💬 Battery Powered Sensors

[TheoL]

@tssk First things that comes to my mind is that you might draw too much power (but no expert) did you measure it?

[canique]

@tssk There is a name for this noise: it is called "coil whine". In German "Spulenfiepen". It stems from the inductor - I wouldn't know any way to get rid of it.
My mainboard or power supply on my PC creates similar noise when the CPU goes in certain doze modes.

[BearWithBeard]

@tssk I heard that people got rid of or at least reduced the coil whine by coating the windings of an audible inductor with non-conductive materials like epoxy resin or even hot glue to reduce the vibrations.

Of course, I woudn't mess with expensive PC hardware, but I guess there's not much to loose with a cheap boost module like this.

[tssk]

Thanks all for the response.

@BearWithBeard I will start googling about such solution.

Do you think using different step up booster might help? Could someone recommend something?

[canique]

I am biased since I run that website but I can recommend https://www.canique.com/boost
I've never heard it making noise.

[tssk]

@canique Thanks for the recommendation if I do not find fix for the model I am using I will consider buying it.

I will try to hot glue the side with the coil as I found on some pages. Any ideas / warnings? :)

[zboblamont]

@tssk Most of these boosters have a grounded backplane, perhaps trying to re-orientate the inductor so the backplane acts a shield to direct RF may be an option to try ?
If the noise in on the power line I've heard of some managing to block it with a VR circuit if the voltage drop is acceptable, but never tried it.

[tssk]

@zboblamont It is not electrical noise but audio noise I can hear. Sorry if I use improper terms.

[zboblamont]

@tssk My misconception.

[skywatch]

@tssk If the item is not going to be too hot then hot melted candle wax dripped over the coils will probably help.

[tssk]

So I used hot glue and it is better. Now I can hear the squeal only when I put my ear directly to the PCB. Thanks for the tips.

@TheoL I have no idea how to measure that.

I noticed that when the radio is transmitting the LED on the Arduino Pro Mini (not the power one) starts blinking very tiny. I still plan to remove the power LED and voltage regulator from the Arduino.

[mfalkvidd]

@tssk the led blinks because it is connected to the same pin as the SCK pin used by the nrf24.

[tssk]

@mfalkvidd You are right :) I did not know that.

SPI: 10 (SS), 11 (MOSI), 12 (MISO), 13 (SCK). These pins support SPI communication, which, although provided by the underlying hardware, is not currently included in the Arduino language.
LED: 13. There is a built-in LED connected to digital pin 13. When the pin is HIGH value, the LED is on, when the pin is LOW, it's off.

https://www.arduino.cc/en/pmwiki.php?n=Main/ArduinoBoardProMini

Should I remove the LED to save power? Or it is marginal?

[mfalkvidd]

@tssk it is marginal

[tssk]

@mfalkvidd Thanks.

[tssk]

Hello

I would like to ask for help with passive battery powered node I created with following components:

• Arduino pro mini 8MHz - voltage regulator and power LED removed
• SX1276 based 868MHz LoRa radio
• BME680 sensor
• DC-DC 3.3V step-up booster

I created a battery measuring circuit according to scheme on this page ( https://www.mysensors.org/build/battery ).

The problem is the two fresh new AA batteries lasted less than 14 days and stopped when the circuit measured 36%.

2x1.5V AA Aerocell following start and end values:

09.02.2021 16:45 102% (start) : 1.610V and 1.610V
22.02.2021 04:15 36% (end) : 1.001V and -0.150V

The node code is sleeping for 6 minutes between each sensing and sending data.

sleep(180000);

14 days seems very short to me. Is that normal? Is there something I can to make it last longer?

Thanks

[mfalkvidd]

@tssk could you post your sketch? Some things that could draw power:

• bme not turned off properly when sleeping the node
• lora transmits can take a long time, depending on which settings are used

Which booster are you using? A good booster will use almost no power when the node is sleeping. A bad booster will consume almost as much as if the node was not sleeping, so the performance of the booster will make a huge difference.

[skywatch]

@tssk Sending 240 messages a day is quite a lot for a battery node. I think you will need higher capacity batteries with that frequency of sending (is it really essential to send that often I wonder?).

Anyway, I am also testing battery nodes and as far as I can see the lora and bme are likely taking a lot of power. They must be 'put to sleep' as much as possible. AFAIK lora is an abbreviation of 'long range' and therefore means 'more power'. Can you test the current drawn by just the radio in sleep and transmitting?

Also, bootloader - I highly recommend using the minicore bootloader with internal 8MHz, bod as you wish (I ususally disable) and try again. My sleeping nodes use less than 5uA in sleep and I am trying to get that even lower this week.

Also check the value of pull-upresistors on the boards, they can be on the low side and perhaps better with higher value external ones (something I hope to test tomorrow as it happens).

Also temperature and humidity will have an effect. I put one test node on a colder NE facing window which has slept all the time except a twice daily battery check and send value only if changed. It is the only node to have changed from 100% to 99% in a week, so the colder window is clearly having an effect on the battery life in this situation.

As @mfalkvidd implied I would get rid of the stepup booster if at all possible, they are not so efficient and can produce a lot of noise on the power line. Can you go to 3xAA batteries? What about an 18650 li-on or two in parallel?

Finally check solder joints. A dry joint or cold joint may look OK but measure them with a meter just to make sure.

[tssk]

@mfalkvidd

• I did not know that I need to turn BME off ů how to do that?

• Only thing I found is that Arduino has deepSleep() - but I am not sure if I can use it.

• I am using the default Bw125Cr45Sf128 but thinking about testing Bw125Cr48Sf4096 to achieve greater range.

• Booster is the whining one - https://www.laskarduino.cz/step-up-boost-menic-s-me2108-33v-480ma/

• Is there a way I can measure power draw with multimeter?

// Enable debug prints
//#define MY_DEBUG

// Enable passive mode
#define MY_PASSIVE_NODE

// Passive mode requires static node ID
#define MY_NODE_ID 100

// Enable and select radio type attached
//#define MY_RADIO_RF24
//#define MY_RADIO_NRF5_ESB
//#define MY_RADIO_RFM69
#define MY_RADIO_RFM95

//#define MY_DEBUG_VERBOSE_RFM95
#define MY_RFM95_FREQUENCY (RFM95_868MHZ)
//#define MY_RFM95_MODEM_CONFIGRUATION RFM95_BW31_25CR48SF512
#define MY_RFM95_CS_PIN 8
#define MY_RFM95_IRQ_PIN 2

#include <MySensors.h>
#include <Wire.h>
#include <SPI.h>
#include <Adafruit_Sensor.h>
#include "Adafruit_BME680.h"

#define BME_SCK 13
#define BME_MISO 12
#define BME_MOSI 11
#define BME_CS 10

//#define SEALEVELPRESSURE_HPA (1013.25)

// Initialize general message
MyMessage msgTemp( 1, V_TEMP );
MyMessage msgHumi( 2, V_HUM );
MyMessage msgAirq( 3, V_LEVEL );

//Adafruit_BME680 bme; // I2C
Adafruit_BME680 bme(BME_CS); // hardware SPI
//Adafruit_BME680 bme(BME_CS, BME_MOSI, BME_MISO,  BME_SCK);

void setup()
{
  analogReference(INTERNAL);

  if (!bme.begin()) {
    Serial.println( "ERR: BME680 not found" );
    while (1);
  }
  // Set up oversampling and filter initialization
  bme.setTemperatureOversampling(BME680_OS_8X);
  //bme.setPressureOversampling(BME680_OS_4X);
  bme.setHumidityOversampling(BME680_OS_2X);
  bme.setIIRFilterSize(BME680_FILTER_SIZE_3);
  bme.setGasHeater(320, 150); // 320*C for 150 ms

  delay(2000);
  
}

void presentation()
{
	// Send the sketch version information to the gateway and controller
	sendSketchInfo("Room sensor", "4.0");

	// Register all sensors to gw (they will be created as child devices)
  wait(100);
	present( 1, S_TEMP );
  wait(100);
  present( 2, S_HUM );
  wait(100);
  present( 3, S_AIR_QUALITY );

}

void loop()
{

  int batt = analogRead( A3 );
  // 1M, 470K divider across battery and using internal ADC ref of 1.1V
  // Sense point is bypassed with 0.1 uF cap to reduce noise at that point
  // ((1e6+470e3)/470e3)*1.1 = Vmax = 3.44 Volts
  // 3.44/1023 = Volts per bit = 0.003363075
  int battP = batt / 10;
  #ifdef MY_DEBUG
      float battV  = batt * 0.003363075;
      Serial.print( "Battery Voltage: " );
      Serial.print( battV );
      Serial.println(" V");
      Serial.print( "Battery percent: " );
      Serial.print( battP );
      Serial.println(" %");
  #endif
  wait(100);
  sendBatteryLevel( battP );
  

  if (! bme.performReading()) {
    Serial.println( "ERR: BME680 reading failed" );
    return;
  }
  
  float temp = bme.temperature;
  #ifdef MY_DEBUG
    Serial.print( "DBG: Temperature = " );
    Serial.print( temp );
    Serial.println( " C" );
  #endif
  wait(100);
  send(msgTemp.set( temp, 2 ));
  
  /*
  float pres = bme.pressure/100.00;
  #ifdef MY_DEBUG
    Serial.print( "DBG: Pressure = " );
    Serial.print( pres );
    Serial.println( " hPa" );
  #endif
  wait(100);
  send(msgPres.set(pres,2));
  */
  
  float humi = bme.humidity;
  #ifdef MY_DEBUG
    Serial.print( "DBG: Humidity = " );
    Serial.print( humi );
    Serial.println( " %" );
  #endif
  wait(100);
  send(msgHumi.set( humi, 2 ));
  
  /*
  float alti = bme.readAltitude(SEALEVELPRESSURE_HPA);
  #ifdef MY_DEBUG
    Serial.print( "DBG: Approx. Altitude = " );
    Serial.print( alti );
    Serial.println( " m" );
  #endif
  wait(100);
  send(msgPosi.set(alti,2));
  */

  float airq = bme.gas_resistance / 1000.0;
  #ifdef MY_DEBUG
    Serial.print("DBG: Gas Resistance = ");
    Serial.print( gas );
    Serial.println(" KOhms");
  #endif
  wait(100);
  send(msgAirq.set( airq, 2 ));
  
  
  sleep(10000);
	//sleep(180000);
}

[tssk]

@skywatch

• This is room sensor and I would like to react to changes in temperature and airquality - I was thinking that I could prolong the interval up to 12min. What do you think is optimal measurements rate for room thermostat?

• Is it possible / necessary to put the radio module to sleep? How to do that?

• So far I did not mess with the Arduino bootloader but I would like to :) Any link that I could read about it? And specifically about the minicore you mention?

• I do not understand what you mean by the pull-up resistors?

• I have my node in the middle of the room around 20-24C that sould not be the problem. Actually it is it main purpose to provide data for optimal room temperature.

• I included step up boosted based on recommendation on the https://www.mysensors.org/build/battery page. I thought it should use the batteries most efficiently. I think I could go with 3 AA batteries. Will I need to regulate the voltage or can I power the radio and bme modules directly?