coin-cell (CR2032) powered temperature sensor

[Moebius Lutching]

Just found this post https://www.hackster.io/Talk2/temp-and-humidity-sensor-with-a-cr2032-for-over-1-year-580114 showing some details about using a CR2032 to power a sensor node. By my calculations, if the author removed the LED at all the solution would last for over 2 years!

[carleki]

@fleinze said:

@carmelo42

The no-resistor-library can be found here:
https://wp.josh.com/2014/06/23/no-external-pull-up-needed-for-ds18b20-temp-sensor/

The resistors (there are two but the other one is barely visible) are for voltage-measurement. In a later version I got rid of them using this resistor-less method of measurement:
http://provideyourown.com/2012/secret-arduino-voltmeter-measure-battery-voltage/

great :)

Did you change the bootloader ? Which one did you use ?

[Nca78]

Hello,

there are a few improvements you can do to make your CR2032 nodes last longer:

• add a capacitor of 100-200µF in parallel with your battery. Ceramic is better, but I have no problem with nodes using electrolytic capacitors. This will help when there is a peak power consumption from the radio. If you do not put one, voltage will drop quickly and that's probably what is triggering reboot loop on one of your nodes: maybe radio is less efficient and needs to resend more messages. Or maybe your BOD is not updated so it resets when voltage drops at 2.7V...
• in your code, add a sleep command between message sending to give time for your cell to rest, and for the capacitor to recharge. Do it also at the beginning of presentation method and between each message sending in presentation.
• use a better sensor that can accept a lower voltage, they are more expensive that DS18 but they can work down to 2V and use much less current: BMP180/280 if you want to measure only temperature (with barometer as extra), SI7021 for temp/hum, BME280 for temp/hum more expensive but better.
• do not use voltage divider at all, you don't need one as you can just get Vcc from the A0 pin (with it I have some change of voltage related to temperature but not as wild as you seem to get. Maybe it's related to the DS18 measurement also ?)

With these changes and a si7021 breakout board from which I removed the voltage regulator (it's not consuming much, but without it is even better), I can send every minute, flash a led and I hardly see any drop in voltage after a few weeks of running.

[fleinze]

@Nca78 said:

add a capacitor of 100-200µF

I will try this, thanks! Currently I use the 10uF capacitor which is on the arduino pro minis on the raw pin side.

in your code, add a sleep command between message sending

How long do you sleep? In normal operation there is only one send command per loop, I only send battery level once every hour. I try to read vcc after sending the temperature so the battery is under some load when measuring.

use a better sensor that can accept a lower voltage

I already built one with a Si7021 sensor. But I ran out of CR2032 so I powered it using two AA cells. I should solder it back to coin cell now I got some.

you can just get Vcc from the A0 pin

I don't know this method do you have a link or can you explain it?

[fleinze]

@carmelo42 sorry I somehow missed your post. I use the standard-bootloader as I did not get Optiboot to run on the 3.3V/8MHz pro minis. I set the extended fuse to 0x07 (BOD disabled) by editing boards.txt.

[carleki]

@fleinze said:

@carmelo42 sorry I somehow missed your post. I use the standard-bootloader as I did not get Optiboot to run on the 3.3V/8MHz pro minis. I set the extended fuse to 0x07 (BOD disabled) by editing boards.txt.
thanks !

is is a bit confusing for me :

• we can burn the bootloader from the Arduino IDE : are the fuses written at this moment ?
• we can upload a sketch with the arduino IDE : are the fuses written at this moment ?
• with my researches, I found that for disabling BOD was possible with 0xFF value for efuse ?

I have some lifetime issues with my CR2032 sensor .. and I suspect the fuses are not correctly set ...

If you can light up my mind it will be perfect :)

[fleinze]

@carmelo42 The fuses only are written when you burn the bootloader, not when uploading the sketch. The Arduino IDE takes the fuse bytes from the boards.txt files.
It would also be possible to just set the fuse bytes by using the avrdude-program from a command line, but you will still need to use a programmer.
The extended-fuse setting 0xFF is the same as 0x07 as only the last 3 bits of this bytes are used. Both values will give you BOD disabled.

[fleinze]

I just added an 100uF capacitor to one of my sensors and put an old battery in. Let's see how much more life I can get out of this battery now.

[carleki]

@fleinze
Hi, do you think it's possible to connect de Dallas sensor to pin 7, 8 and 9 of the arduino ?

Like this :

#define ONE_WIRE_BUS 8 // Pin where dallase sensor is connected
#define ONE_WIRE_GND 9
#define ONE_WIRE_VCC 7

I have tried, and the temperature is always 85°C ...

[Nca78]

Hello @carmelo42, pin 9 is supposed to be connected to the NRF24 (CE / Chip Enable) so it cannot work as ground for the sensor as it will be high (and so = to Vcc) most if not all of the time.

[flopp]

@fleinze said:

I just added an 100uF capacitor to one of my sensors and put an old battery in. Let's see how much more life I can get out of this battery now.

Very interest work.
Is it still working?

[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
}```