Slim Node Si7021 sensor example

  • Hero Member

    @jacikaas that's the way to go. The sensebender sketch contains some rather nice best practices for low power. You best replace the si library with the one in the MySensors examples on github.

  • @AWI I try to replace library from this one to this one

    to work it I need to return variable name from:

      int humidity = data.humidityBasisPoints;


      int humidity = data.humidityPercent;

    I think this library was updated, so it is not suitable for this one code. Now I test it again and everything looks fine:
    0_1471719934242_chart (1).jpeg

    Temperature and humidity node unregister or stop working repeatedly for about 2 hours (2h25min, 2.20, 1.50...). But after that it start to send data again, for some time and then goes around again. 🙂 I will try to understand why it happening too.

  • I am trying to build the code using the HTU21D sensors. This built fine under 1.4 and 1.5 but now under v2 of MySensors I am getting this error:

    C:\Users\wergeld\Documents\Arduino\SlimNodeSi7021\SlimNodeSi7021.ino:4:24: fatal error: MySensor.h: No such file or directory
     #include <MySensor.h>  
    compilation terminated.
    exit status 1
    Error compiling for board APM Optiboot internal 1MHz noBOD 9600baud.

    Okay, so I change my reference to:

    #include <MySensors.h>

    And I get this lovely error:

    In file included from C:\Users\wergeld\Documents\Arduino\SlimNodeSi7021\SlimNodeSi7021.ino:4:0:
    C:\Users\wergeld\Documents\Arduino\libraries\MySensors-master/MySensors.h:287:4: error: #error No forward link or gateway feature activated. This means nowhere to send messages! Pretty pointless.
       #error No forward link or gateway feature activated. This means nowhere to send messages! Pretty pointless.
    exit status 1
    Error compiling for board APM Optiboot internal 1MHz noBOD 9600baud.

    So, other than slamming my head against my desk how can I solve this?

  • Well, I solved it by modifying the code to 2.0 spec. Good lord I need sleep. 😧
    Working on debugging temp outputs now to Ethernet Gateway running on my Uno. Or I will sleep...

  • Okay, I now have a soldered node and serial gateway setup to my laptop for testing. It presents the sensor node! The name and available sensors is correct. Howevr, it never sends any message payload with temp/hum or battery values. I am using the HTU21D without soldering those 3 pads on it together. I need to get myself a 3.3v FTDI cable so I can serially debug I guess. But, still! Progress.

  • After soldering the 3 pads on the HTU21D I am now reading data and it is being sent to my test serial gateway. Need to measure current usage but at least it is functional.

  • Okay, seeing something odd. The force transmit does not appear to be working.
    Here is my current sketch:

    #define MY_RADIO_NRF24
    #include <MyConfig.h>
    #include <MySensors.h>
    /* Sketch with Si7021 and battery monitoring.
    by m26872, 20151109 
    //#include <MySensors.h>  
    #include <Wire.h>
    #include <SparkFunHTU21D.h>
    #include <SPI.h>
    #include <RunningAverage.h>
    //#define DEBUG
    #ifdef DEBUG
    #define DEBUG_SERIAL(x) Serial.begin(x)
    #define DEBUG_PRINT(x) Serial.print(x)
    #define DEBUG_PRINTLN(x) Serial.println(x)
    #define DEBUG_SERIAL(x)
    #define DEBUG_PRINT(x) 
    #define DEBUG_PRINTLN(x) 
    #define NODE_ID 132             // <<<<<<<<<<<<<<<<<<<<<<<<<<<   Enter Node_ID
    #define CHILD_ID_TEMP 0
    #define CHILD_ID_HUM 1
    // #define SLEEP_TIME 15000 // 15s for DEBUG
    #define SLEEP_TIME 300000   // 5 min
    #define FORCE_TRANSMIT_CYCLE 36  // 5min*12=1/hour, 5min*36=1/3hour 
    #define BATTERY_REPORT_CYCLE 2880   // Once per 5min   =>   12*24*7 = 2016 (one report/week)
    #define VMIN 1900
    #define VMAX 3300
    #define HUMI_TRANSMIT_THRESHOLD 3.0  // THRESHOLD tells how much the value should have changed since last time it was transmitted.
    #define AVERAGES 2
    int batteryReportCounter = BATTERY_REPORT_CYCLE - 1;  // to make it report the first time.
    int measureCount = 0;
    float lastTemperature = -100;
    int lastHumidity = -100;
    RunningAverage raHum(AVERAGES);
    HTU21D humiditySensor;
    //MySensor gw;
    MyMessage msgTemp(CHILD_ID_TEMP,V_TEMP); // Initialize temperature message
    MyMessage msgHum(CHILD_ID_HUM,V_HUM);
    void presentation()  
      sendSketchInfo("HTU21D", "1.0"); 
      present(CHILD_ID_TEMP, S_TEMP);   // Present sensor to controller
      present(CHILD_ID_HUM, S_HUM);
    void setup() {
      DEBUG_SERIAL(9600);    // <<<<<<<<<<<<<<<<<<<<<<<<<< Note BAUD_RATE in MySensors.h
      DEBUG_PRINTLN("Serial started");
      DEBUG_PRINT("Voltage: ");
      DEBUG_PRINTLN(" mV");
      DEBUG_PRINT("Internal temp: ");
      DEBUG_PRINT(GetInternalTemp()); // Probably not calibrated. Just to print something.
      DEBUG_PRINTLN(" *C");
      delay(500); // Allow time for radio if power useed as reset
      //sendSketchInfo("HTU21D", "1.0"); 
      //present(CHILD_ID_TEMP, S_TEMP);   // Present sensor to controller
      //present(CHILD_ID_HUM, S_HUM);
      DEBUG_PRINT("Node and "); DEBUG_PRINTLN("2 children presented.");
    void loop() { 
      measureCount ++;
      batteryReportCounter ++;
      bool forceTransmit = false;
      if (measureCount > FORCE_TRANSMIT_CYCLE) {
        forceTransmit = true; 
      // Read and print internal temp
      float temperature0 = static_cast<float>(static_cast<int>((GetInternalTemp()+0.5) * 10.)) / 10.;
      DEBUG_PRINT("Internal Temp: "); DEBUG_PRINT(temperature0); DEBUG_PRINTLN(" *C");        
      // Check battery
      if (batteryReportCounter >= BATTERY_REPORT_CYCLE) {
        long batteryVolt = readVcc();
        DEBUG_PRINT("Battery voltage: "); DEBUG_PRINT(batteryVolt); DEBUG_PRINTLN(" mV");
        uint8_t batteryPcnt = constrain(map(batteryVolt,VMIN,VMAX,0,100),0,255);   
        DEBUG_PRINT("Battery percent: "); DEBUG_PRINT(batteryPcnt); DEBUG_PRINTLN(" %");
        batteryReportCounter = 0;
    // function for reading Vcc by reading 1.1V reference against AVcc. Based from
    // To calibrate reading replace 1125300L with scale_constant = internal1.1Ref * 1023 * 1000, where internal1.1Ref = 1.1 * Vcc1 (per voltmeter) / Vcc2 (per readVcc() function) 
    long readVcc() {
      // set the reference to Vcc and the measurement to the internal 1.1V reference
      ADMUX = _BV(REFS0) | _BV(MUX3) | _BV(MUX2) | _BV(MUX1);
      delay(2); // Wait for Vref to settle
      ADCSRA |= _BV(ADSC); // Start conversion
      while (bit_is_set(ADCSRA,ADSC)); // measuring
      uint8_t low  = ADCL; // must read ADCL first - it then locks ADCH  
      uint8_t high = ADCH; // unlocks both
      long result = (high<<8) | low;
      result = 1125300L / result; // Calculate Vcc (in mV); 1125300 = 1.1*1023*1000
      return result; // Vcc in millivolts
    // function for reading internal temp. From 
    double GetInternalTemp(void) {  // (Both double and float are 4 byte in most arduino implementation)
      unsigned int wADC;
      double t;
      // The internal temperature has to be used with the internal reference of 1.1V. Channel 8 can not be selected with the analogRead function yet.
      ADMUX = (_BV(REFS1) | _BV(REFS0) | _BV(MUX3));   // Set the internal reference and mux.
      ADCSRA |= _BV(ADEN);  // enable the ADC
      delay(20);            // wait for voltages to become stable.
      ADCSRA |= _BV(ADSC);  // Start the ADC
      while (bit_is_set(ADCSRA,ADSC));   // Detect end-of-conversion
      wADC = ADCW;   // Reading register "ADCW" takes care of how to read ADCL and ADCH.
      t = (wADC - 88.0 ) / 1.0;   // The default offset is 324.31.
      return (t);   // The returned temperature in degrees Celcius.
     * * Sends temperature and humidity from Si7021 sensor
     * Parameters
     * - force : Forces transmission of a value (even if it's the same as previous measurement)
    void sendTempHumidityMeasurements(bool force) {
      bool tx = force;
      float temperature = humiditySensor.readTemperature();
      DEBUG_PRINT("T: ");DEBUG_PRINTLN(temperature);
      float diffTemp = abs(lastTemperature - temperature);
      DEBUG_PRINT(F("TempDiff :"));DEBUG_PRINTLN(diffTemp);
      if (diffTemp > TEMP_TRANSMIT_THRESHOLD || tx) {
        lastTemperature = temperature;
        measureCount = 0;
        DEBUG_PRINTLN("T sent!");
      int humidity = humiditySensor.readHumidity();
      DEBUG_PRINT("H: ");DEBUG_PRINTLN(humidity);
      humidity = raHum.getAverage();  // MA sample imply reasonable fast sample frequency
      float diffHum = abs(lastHumidity - humidity);
      DEBUG_PRINT(F("HumDiff  :"));DEBUG_PRINTLN(diffHum); 
      if (diffHum > HUMI_TRANSMIT_THRESHOLD || tx) {
        lastHumidity = humidity;
        measureCount = 0;
        DEBUG_PRINTLN("H sent!");

    I am at 1+ hours since last transmission.

  • Hardware Contributor

    @wergeld It looks like it's set to 3 hrs.

  • @m26872
    Indeed it does. Just was throwing me off with the wording. I read it as "1/2 hour" or "1/3 hour". So far I am prepping up more nodes. Have 4 more 328s to programs and build out. I am thinking at the end I will have:

    1. Gateway (serial or the direct connect nrf+ once it supports v2)
    2. Temp/Hum node using HTU21D for back porch sending every 5 minutes and force send every 30 minutes.
    3. Temp/Hum node using HTU21D inside using same send times.
    4. Parking sensor in garage hardwired to mains.
      5 & 6 I am not sure yet.

    Lots of fun so far.

  • I am seeing 5.0 ΞA at sleep and 12.4 mA when transmitting. Seems kind of high. I did the poor man's test as well - put an LED across the HTU21D power pins and it lit up. Same when I did it across the nrf's power pins. Shouldn't the MySensors code turn off the power rails during sleep?

  • Hardware Contributor


    No, the powerrails are not turned off, just the devices themselves.

    5uA during sleep is about right. The 12.4mA during transmit is also normal, but the transmit time should be very short, so on average the total consumption of power will be low.

  • @GertSanders Excellent! I was hoping I hadn't wired it up wrong. So far the 2 nodes have been flawless for the past 3 days. Next step is to await the direct attached NRF serial gateway to be v2 compatible. Been following along with this thread. Looks like we are getting closer! I have 2 RPis (one a first gen B and the other a Pi2 B ) with this adapter by ceech:

  • Hi everyone,

    First thanks for sharing. I love this slim node. But I am facing some issues I did not success to debug. So I use the code shared here for mysensors 2. I try with the mysensors exemple library (did not work at all). I try with the which worked (at least for getting separately temperature and humidity and using the example file) on an arduino nano. But when I run this sensor with the slim node (red, boot loader 8mhz) and the code (for 2.0.0) I always get -46.85 for temperature and 118 for humidity. Otherwise the radio work normally.

    Winter is coming and I don't know what I could do anymore. Thanks to share you idea on this.

    With the example code I use on the nano. I get with the slim node:

    T: -46.85
    H: 118
    device ID: 50

    With Arduino nano:

    T: 24.34
    H: 43
    device ID: 50

  • Why actually my device id is 50 ? for what 50 stands !?!?!

  • Hardware Contributor

    @clempat Please post your sketch and maybe some hardware photo or diagram too.

  • @m26872 Sure I can do that. So I simplified the code to only focus on the si7021.

    Here it is:

    And there the photo:





  • Hardware Contributor

    @clempat Don't think I can help you. Maybe clock related. What voltages do you use on Nano and Slim respectively? Do you have multiple parts to try with and get the same result? Why do you include and start wire.h, isn't already in Si7021.h ? My guess on "device Id 50" is that it's just a chinese clone reply.
    Photos look nice btw. 👍

  • @m26872 Thank you. Yes I wanted to try with a pro mini 8Mhz but I need to prepare the pin 4 and 5. I will keep inform when I do it this week end.

    Thanks for the picture but with this nice setup it is difficult to make it bad :)...

    I includes wire.h like in the exemple in but of course after I tried without. The nano was directly connected to usb and the slim through 3,3V USB to serial.

  • Ok with the arduino micro 8Mhz all works good too.

    T: 20.29
    H: 54
    device ID: 50

  • So sad I still not getting it working with the slim node 😞 !!! Always same result either with internal 1mhz or 8mhz...