coin-cell (CR2032) powered temperature sensor

[Moebius Lutching]

There is a TI paper about adding a big capacitor in series with the coin-cell battery to minimize the voltage drop during high-current peaks: http://www.ti.com/lit/wp/swra349/swra349.pdf, also another interesting article related to low-power and CR2032: http://www.low-powerdesign.com/121312-article-extending-battery-life.htm

[fleinze]

@flopp I added the capacitor and put the old battery in. By old battery I mean the one I had replaced a week earlier for a new one. Sensor running smooth since, so great success!

[flopp]

@fleinze
:thumbsup:

[mihai.aldea]

The DS18B20+ is not a great sensor for the battery powered nodes. It has a huge conversion time comparing to others.
9-bit resolution | 93.75 ms | 0.5°C
10-bit resolution | 187.5 ms | 0.25°C
11-bit resolution | 375 ms | 0.125°C
12-bit resolution | 750 ms | 0.0625°C
The last column is the sensor's precision. So unless you're OK with a 0.5°C steps, the simple usage of DS18B20+ will kill your battery a lot faster.
Don't use DHT22, that one is very slow too. BME280 does have a barometric pressure sensor but it's not very fast either.
The best sensor for battery powered nodes is the the Si7021 which is rather old, but is the fastest.

[fleinze]

I put the arduino to sleep during the conversion time, so this is not a big issue. But I agree that the DS18B20 is not the best, but it is widely available. For newer nodes I try to use the Si7021 where possible.

[mihai.aldea]

@fleinze said:

I put the arduino to sleep during the conversion time, so this is not a big issue. But I agree that the DS18B20 is not the best, but it is widely available. For newer nodes I try to use the Si7021 where possible.

It goes without saying that the nodes are in sleep mode between reports. However, the conversion time has a great impact in the cycle math. I won't say that pulling the readings 10 times faster will give you 10 times more time on battery but if you'll get 5 times more time then it's something. Not to mention that the Si7021 works down to 1.9V unlike the DS18B20+ which works down to only 3.0V.

[tango156157]

@fleinze Great work with the CR2032 coin cell temp. sensor. I am trying to do a similar exercise with Si7021 sensors but getting into issues while coding. The examples from other posts around Si7021 adapted for latest MySensor lib seem to get stuck in my IDE giving lot of errors. I have tried getting all the required Header files but still get stuck due to some random error. Is it possible for you to share your code based on CR2032 temp node running on Si7021? Thanks....

[mihai.aldea]

@tango156157, I sometimes get similar errors while compiling the sketches. Mostly because I am still using the MySensors 1.5 library for my legacy network, 2.1.0b for the RFM69 network (working RSSI report) and 2.1.1 for the LoRa network.
Mostly when dealing with MySensors 1.5 and/or older sensors libraries, I find the newer Arduino version to pop all sort of errors. But then I fire up one of the older Arduino IDE versions I have, 1.6.5, 1.6.9 and so on. Eventually one of them compiles the sketch without errors while the newer version don't work. This is far from being a solid solution for these errors, but it gets the job done.
You should try that too, especially if you're using older libraries for your sensors.
You can find them here: https://www.arduino.cc/en/Main/OldSoftwareReleases#previous

[fleinze]

Hi,

this is my code working with 2.1 version. The code is not tidied up, please excuse.

/*
   MySensors-Node for DS18B20 Temperature-Sensors.
   Mysensors.Library-Version 1.6
*/

#define MY_RADIO_NRF24

#define MY_TRANSPORT_UPLINK_CHECK_DISABLED

//#define MY_DEBUG


#include <MySensors.h>
#include <SPI.h>
#include <Wire.h>
#include <SI7021.h>

#define BATT_SENSOR
//#define VCCGND_PINS

#ifdef VCCGND_PINS
const uint8_t GND = A2;
const uint8_t VCC = A3;
#endif

#ifdef BATT_SENSOR
#define REPORT_VOLTAGE
#endif

const unsigned long SLEEP_TIME = 300000; // Sleep time between reads (in milliseconds)

const uint8_t TEMP_TIME = 12; //at least every nth time battery is reported
const uint8_t HUM_TIME = 12;
const uint8_t BATT_TIME = 12; //when also BATT-LEVEL is reportet
const float BATT_100 = 3; //3.3V for CR2032, 3V for 2xAA
const float BATT_0 = 2.2;

SI7021 sensor;

float lastTemperature, lastHum;
uint8_t lastTempSent = 0;//, lastHumSent = 0;
uint8_t numSensors = 0;
boolean receivedConfig = false;
boolean metric = true;
// Initialize temperature message
MyMessage msgTemp(0, V_TEMP);
MyMessage msgHum(0, V_HUM);
#ifdef REPORT_VOLTAGE
MyMessage msgBatt(1, V_VOLTAGE);
#endif
#ifdef BATT_SENSOR
uint8_t battReport = BATT_TIME - 1; //First report at startup
long oldvalue = 0;
#endif


void setup()
{

  #ifdef VCCGND_PINS
  pinMode(VCC, OUTPUT);
  digitalWrite(VCC, HIGH);
  pinMode(GND, OUTPUT);
  digitalWrite(GND, LOW);
  #endif
  
  if (!sensor.begin()) {
    Serial.println("No Sensor found!");
    while (true);
  }
  

}

void presentation() {

  // Send the sketch version information to the gateway and Controller
  sendSketchInfo("TempHumSi7021", "0.1a");

  // Present all sensors to controller
  present(0, S_HUM);
  //present(1, S_HUM);
#ifdef REPORT_VOLTAGE
  present(1, S_MULTIMETER);
#endif
}


void loop()
{
  //delay(2000);//for sensor to start up
  boolean tempsent = false;

  // Fetch temperatures from Dallas sensors
  si7021_thc temphum = sensor.getTempAndRH();

  // Read temperatures and send them to controller
  // Fetch and round temperature to one decimal
  float temperature = (float)(temphum.celsiusHundredths) / 100.0;
  float humidity = (float)(temphum.humidityPercent);
  // Only send data if temperature has changed and no error
  if ((lastTemperature != temperature) || lastHum != humidity || (++lastTempSent >= TEMP_TIME)) {
    // Send in the new temperature
    send(msgTemp.set(temperature, 1));
    send(msgHum.set(humidity, 1));
    lastHum = humidity;
    lastTemperature = temperature;
    lastTempSent = 0;
    tempsent = true;
  }


#ifdef BATT_SENSOR
  if (++battReport >= BATT_TIME && tempsent) {

    //gw.sleep(10);
    long value = readVcc();


    if (value != oldvalue) {
      int percent = (( (float)(value) / 1000 ) - BATT_0) / (BATT_100 - BATT_0) * 100;
      percent = (percent > 100) ? 100 : percent;
      percent = (percent < 0) ? 0 : percent;
      sendBatteryLevel(percent);
#ifdef REPORT_VOLTAGE
      send(msgBatt.set((float)(value) / 1000, 2));
#endif
    }
    oldvalue = value;
    battReport = 0;
  }
#endif
  sleep(SLEEP_TIME);//wake on interrupt or after sleep-time
  //delay(2000);//for sensor to start up
}

long readVcc() {
  // Read 1.1V reference against AVcc
  // set the reference to Vcc and the measurement to the internal 1.1V reference
#if defined(__AVR_ATmega32U4__) || defined(__AVR_ATmega1280__) || defined(__AVR_ATmega2560__)
  ADMUX = _BV(REFS0) | _BV(MUX4) | _BV(MUX3) | _BV(MUX2) | _BV(MUX1);
#elif defined (__AVR_ATtiny24__) || defined(__AVR_ATtiny44__) || defined(__AVR_ATtiny84__)
  ADMUX = _BV(MUX5) | _BV(MUX0);
#elif defined (__AVR_ATtiny25__) || defined(__AVR_ATtiny45__) || defined(__AVR_ATtiny85__)
  ADMUX = _BV(MUX3) | _BV(MUX2);
#else
  ADMUX = _BV(REFS0) | _BV(MUX3) | _BV(MUX2) | _BV(MUX1);
#endif

  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
}```

[tango156157]

@fleinze thanks for sharing your code for Si7021 sensor. I tried compiling but getting below error. Not sure if I am using incorrect header file for Si7021 sensor. I am using MySensors ver 2.1.0 for compiling. Any view? Thanks

C:\Users\abc\AppData\Local\Temp\arduino_modified_sketch_641038\sketch_may14a.ino: In function 'void loop()':

sketch_may14a:91: error: 'si7021_thc' was not declared in this scope

   si7021_thc temphum = sensor.getTempAndRH();

   ^

sketch_may14a:91: error: expected ';' before 'temphum'

   si7021_thc temphum = sensor.getTempAndRH();

              ^

sketch_may14a:95: error: 'temphum' was not declared in this scope

   float temperature = (float)(temphum.celsiusHundredths) / 100.0;

                               ^

Multiple libraries were found for "SI7021.h"
 Used: C:\Users\abc\Documents\Arduino\libraries\SI7021
 Not used: C:\Program Files (x86)\Arduino\libraries\SI7021
exit status 1
'si7021_thc' was not declared in this scope

Insert Code Here

[flopp]

@tango156157
Look you have more than one library for si7021.
Move one library and then try again.
If that doesn't help.

Move back the first library and move the second one, try again and see if that helped

[Edoardo Vogna]

Hello fleinze,
What about this project? Your sensors still working?
I'm trying to build the same but I have some problem to change the efuse value:
"I changed the efuse value to 0x07 (BOD off)"

I' dont know how to edit the boards.txt file and how to install it in the arduino pro mini.

Could you explain the procedure step by step or link me a good complete tutorial ?

Thank you very much