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18 August 2011
Author: Giorgos Lazaridis
K-Type Thermocouple PID Controller

Worklog - Hacking the heater (September 4 2011)

I kept this dryer many months for such an occasion. It was a present that my girlfriend found in a shampoo package. She asked me if i wanted to keep this, and instead of a hair dryer i actually saw motor and a heater :D.

This is the hair dryer And this is an exploded view The heater resistor is 800 watts!

The motor is a 12V DC, it has 4 diodes to rectify the AC I will remove the wire and the switch from the heater resistor And i will keep the fan blades. The motor sounds like a train

The heater comes with a built-in mechanical bimetallic thermostat because we don't want the lady to have a thermal shock. I measured the temperature before i hack it, and it was 80 to 90oC. When i removed the thermostat the temperature climbed up to 300oC before i unplug it.

The heater comes with a built-in bimetallic thermostat I bridged the thermostat with a thick wire I added 2 new wires to power the heater
I will use the plastic cover cone to drive the air through the heater This is the final assembly of the heater. The base diameter fits perfectly on this PC fan

A faster thermocouple (September 10 2011)

I tried the thermocouple that i got from ebay to see how it reacts in temperature changes. This thermocouple has a large mass to heat, so the reaction is not very fast. So i decided to change the thermocouple with a smaller mass to have faster reaction to temperature changes:

This is the thermocouple with the large mass and slow reaction And this is a typical fast-acting K-type thermocouple for multimeters I don't need the socket for the multimeter This is what i'm going to use

The thermocouple is ready to work with the controller, and the controller is ready to be programmed!

The new (and hopefully final) schematic (September 13 2011)

So, if you have already read the previous pages and more specifically page #3, you may have notice that i made a few mistakes on the PCB which i had to fix them with two wire bridges. I tested the board with these wires and it seems that it works perfectly. So, here is the new (and hopefully last) schematic diagram of the PID controller:

Yet again, due to the fact that the image above is low resolution and the schematic is not very clear, i upload the eagle files for this project:

 K-Type Thermocouple PID Controller - Eagle Schematic V1.1

Explosion is something that can happen while prototyping (September 16 2011)

This is what happened: A little tiny bug in the software caused the output to go high rapidly. I was testing the controller while i was playing my favorite game. The incident first excited my nose. The heater became very hot, about 350oC, and the plastic cover took fire. But that's only the beginning. I tried to pull the thermocouple back and put off the fire, but the plastic had already melt and the thermocouple stuck in there. So i pulled it with force, but unfortunately the thermocouple wire touched the 220V resistor...

This is what happens when 220V goes through the MAX6675 The plastic went on fire And the thermocouple got a nice plastic coating ;)

So there will be a small delay to repair the controller...



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  • At 13 July 2014, 16:14:59 user Mike wrote:   [reply @ Mike]
    • Nice project and good presentation - are the programming codes available?


  • At 11 May 2014, 13:51:18 user panayiotis wrote:   [reply @ panayiotis]
    • file gia.molis tora se brika ke ise poli endiaferon. exo mia idea gia pio statheri thermokrasia gia pid temp controllers.nomizo pos tha itan kalitera an anti na kobete to power apo to heating elemend , apla na mionete kai na afksanete otan pesi I thermokrasia,etsi o xronos pou xriazete gia na ftafi I antistasi sto maximum pig temp tha ine poli ligoteri kai to lathos ligotero. ti nomizis, ? se efxaristo.

  • At 3 June 2013, 8:03:06 user Giorgos Lazaridis wrote:   [reply @ Giorgos Lazaridis]
    • @Angeltech Follow the schematic as shown - I added the wire after i discovered the problem with the PCB, so there may be pictures without the wire. I really cannot remember what happened.
      As for the fan, you need an oscilloscope to see if the PWM pulses arrive at the fan.

  • At 2 June 2013, 11:01:44 user Angeltech wrote:   [reply @ Angeltech]
    • Sir I have no luck with fan speed in 3 or 4pin fan still not working right, hope you could help another thing is do I have to connect pin 23 and pin 6 of microcontroller seems you just connect it and remove on the demonstration picture. please advice.

      Thank you very much.



  • At 2 June 2013, 10:29:57 user angeltech wrote:   [reply @ angeltech]
    • Sir thank you very much, now the 7 segment brightness is the same, still working on the fan problem maybe I have to change the darlington transistor which i used C4169 that contains diode and zener that might effect the control signal.

  • At 21 May 2013, 4:56:18 user Giorgos Lazaridis wrote:   [reply @ Giorgos Lazaridis]
    • @Angeltech I used 2 different display sets so i have different delays to have same brightness. What you want to do not is go to the "Display.inc" file and replace the "call Wait390uSec" with "call wait2mSec" (found 3 times).

      For the PWM, i'm not sure what the problem is. It should work.

  • At 18 May 2013, 16:11:24 user Angeltech wrote:   [reply @ Angeltech]
    • Hello Sir:

      I have duplicate your circuit and working with v.1.1 hex file program to the PIC chip, the problem I encountered is the following:

      1. 7-sigment display on the top portion all 3 7-segment displays is dim but it displays the temperature right. Not like the lower 3 7-segment is bright and clear with same 7 segment part number.

      2. the Fan controller pot not working, it never slows down as adjusted.

      Hope you could help me with this, I don't have very much background with regards to programming. and I really like the circuit and the functionality.



  • At 6 November 2012, 11:51:13 user Giorgos Lazaridis wrote:   [reply @ Giorgos Lazaridis]
    • @Iuliu well, actually i do, but i have not finish the housing. I stuck in the nozzle which was originally from special plastic, but it was eventually not so special to withstand the heat of the resistor which accidentally came into contact - so it burned into flames. I will make it from stainless steel or something like that.

  • At 3 November 2012, 18:56:27 user Iuliu wrote:   [reply @ Iuliu]
    • Hello Giorgos Lazaridis have you made the new proiect "a PCB preheater" ?
      I'm thinking to do my self to,but i want to use 16f819 ,that pic i have about 5 pieces,my question is is fast enough at 4 Mhz clock?

  • At 10 July 2012, 20:45:27 user Mr-H wrote:   [reply @ Mr-H]
    • Hi nice job
      but from what i see here, the systeme is unstable

  • At 25 June 2012, 5:03:46 user Giorgos Lazaridis wrote:   [reply @ Giorgos Lazaridis]
    • @Ricardo The layout had errors, check this page:
      I have not correct these errors, so you will need to find and correct them yourself. If this is ok with you, i can send the layout to your email. And if you correct these errors and it works, you can send them back so i can then upload them in the site.

  • At 24 June 2012, 20:57:24 user Ricardo wrote:   [reply @ Ricardo]
    • Hi! Could u provide us the layout of PCB?

  • At 24 June 2012, 15:48:30 user Giorgos Lazaridis wrote:   [reply @ Giorgos Lazaridis]
    • @Ricardo unfortunately i cannot help you with this. you need to do it yourself.

  • At 24 June 2012, 15:32:47 user Ricardo wrote:   [reply @ Ricardo]
    • Ok, I just want to know how to do the change of 16F1937 to another one like 16F877A or 18F4520. Can u help us with this? Regards!

  • At 24 June 2012, 11:48:35 user Giorgos Lazaridis wrote:   [reply @ Giorgos Lazaridis]
    • @Ricardo The worklog is here:

      There are 5 pages in which i explain exactly how i made it. As for the parts, i cannot help you with them. You need to locate them from your local market, or order them from internet like from farnell.com

  • At 24 June 2012, 10:59:40 user Ricardo wrote:   [reply @ Ricardo]
    • Hi! I know there are a lot of information in your website but I can not find some parts like these:
      IC1 PIC 16F1937 Microcontroller
      IC3 MAX 6675 Cold-junction compensated K-Thermocouple to digital converter (0°C to 1024°C)
      IC5 ULN2003A High Voltage - High Current Darlington Arrays
      IC6 MOC3021 Random Phase Optoisolator TRIAC Driver Output
      IC7 DF02M 1.5 Ampere Bridge Rectifiers
      Also, I'd like to ask you the source code in assembly...

  • At 23 June 2012, 16:29:45 user Giorgos Lazaridis wrote:   [reply @ Giorgos Lazaridis]
    • @Ricardo But everything is in my site. go to the worklog tab and you will find everything there.

  • At 23 June 2012, 16:17:14 user Ricardo wrote:   [reply @ Ricardo]
    • Hi! Assembly it will be nice for me...Can you provide the source code? I want to buy the hardware (PCB) already done/working but I need the 18F4520 instead 16Fxxxx. I don't have time to do it myself and I won't find some parts in my place so, let's talk about...Can you help me? Since now, thanks a lot!

  • At 23 June 2012, 6:08:32 user Giorgos Lazaridis wrote:   [reply @ Giorgos Lazaridis]
    • @Ricardo hello! I'm sorry but i do not program in C, only in assembly.

  • At 23 June 2012, 1:47:32 user Ricardo wrote:   [reply @ Ricardo]
    • Hello!! How's it going? I'm stating Control&Automation Engineering and I liked your job..very nice! So, I have a question, Is there any chance you provide me the source code in C ? I would like to learn how to program PID ALg into a PIC18F4550 using MikroC compiler so, could u help me, please? In last case, Do u have PayPal account? ;) Let's go deal!

  • At 27 January 2012, 12:26:09 user Giorgos Lazaridis wrote:   [reply @ Giorgos Lazaridis]
    • @awan i've been trying to convert the old-style articles (like this one) with the new style articles. I have already upload the TCPDF library, but i cannot get it to work. I hope everything will work well in the end.

  • At 27 January 2012, 6:39:54 user awan wrote:   [reply @ awan]
    • thanks bro for sharing ur project it will be very kind if u share pcb file for this project ....

  • At 8 November 2011, 2:17:21 user Brian S wrote:   [reply @ Brian S]
    • Thanks for the details. It is a pleasure to read or listen to your instructive discussions regarding your interesting projects. I like your attention to intelligent detail.

  • At 22 August 2011, 11:59:14 user Kammenos wrote:   [reply @ Kammenos]
    • @Drone i have both of them in stock ;) I think that MAX6675 is discontinued

  • At 22 August 2011, 11:51:32 user Drone wrote:   [reply @ Drone]
    • Don't use the MAX6675. In late June this year Maxim came out with the MAX31855. It is a better part IMO.

  • At 22 August 2011, 11:25:35 user Kammenos wrote:   [reply @ Kammenos]
    • @Fung they are different brands. Same type, same connection, different brand.

  • At 21 August 2011, 16:03:25 user Fung wrote:   [reply @ Fung]
    • Why do 3 of the 7-segment displays have different surface color? Are they specified to use?

  • At 18 August 2011, 22:35:09 user _pike wrote:   [reply @ _pike]
    • My opinion is to buy the same chip instead of trying to recompile the full programm also sometimes some fuctions are different from pic to pic....it is not worthy recompiling....

  • At 18 August 2011, 17:06:43 user Kammenos wrote:   [reply @ Kammenos]
    • @Stefan i'm sorry but i do not do circuits (nor programs) on demand. You will need to do the change yourself, or get a same PIC. As for the ULN, it is a darlington pair array. Instead of using 6 transistors i use this.

  • At 18 August 2011, 16:42:49 user Stefan wrote:   [reply @ Stefan]
    • Good job,I have a plans for this,but there not in function.So I would like you to finish this project and to build one for myself.But I don't have that PIC microcontroller that you're using I want to use PIC16F877A(887 etc.) can you recompile for it?And I want to know why there is ULN2023,what is his job? :D

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