# Termo relay on arduino i need help

**URL:** <https://forum.arduino.cc/t/termo-relay-on-arduino-i-need-help/1381244>\
**Category:** General Guidance\
**Created:** [May 13, 2025, 6:07pm UTC](https://forum.arduino.cc/t/termo-relay-on-arduino-i-need-help/1381244 "2025-05-13T18:07:43Z")\
**Posts on this page:** 20\
**Page:** 1

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**Author:** ![ardduino\_noob](https://dub1.discourse-cdn.com/arduino/user_avatar/forum.arduino.cc/ardduino_noob/32/1179114_2.png) [@ardduino\_noob](https://forum.arduino.cc/u/ardduino_noob)\
**Post date:** [May 13, 2025, 6:07pm UTC](https://forum.arduino.cc/t/termo-relay-on-arduino-i-need-help/1381244/1 "2025-05-13T18:07:43Z")

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![Зображення WhatsApp, дата_ 2025-05-13 о 19.04.22_ca39d379](https://europe1.discourse-cdn.com/arduino/original/4X/5/1/7/51713b753efeb176a710418276d12ef36eb21c92.jpeg)  
 ![Знімок екрана 2025-05-13 185549](https://europe1.discourse-cdn.com/arduino/original/4X/8/c/a/8ca4462041ee451d796bc20f33625fe58aebe350.png)  
 ![Зображення WhatsApp, дата_ 2025-05-13 о 18.55.36_b8708f7e](https://europe1.discourse-cdn.com/arduino/original/4X/7/0/b/70bfc7c0bac52399c271872454aed93bd30b0752.jpeg)  
png)

Hello everyone who want to help me i have been trying to de bug my thermo relay im using chinese arduini uno atmega328 core 10 10kom resistors 100kom termistor and 5 vdc relay.  
my scheme is working but when im trying to make relay turn off after the temperature reaaches 200 degreee celsium but it doesnt show temperature correctly (i know how to fix that) and when it reaches something around 120~150 degree celsium the arduino uno takes 5~10 sec and that is very anoing i need it to turn off as fast as posible and turn back on when temperature drops 5 degree lover the set temp.

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<div class="post-metadata">

**Author:** ![Railroader](https://dub1.discourse-cdn.com/arduino/user_avatar/forum.arduino.cc/railroader/32/274550_2.png) [@Railroader](https://forum.arduino.cc/u/Railroader)\
**Post date:** [May 13, 2025, 6:28pm UTC](https://forum.arduino.cc/t/termo-relay-on-arduino-i-need-help/1381244/3 "2025-05-13T18:28:09Z")

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Please read and use this link: [How to get the best out of this forum - Projects / General Guidance - Arduino Forum](https://forum.arduino.cc/t/how-to-get-the-best-out-of-this-forum/681308)

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**Author:** ![PaulRB](https://dub1.discourse-cdn.com/arduino/user_avatar/forum.arduino.cc/paulrb/32/216330_2.png) [@PaulRB](https://forum.arduino.cc/u/PaulRB)\
**Post date:** [May 13, 2025, 6:38pm UTC](https://forum.arduino.cc/t/termo-relay-on-arduino-i-need-help/1381244/4 "2025-05-13T18:38:36Z")

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> [@ardduino\_noob](#):
>
> im trying to make relay turn off after the temperature reaaches 200 degreee celsium

Your code is checking for 270, not 200.

> [@ardduino\_noob](#):
>
> it doesnt show temperature correctly (i know how to fix that)

How is it incorrect and how will you fix that?

> [@ardduino\_noob](#):
>
> when it reaches something around 120~150 degree celsium the arduino uno takes 5~10 sec

5~10 seconds to do what?

There is no test in your code except the 270 test.

Perhaps your English is so full of mistakes because you are very angry and frustrated. If so, please take time to become calm before you post again. If you are calm now, then maybe you should use an on-line translator so that you do not have to write in English.

Please read the forum guide before you post again.

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<div class="post-metadata">

**Author:** ![ardduino\_noob](https://dub1.discourse-cdn.com/arduino/user_avatar/forum.arduino.cc/ardduino_noob/32/1179114_2.png) [@ardduino\_noob](https://forum.arduino.cc/u/ardduino_noob)\
**Post date:** [May 13, 2025, 7:10pm UTC](https://forum.arduino.cc/t/termo-relay-on-arduino-i-need-help/1381244/5 "2025-05-13T19:10:48Z")

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im sorry im only learning english so its not the best  
it takes 5 to 10 update the temp data

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<div class="post-metadata">

**Author:** ![ardduino\_noob](https://dub1.discourse-cdn.com/arduino/user_avatar/forum.arduino.cc/ardduino_noob/32/1179114_2.png) [@ardduino\_noob](https://forum.arduino.cc/u/ardduino_noob)\
**Post date:** [May 13, 2025, 7:12pm UTC](https://forum.arduino.cc/t/termo-relay-on-arduino-i-need-help/1381244/6 "2025-05-13T19:12:37Z")

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it is checking for 270 because i reset the thing that make it show right so for now it is 270 but 200 in reality

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<div class="post-metadata">

**Author:** ![ardduino\_noob](https://dub1.discourse-cdn.com/arduino/user_avatar/forum.arduino.cc/ardduino_noob/32/1179114_2.png) [@ardduino\_noob](https://forum.arduino.cc/u/ardduino_noob)\
**Post date:** [May 13, 2025, 7:16pm UTC](https://forum.arduino.cc/t/termo-relay-on-arduino-i-need-help/1381244/7 "2025-05-13T19:16:52Z")

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![Знімок екрана 2025-05-13 201354](https://europe1.discourse-cdn.com/arduino/original/4X/d/e/4/de421610ce8cc14b15b096527b96216943b50c54.png)  
i swap temp=temp 273.15 to 330 on line 7 and it makes it display 200 degree but it shows incorect temp if it below 180 and more that 240  
and i swaped on lin 13 temp from 270 to 200

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<div class="post-metadata">

**Author:** ![PaulRB](https://dub1.discourse-cdn.com/arduino/user_avatar/forum.arduino.cc/paulrb/32/216330_2.png) [@PaulRB](https://forum.arduino.cc/u/PaulRB)\
**Post date:** [May 13, 2025, 7:37pm UTC](https://forum.arduino.cc/t/termo-relay-on-arduino-i-need-help/1381244/8 "2025-05-13T19:37:16Z")

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I asked you to read the forum guide before you replied and it is clear that you have not done that.

Good luck with your project.

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<div class="post-metadata">

**Author:** ![UKHeliBob](https://dub1.discourse-cdn.com/arduino/user_avatar/forum.arduino.cc/ukhelibob/32/215663_2.png) [@UKHeliBob](https://forum.arduino.cc/u/UKHeliBob)\
**Post date:** [May 13, 2025, 7:42pm UTC](https://forum.arduino.cc/t/termo-relay-on-arduino-i-need-help/1381244/9 "2025-05-13T19:42:14Z")

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Please follow the advice given in the link below when posting code, in particular the section entitled 'Posting code and common code problems'  
  
Use **code tags** (the \< CODE/ \> icon above the compose window)&nbsp;to make it easier to read and copy for examination   
  
[https://forum.arduino.cc/t/how-to-get-the-best-out-of-this-forum](https://forum.arduino.cc/t/how-to-get-the-best-out-of-this-forum)

Please post your full sketch, using code tags when you do

Posting your code using code tags prevents parts of it being interpreted as HTML coding and makes it easier to copy for examination

In my experience the easiest way to tidy up the code and add the code tags is as follows

Start by tidying up your code by using Tools/Auto Format in the IDE to make it easier to read. Then use Edit/Copy for Forum and paste what was copied in a new reply. Code tags will have been added to the code to make it easy to read in the forum thus making it easier to provide help.

It is also helpful to post error messages in code tags as it makes it easier to scroll through them and copy them for examination

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<div class="post-metadata">

**Author:** ![ardduino\_noob](https://dub1.discourse-cdn.com/arduino/user_avatar/forum.arduino.cc/ardduino_noob/32/1179114_2.png) [@ardduino\_noob](https://forum.arduino.cc/u/ardduino_noob)\
**Post date:** [May 13, 2025, 8:32pm UTC](https://forum.arduino.cc/t/termo-relay-on-arduino-i-need-help/1381244/10 "2025-05-13T20:32:00Z")

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![image](https://europe1.discourse-cdn.com/arduino/original/4X/7/1/8/718ec5ce4ed2ec048caa4af940a19058a10e9aab.png)  
the relay on scheme is different but connected the same way

```arduino
#define RELAY1 9
double Thermister(int data) {
  double temp;
  temp = log(10000.0 * ((1024.0 / data - 1)));
  temp = 1 / (0.001129148 + (0.000234125 + (0.0000000876741 * temp * temp)) * temp);
  temp = temp - 330;
  Serial.println(" ");
  Serial.print(temp);
  Serial.print(" Celcius");
  Serial.println("..................................");
  if (temp >= 200) {
    digitalWrite(RELAY1, LOW);
    Serial.println("heating off");
  } else {
    digitalWrite(RELAY1, HIGH);
    Serial.println("heating on");
  }
}

void setup() {
  Serial.begin(9600);
  pinMode(RELAY1, OUTPUT);
  digitalWrite(RELAY1, LOW);
}
int i;
void loop() {
  i = analogRead(A0);
  Thermister(i);
  delay(1000);
}

```

im using arduino uno, 10 10kom resistors,breadboard, TONGLING jqc-3ff-s-z relay,100kom thermistor

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<div class="post-metadata">

**Author:** ![Wawa](https://dub1.discourse-cdn.com/arduino/user_avatar/forum.arduino.cc/wawa/32/1211303_2.png) [@Wawa](https://forum.arduino.cc/u/Wawa)\
**Post date:** [May 13, 2025, 8:32pm UTC](https://forum.arduino.cc/t/termo-relay-on-arduino-i-need-help/1381244/11 "2025-05-13T20:32:45Z")

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Which sensor are we talking about.  
I think I see some black tube, but I also see clixons (thermal switches).  
The string of 10k resistors might be wrong for a 100k thermistor.  
We normally use a pull up resistor value of the thermistor value **at the temp of interrest**.  
A 10k pull up resistor could be better suited for a 100k thermistor at those high temps.  
Leo..

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<div class="post-metadata">

**Author:** ![ardduino\_noob](https://dub1.discourse-cdn.com/arduino/user_avatar/forum.arduino.cc/ardduino_noob/32/1179114_2.png) [@ardduino\_noob](https://forum.arduino.cc/u/ardduino_noob)\
**Post date:** [May 13, 2025, 8:38pm UTC](https://forum.arduino.cc/t/termo-relay-on-arduino-i-need-help/1381244/12 "2025-05-13T20:38:38Z")

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i didnt have the right resistors i connected 10 10kom resistors to get 100kom

> [@Wawa](#):
>
> I see some black tube

> [@Wawa](#):
>
> Which sensor are we talking about.

what do you mean?

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<div class="post-metadata">

**Author:** ![Wawa](https://dub1.discourse-cdn.com/arduino/user_avatar/forum.arduino.cc/wawa/32/1211303_2.png) [@Wawa](https://forum.arduino.cc/u/Wawa)\
**Post date:** [May 13, 2025, 11:08pm UTC](https://forum.arduino.cc/t/termo-relay-on-arduino-i-need-help/1381244/13 "2025-05-13T23:08:34Z")

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> [@ardduino\_noob](#):
>
> what do you mean?

Post#1 shows a 2-wire sensor, post#10 shows a 3-wire sensor.  
So what do you have.

> [@ardduino\_noob](#):
>
> to get 100kom

Why 100k.  
Using 100k with a 100k thermistor is a bad idea when you need to measure high temps.  
Leo..

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<div class="post-metadata">

**Author:** ![ardduino\_noob](https://dub1.discourse-cdn.com/arduino/user_avatar/forum.arduino.cc/ardduino_noob/32/1179114_2.png) [@ardduino\_noob](https://forum.arduino.cc/u/ardduino_noob)\
**Post date:** [May 14, 2025, 5:46am UTC](https://forum.arduino.cc/t/termo-relay-on-arduino-i-need-help/1381244/14 "2025-05-14T05:46:52Z")

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I have 2 wire sensor which will get replased with different 2wire 100kom

> [@Wawa](#):
>
> Using 100k with a 100k thermistor is a bad idea when you need to measure high temps.

So what should i use then?

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<div class="post-metadata">

**Author:** ![ardduino\_noob](https://dub1.discourse-cdn.com/arduino/user_avatar/forum.arduino.cc/ardduino_noob/32/1179114_2.png) [@ardduino\_noob](https://forum.arduino.cc/u/ardduino_noob)\
**Post date:** [May 14, 2025, 6:25am UTC](https://forum.arduino.cc/t/termo-relay-on-arduino-i-need-help/1381244/15 "2025-05-14T06:25:03Z")

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![Знімок екрана 2025-05-14 072218](https://europe1.discourse-cdn.com/arduino/original/4X/d/b/f/dbf360de0ad399919d8ea761a2210a42b4726a32.png)  
I apologize i made a mistake in diagram the termistor was wired wrong way

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<div class="post-metadata">

**Author:** ![Wawa](https://dub1.discourse-cdn.com/arduino/user_avatar/forum.arduino.cc/wawa/32/1211303_2.png) [@Wawa](https://forum.arduino.cc/u/Wawa)\
**Post date:** [May 14, 2025, 7:27am UTC](https://forum.arduino.cc/t/termo-relay-on-arduino-i-need-help/1381244/16 "2025-05-14T07:27:48Z")

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> [@ardduino\_noob](#):
>
> So what should i use then?

Did you actually read my replies?  
Leo..

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<div class="post-metadata">

**Author:** ![jim-p](https://dub1.discourse-cdn.com/arduino/user_avatar/forum.arduino.cc/jim-p/32/922840_2.png) [@jim-p](https://forum.arduino.cc/u/jim-p)\
**Post date:** [May 14, 2025, 9:47am UTC](https://forum.arduino.cc/t/termo-relay-on-arduino-i-need-help/1381244/17 "2025-05-14T09:47:33Z")

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Is that the correct temperature formula for the thermister you have or is it just something you copied off the internet?

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<div class="post-metadata">

**Author:** ![TomGeorge](https://dub1.discourse-cdn.com/arduino/user_avatar/forum.arduino.cc/tomgeorge/32/215261_2.png) [@TomGeorge](https://forum.arduino.cc/u/TomGeorge)\
**Post date:** [May 14, 2025, 9:59am UTC](https://forum.arduino.cc/t/termo-relay-on-arduino-i-need-help/1381244/18 "2025-05-14T09:59:07Z")

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Hi, @ardduino_noob  
Welcome to the forum  
Can you please tell us what your native language is?

> [@ardduino\_noob](#):
>
> I apologize i made a mistake in diagram the termistor was wired wrong way

Can you please post a copy of your circuit, a picture of a hand drawn circuit in jpg, png?  
Hand drawn and photographed is perfectly acceptable.  
Please include ALL hardware, power supplies, component names and pin labels.

For the relay, draw a box and label the points that the wire go into it.

 ![image](https://europe1.discourse-cdn.com/arduino/original/4X/7/4/a/74a100701186dc856a2846cd68289b16af962a65.png)  
A similar box for the UNO.

Please forget about using Fritzy diagrams.

Tom.... 😃 👍 ☕ 🇦🇺

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<div class="post-metadata">

**Author:** ![ardduino\_noob](https://dub1.discourse-cdn.com/arduino/user_avatar/forum.arduino.cc/ardduino_noob/32/1179114_2.png) [@ardduino\_noob](https://forum.arduino.cc/u/ardduino_noob)\
**Post date:** [May 14, 2025, 11:05am UTC](https://forum.arduino.cc/t/termo-relay-on-arduino-i-need-help/1381244/19 "2025-05-14T11:05:44Z")

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I dont understand what is pull up resistor

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<div class="post-metadata">

**Author:** ![ardduino\_noob](https://dub1.discourse-cdn.com/arduino/user_avatar/forum.arduino.cc/ardduino_noob/32/1179114_2.png) [@ardduino\_noob](https://forum.arduino.cc/u/ardduino_noob)\
**Post date:** [May 14, 2025, 11:09am UTC](https://forum.arduino.cc/t/termo-relay-on-arduino-i-need-help/1381244/20 "2025-05-14T11:09:59Z")

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Ukrainian  
I cant send a picnow im not at home  
im using arduino uno, 10 10kom resistors,breadboard, TONGLING jqc-3ff-s-z relay,100kom thermistor

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<div class="post-metadata">

**Author:** ![ardduino\_noob](https://dub1.discourse-cdn.com/arduino/user_avatar/forum.arduino.cc/ardduino_noob/32/1179114_2.png) [@ardduino\_noob](https://forum.arduino.cc/u/ardduino_noob)\
**Post date:** [May 14, 2025, 11:10am UTC](https://forum.arduino.cc/t/termo-relay-on-arduino-i-need-help/1381244/21 "2025-05-14T11:10:54Z")

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I looked it up and after adapted for my use

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