Picture 1

Picture 2

• Voltage of +5V-line: +5,07 V at Grove-connector and at end of 20m-cable = ok = no voltage drop (measured with DMM)
• Signal-shape of 1-wire-signal-line: see attached photo below = ok, but seee comments in photo (measured with oscilloscope Sony/Tektronix 335)

Nice work so far, any chance of some photo's?

NB: The used cable is a YM-L3G 0,75mm2 installation cable. I know, it is much to massive for the signal current, but it is easier and more robust for later installation.

In the meantime I am giving you some information in this forum:

The planned project:
Logging of data of the house heating system for "years" for diagnostical and statistical purposes

Functions needed in detail:

• measuring of about 10 temprature sensors, environmant data, oil burner run time, +++
• getting date and time from webserver via WLAN
• use buttons for start/stop of measurement, single measurement, +++
• show actual data on Lcd of M5Stack and monitor (if connected)
• write all data to SD-card
• use LED's of M5Stack-Fire for heartbeat, measurement in progress, waiting for next measurement slot, WLAN connection, +++
• optional: sending data to PC via WLAN to import them into Excel for analysis (or transfering the data from SD-card to PC via a card-reader)
• optional:Webserver for live-data and SD-card-data
• +++, tbd

... puh..., I fear, this will be long way to go (at least for me...).

The software (up to now, this is all I have so far - I wanted to start with testing and building up some experiences of using the DS18B20 sensors connected to a M5Stack-Fire):

/*
 * Software for basic tests of temperature measurement on M5Stack-FIRE with several DS18B20 temperature sensors
 * 1-wire-pull-up resistor = 2 kohm  (did not not work with 4,7 kohm !!!!
 * modified by GRELM; 2019-06-16
 */

  #include <M5Stack.h>
  #include <OneWire.h>
  #include <DallasTemperature.h>

  #define ONE_WIRE_BUS 26  //DS18B20 on Grove B corresponds to GPIO26 on ESP32

  OneWire oneWire(ONE_WIRE_BUS);
  DallasTemperature DS18B20(&oneWire);

/*  Resolution of DS18B20 temperatur measurement = power-on-default = 12 bit = 0.0625 C
   *9-bit resolution --> 93.75 ms
   *10-bit resolution --> 187.5 ms
   *11-bit resolution --> 375 ms
   *12-bit resolution --> 750 ms
*/ 
  String monitorstring = "";  

  void setup() {
    M5.begin();
    M5.Lcd.setTextColor(TFT_WHITE,TFT_BLACK);  
    M5.Lcd.setTextSize(2);
    M5.Lcd.clear();  //just to make sure...

    Serial.println(); // to separate data from booting output
    monitorstring = "Date;Time;A;B;C;D;E;F;G;H;I;J;"; // up to 10 data-colums fpr up to 10 sensors
    Serial.println(monitorstring);  // Monitor Headline for Excel Headline
  }
  
  void loop() {
    float celsius;
    float fahrenheit;

    monitorstring = "Date;Time";  // change to realtime date and time of M5Stack (later)
    
    DS18B20.begin();
    int count = DS18B20.getDS18Count();  //check for number of connected sensors

//    M5.Lcd.clear();    //clearing causes flickering of Lcd-display, looks nicer without
    M5.Lcd.setCursor(0,0);
    M5.Lcd.print("Devices found: ");
    M5.Lcd.print(count);
    M5.Lcd.println(" DS18B20");

    if (count > 0) {
    DS18B20.requestTemperatures();
    for (int i=0; i < count; i++) {
      String m5stackstring = "Sensor ";
 
      celsius = DS18B20.getTempCByIndex(i);

      m5stackstring = m5stackstring + String(i) + String(": ") + String(celsius,4) + String(" C     ");  
      M5.Lcd.println(m5stackstring);  // 1 line per sensor on M5Stack Lcd
    
      monitorstring = monitorstring + String(";") + String(celsius,4);  // ";" is Excel compatibel separator
 
    }
    Serial.println(monitorstring);  // 1 line for all measurements on serial monitor
    }
    delay(500); //Measuremnt interval
  }

Please and Thank you
AJB2K3.