About DS18B20 onewire.

    1. Anyone know how many ds18b20 you can connect to a MySensors sketch?
      This sketch saying maximum 16, https://www.mysensors.org/build/temp.

    2. Lets say you have 3 sensors and sending them to e.g. Domoticz.
      Sensor A=15 °C
      Sensor B=25 °C
      Sensor C=35 °C
      If I understand the sketch correct, it will first search for connected sensors and then send one by one to Controller.
      I will create a Device called "A" in Controller and will receive value from sensor A to Device A, same for B and C.
      What happen if sensor B fails or I disconnect it.
      Will sensor C be the new sensor B?

  • I have now tested this and the answer is YES, if B disconnects C will be the new B

  • I have modify the sketch so now if sensor B is disconnected A will be A and C will be C, as soon as B is connected again it will send the values again.

     * The MySensors Arduino library handles the wireless radio link and protocol
     * between your home built sensors/actuators and HA controller of choice.
     * The sensors forms a self healing radio network with optional repeaters. Each
     * repeater and gateway builds a routing tables in EEPROM which keeps track of the
     * network topology allowing messages to be routed to nodes.
     * Created by Henrik Ekblad <henrik.ekblad@mysensors.org>
     * Copyright (C) 2013-2015 Sensnology AB
     * Full contributor list: https://github.com/mysensors/Arduino/graphs/contributors
     * Documentation: http://www.mysensors.org
     * Support Forum: http://forum.mysensors.org
     * This program is free software; you can redistribute it and/or
     * modify it under the terms of the GNU General Public License
     * version 2 as published by the Free Software Foundation.
     * Example sketch showing how to send in DS1820B OneWire temperature readings back to the controller
     * http://www.mysensors.org/build/temp
    #include <MySensor.h>  
    #include <SPI.h>
    #include <DallasTemperature.h>
    #include <OneWire.h>
    #define COMPARE_TEMP 0 // Send temperature only if changed? 1 = Yes 0 = No
    #define ONE_WIRE_BUS 3 // Pin where dallase sensor is connected 
    #define MAX_ATTACHED_DS18B20 16
    unsigned long SLEEP_TIME = 3000; // Sleep time between reads (in milliseconds)
    OneWire oneWire(ONE_WIRE_BUS); // Setup a oneWire instance to communicate with any OneWire devices (not just Maxim/Dallas temperature ICs)
    DallasTemperature sensors(&oneWire); // Pass the oneWire reference to Dallas Temperature. 
    byte D[3][8] = {
    { 0x28, 0xB1, 0x47, 0xB4, 0x04, 0x00, 0x00, 0x97 },
    { 0x28, 0xFF, 0x53, 0x78, 0x63, 0x15, 0x02, 0xC9 },
    { 0x28, 0xFF, 0xCD, 0x06, 0x52, 0x04, 0x00, 0x80 }
    MySensor gw;
    float lastTemperature[MAX_ATTACHED_DS18B20];
    int numSensors=0;
    boolean receivedConfig = false;
    boolean metric = true; 
    // Initialize temperature message
    MyMessage msg(0,V_TEMP);
    void setup()  
      // Startup up the OneWire library
      // requestTemperatures() will not block current thread
      // Startup and initialize MySensors library. Set callback for incoming messages. 
      // Send the sketch version information to the gateway and Controller
      gw.sendSketchInfo("Temperature Sensor", "1.1");
      // Fetch the number of attached temperature sensors  
      //numSensors = sensors.getDeviceCount();
      // Present all sensors to controller
      for (int i=0; i<3 && i<MAX_ATTACHED_DS18B20; i++) {   
         gw.present(i, S_TEMP);
    void loop()     
      // Process incoming messages (like config from server)
      // Fetch temperatures from Dallas sensors
      // query conversion time and sleep until conversion completed
      int16_t conversionTime = sensors.millisToWaitForConversion(sensors.getResolution());
      // sleep() call can be replaced by wait() call if node need to process incoming messages (or if node is repeater)
      // Read temperatures and send them to controller 
      for (int i=0; i<3 && i<MAX_ATTACHED_DS18B20; i++) {
        // Fetch and round temperature to one decimal
     //   float temperature = static_cast<float>(static_cast<int>((sensors.requestTemperaturesByAddress(D[i])) * 10.)) / 10.;
          float temperature = sensors.getTempC(D[i]);
        // Only send data if temperature has changed and no error
        #if COMPARE_TEMP == 1
        if (lastTemperature[i] != temperature && temperature != -127.00 && temperature != 85.00) {
        if (temperature != -127.00 && temperature != 85.00) {
          // Send in the new temperature
          // Save new temperatures for next compare

    first you need to use this sketch to get the correct addresses for all your DS18B20

    #include <OneWire.h>
    // OneWire DS18S20, DS18B20, DS1822 Temperature Example
    // http://www.pjrc.com/teensy/td_libs_OneWire.html
    // The DallasTemperature library can do all this work for you!
    // http://milesburton.com/Dallas_Temperature_Control_Library
    OneWire  ds(3);  // on pin 10 (a 4.7K resistor is necessary)
    int count=0;
    void setup(void) {
    void loop(void) {
      byte i;
      byte present = 0;
      byte type_s;
      byte data[12];
      byte addr[8];
      float celsius;
      if ( !ds.search(addr)) {
        //Serial.println("No more addresses.");
      //Serial.print("ROM =");
      for( i = 0; i < 8; i++) {
      Serial.print(" 0x");
        //Serial.write(' ');
        //int a = (addr[i], DEC);
        if (addr[i] <= 15){
        Serial.print(addr[i], HEX);
        if (i < 7){
        Serial.print(" },");
      if (OneWire::crc8(addr, 7) != addr[7]) {
          Serial.println("CRC is not valid!");
      // the first ROM byte indicates which chip
      switch (addr[0]) {
        case 0x10:
          //Serial.println("  Chip = DS18S20");  // or old DS1820
          type_s = 1;
        case 0x28:
          //Serial.println("  Chip = DS18B20");
          type_s = 0;
        case 0x22:
          //Serial.println("  Chip = DS1822");
          type_s = 0;
          //Serial.println("Device is not a DS18x20 family device.");
      ds.write(0x44, 1);        // start conversion, with parasite power on at the end
      delay(1000);     // maybe 750ms is enough, maybe not
      // we might do a ds.depower() here, but the reset will take care of it.
      present = ds.reset();
      ds.write(0xBE);         // Read Scratchpad
      //Serial.print("  Data = ");
      //Serial.print(present, HEX);
      //Serial.print(" ");
      for ( i = 0; i < 9; i++) {           // we need 9 bytes
        data[i] = ds.read();
        //Serial.print(data[i], HEX);
        //Serial.print(" ");
      //Serial.print(" CRC=");
      //Serial.print(OneWire::crc8(data, 8), HEX);
      // Convert the data to actual temperature
      // because the result is a 16 bit signed integer, it should
      // be stored to an "int16_t" type, which is always 16 bits
      // even when compiled on a 32 bit processor.
      int16_t raw = (data[1] << 8) | data[0];
      if (type_s) {
        raw = raw << 3; // 9 bit resolution default
        if (data[7] == 0x10) {
          // "count remain" gives full 12 bit resolution
          raw = (raw & 0xFFF0) + 12 - data[6];
      } else {
        byte cfg = (data[4] & 0x60);
        // at lower res, the low bits are undefined, so let's zero them
        if (cfg == 0x00) raw = raw & ~7;  // 9 bit resolution, 93.75 ms
        else if (cfg == 0x20) raw = raw & ~3; // 10 bit res, 187.5 ms
        else if (cfg == 0x40) raw = raw & ~1; // 11 bit res, 375 ms
        //// default is 12 bit resolution, 750 ms conversion time
      celsius = (float)raw / 16.0;
      //Serial.print("  Temperature = ");
      //Serial.println(" Celsius, ");

    you will get the address like this format

    { 0x28, 0xB1, 0x47, 0xB4, 0x04, 0x00, 0x00, 0x97 }

  • it takes about 80 ms for each sensor that you add

  • My test has been running now for 4 days now and it works perfect. Of course it is the same sketch that MySensors is using but I have modified it a little bit.

  • First test with 3 temps is still OK.
    Second test is with 9 temps is still OK.

  • I have now 2 nodes, one with 27 temps, second with 17 temps.

    working with out problems since I started them 1 weeks ago

    I had some problem when adding more sensors, some of them seems not to work together that is why I have 2 nodes

  • How can I get this to work with 2.0 or 2.1.1
    I would so much have to help because I am a beginner

  • @tomasandersson Did some work wrt. this some time ago, sketches for MySensors 2.0+ are available here: https://github.com/rejoe2/MySensors-Dallas-Address-ChildID-Consistency.

    Easiest to use may be the "stored id"-Version, based on a concept of leodesigner. This is designed für max. 20 DS18x20.

  • @rejoe2
    I have now tried the stored ID "version and it works much better than the previous.
    I still get the wrong values sometimes. Wonder if there is control domoticz which mixes the ID.

    0_1490085476002_Skärmavbild 2017-03-21 kl. 09.34.34.png

  • @tomasandersson I really doubt the controller to mix things up, nor the node doing so.
    What are the absolute values of the measured temperatures? The "faulty" values seem to be more or less identical, so this could indicate powering problems or may be related to cabeling or resistor size. Did you stick to the 30 seconds intervall or something else?
    Normally 750ms for conversion should be enought, but official (according to datasheet) seem to be a little longer, so trying to change line 69 may help: conversionTime = 1000 / (1 << (12 - resolution));).

  • @rejoe2
    I will try to change.
    Here is a picture where you see that the sensor ID picks temperature of another sensor0_1490096020397_Skärmavbild 2017-03-21 kl. 12.31.12.png

  • @tomasandersson This really looks strange.
    Some additional remarks:

    • Some values represent also failure codes, beside -127°, 85° (C), which are already filtered out by code I also suspect 0° to be one of these. This is the backgound of me asking above for absolute figures.
    • There seem to be also fake chips on the market; they may have slightly different operation conditions esp. wrt. to timing (if they work at all; I don't have own experience on this).
    • How are your cabeling conditions? I had some troubles when using nRF+PA+LNA modules together with the new (post 2.0.1-) MySensors-libs and more than 5 DS18B20 on one line (non-parasitic mode). This seems to be solved by the use of a small delay between temp-sends (wait(50) or so). With a lot of sensors and long lines and/or star topology, you may have to lower the pullup resistor value (e.g. 3.3k).

  • @rejoe2

    Thanks so much for your help.
    I think you're a little ahead of me in programming. Interesting with time delay between temp sends. How do I create it?

  • @tomasandersson You are welcome!
    I am more feeling as a beginner also in most programming aspects. This is just some sort of copy/pasting in addition with some thoughts on how things may work and reading technical documentation and examples :simple_smile:; most of this is based on leodesigners work here somewhere in the forum (fride monitor). I had a hard time to find solutions working for me, so I'm happy if someone can learn from this.

    Back to the answer: just add a wait(50); as new line 120 (somewhere within the reading/sending for-loop).

  • @rejoe2

    Now I have tried both of the programs. It works much the same. It pops up a fault sometimes.
    Is it difficult to enter a line in the program, says that if the temperature has changed system than - + 5 degrees so it shall not be reported

  • @tomasandersson To me, this really seems to be hardware related, so triple check your wirings first.
    If you really believe this to be a software problem, you may add an additional condition in line 119 with another "&&", (from memory something like abs(lastTemperature[i] - temperature < 5). I would have to test it myself and don't find this reasonable (s.o.), so feel free to finish this part of the job yourself.

  • @rejoe2
    Thank you for helping me in the right direction
    I do not think there is anything wrong with the hardware because I have two identical sets. One to a spa and a heat pump. Maybe I'll try it with less resistance. Now i have 4.8kohm

    I'm now trying with more or less distinction from the former transient temp.
    I will reply when I got it to work.


  • @tomasandersson Just 2 DS18B20 on each line should never cause trouble wrt current draw using a 4.8k resistor and 30 sec. intervals and no additional sensors drawing current from the arduino. If not already in place I would anyhow recommend using 3 wires for operation instead of parasitic mode.
    Anyhow: Best way to identify these chips is using the addresses. Most likely you now are also prepared to do some small editing in sketches?
    "My" array-sketch-version also prints the ID's as array information you need to serial. You may test it and then disable this feature once you have the info for both of your sketches (begin the respecting line with the #define with a "//"). Doing so will definitely eliminate any smallest risk of mixing data...