Before that I will probably set up something to log my firings in the kiln that I know works, has a controller and has a reliable profile to compare the homemade thermocouple results to.

 

Been looking into switching relays with the Pi tonight, seems you can get some solid state relays that switch with as low as 3v. Going to look into how you up a 3.3v to the 12v relays I have now.


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#8 Joseph F

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Posted 04 August 2015 - 08:23 PM

Ah, I missed the relay part. I imagine controlling relays isn't to difficult if you can pull in temps. You could set up an easy loop to constantly check temps and adjust the relay based on rules you setup. That part would be easy. I imagine figuring out how much you need to click on and off to raise temps and control temps is going to be the hard part. Considering that as the heat needed increases you will have to have different algorithms. 



#9 Joseph F

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Posted 04 August 2015 - 08:24 PM

Thinking about it, you could teach your program how good your kiln heats and cools pretty quickly by building some test then recording that data then reprogramming, and repeating the test. It would take a while and you would have to continue fine tuning along the way, but I imagine you could probably get some firings going within a week or two of testing heating rates.



#10 High Bridge Pottery

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Posted 04 August 2015 - 08:34 PM

Yes, how much 'on' for how much temperature increase will be interesting to work out. If I can get something that can log my temperature and send it to the internet so I can see the temp and if my kiln is finished firing I will be happy. That sounds like the place to start anyway, using it as a mod on my existing kiln.


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#11 Joseph F

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Posted 04 August 2015 - 08:38 PM

The sending the temp to the internet problem is not hard at all. That will be the easiest part programming wise imo. 

 

You are making me want to get back into programming again. It has been a while since I had to think about logic behind an idea.



#12 Joseph F

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Posted 04 August 2015 - 08:40 PM

BTW I will be happy to help you with any logic overview concepts. I don't know how to program a pi, never even held one, read and seen a lot of really awesome things on hacker news about them. But they came out when I was sorta phasing out of my development career. Got tired of dealing with people who didn't understand want they wanted. 

 

But I can help with logical processes and the big picture of how you should do things and maybe even some python scripts if you have some problems. 



#13 High Bridge Pottery

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Posted 04 August 2015 - 09:08 PM

Thank you :D sure I will have some badly written code for you to look over in the future. 

 

Going to have a lot of hardware issues before that and general electronic design to learn. First stop is a blinking LED. hopefully it will have been delivered tomorrow so I can pick it up and start messing around. The kit really isn't that expensive and is seems lots of companies are now making boards that can do anything with these new microprocessors or computers really, whatever brand you go for.


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#14 Pieter Mostert

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Posted 05 August 2015 - 05:48 AM

High Bridge, I spent quite a bit of time researching DIY controllers earlier this year after my kiln's controller died. For a while I was heading towards using an Arduino Uno with the MAX31855K chip, but I ended up just getting a PID ramp/soak controller from Auber Instruments. I don't have your electronics background, so I didn't want to have deal with trouble-shooting any issues that might occur, and the Auber controller wasn't that much more expensive. But programming a controller would have been fun.

 

If you want to program a PID controller, this is an excellent webpage:
http://brettbeaurega...d-introduction/
You'll have to translate the code to use with a Raspberry Pi though.

The guy who wrote the code, Brett Beauregard, is also involved in the production of an open source PID controller. When I was doing my research they were having some technical trouble, but they seem to be up and running again.

 

Lastly, I thought I'd throw this out for anyone else interested:

http://www.jameco.co...-resonator.html

It's cheap, but too advanced for my skills and I couldn't find any reviews of how well it works.

Let us know how your controller turns out. I'm pretty happy with my Auber controller, but if I get a kiln that needs zone control one day, I'd like to try making my own.
 



#15 High Bridge Pottery

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Posted 05 August 2015 - 09:40 AM

Thank you for the information :D will be great to have a look through the code and how they are getting it to read temperature.

 

I wouldn't say I have an electronics background  :unsure: it was 2 years of basic education 10 years ago :D It's just kiln controllers are the last mystery in understanding how to work a kiln and I want to know!


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#16 jrgpots

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Posted 05 August 2015 - 09:27 PM

Will you use one of the KISS software programs available?

Jed

#17 Joseph F

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Posted 06 August 2015 - 01:09 PM

High Bridge Kiln Company, ready yet?  ^_^



#18 High Bridge Pottery

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Posted 07 August 2015 - 12:51 PM

Does that mean Keep it simple stupid? If so I am going to keep it very stupid :D

 

Will you use one of the KISS software programs available?

Jed

 

Heyy, you never know. If I can work out something it could be a big seller  ;) Pi arrived yesterday, thought it was broken for an hour before I swapped out the HDMI it arrived with... So much for cheap HDMI cables, brand new and doesn't even work.

 

Had a little play around with some tutorials, having a lot of fun. I now have an LED that comes on when I get a new email, loool.

I think the breakout thermocouple chip arrived but I haven't been to the studio again to pick it up.

High Bridge Kiln Company, ready yet?  ^_^


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#19 Bob Coyle

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Posted 07 August 2015 - 06:22 PM

http://forum.arduino...?topic=208061.0

 

The above is a link to the Arduino MAX31855 library . Why re-invent the wheel. I have been using the Arduino to control my kiln for several years.

 

Here is the code I use.

 

#include <MAX31855.h>

float tempOut = 0;
int command = 0;
int value;
// Adruino 1.0 pre-defines these variables
//int SCk = 13;
//int MISO = 12;//SO
//int SS = 11;//CS

// Setup the variables we are going to use.
double tempTC, tempCJC;
bool faultOpen, faultShortGND, faultShortVCC, x;
bool temp_unit = 0; // 0 = Celsius, 1 = Fahrenheit
//temp(SCk,CS,SO)
MAX31855 temp(11, 12, 13);

void setup() {
 
  pinMode(2, OUTPUT);      // Test Com Reset issue  
  pinMode(3, OUTPUT);
  pinMode(9, OUTPUT);
  pinMode (10,OUTPUT);
  digitalWrite(10, HIGH);

  Serial.begin(9600);

}

void Average10() { // average 10 readings
 
  float Ave;
  int AveCt ;
  AveCt =0;
  Ave = 0;
  delay(50);
  do {
 
      temp.readMAX31855(&tempTC, &tempCJC, &faultOpen, &faultShortGND, &faultShortVCC, temp_unit);
      Ave = Ave +  tempTC ; // tempTC ;
      AveCt = AveCt + 1;
      delay(10);
     } while  (AveCt < 10 ) ;
 
    tempOut = (Ave/10);
 }

void loop() {
   if ( analogRead(0)> 1021) {          // it's too high turn it off
          digitalWrite(2,LOW);
      }
     value = 0;
     Serial.flush();
     if (Serial.available()) {      // Look for char in serial que and process if found
      command = Serial.read();
      if (command == 84 ) { // If command = "T" turn it on (unless to high)
          digitalWrite(2,HIGH);
         // delay (500); // keep it on for at least half a sec to prevent bounce
      }
      if (command == 67) {          // If command = "C" turn it off
          digitalWrite(2,LOW);
         // delay(500); // keep it off for at least half a second to prevent bounce
      }
      if (command==68){                 //if command ="D" sound tone
        tone(9,220);
      }
      if (command==69){                 //if command ="E" end tone
        noTone(9);
      }
          command = 0;                 // reset command
   }
    delay(50);
    Average10(); // take averaged sample
    delay(50);
    Serial.flush();
 
    Serial.print("@- ");
    Serial.print(tempOut);       // output to computer USB port
    Serial.println(" -Tmp ");
 
 }

 

I use a Visual basic or a Java software  interface to do the logic to control the kiln. You can use any code that allows you to read/write from a usb device. 

A solid state relay is used to toggle the kiln on and off directly from the Arduino.

 

I use an AD595 chip rather then the MAX because Of noise problems. The AD595 is a very stable A/D for type K thermocouples. It works pretty much the same except you have to run it through a op amp.

 

Do some research on Google... there is a lot out there already done for you.

 

.



#20 High Bridge Pottery

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Posted 07 August 2015 - 07:17 PM

Sorry :D you are going to have to take this through slowly. So the library lets you call predefined code?things?statements? that work with the hardware? I have used libraries but never really understood them.

 

You then have your program that has these scripts?things?statements? that you use in some java software? All I could work out from the code is defining the variables, a strange serial bit and telling it how to turn on and off.

 

Going to have to have a good look at your code, thank you for sharing. I'm not trying to invent the wheel and I 'dodo' a lot of googling, the problem I think is how little I know to start with :D No reinvention just ignorance 


One physical test is worth a thousand expert opinions.

 

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