Arduino Nano 33 BLE power consumption optimization

Projects Programming
1

Greetings everyone!

I am working on building a sensor using Arduino Nano 33 BLE that will measure temperature using two thermistors and angle changes. The measured values will be transmitted over Bluetooth to a smartphone every minute. I have written the code for temperature and angle measurements, as well as remote data transfer. However, I need this sensor to operate for 10 to 21 days on a 3.7v 250mAH battery. To achieve this, I planned to use the Arduino low-power library.

Unfortunately, I have not been able to find a library that is compatible with this Arduino board, nor have I found an example of how to put the board into sleep mode and then measure values every minute. I am aware of the option to power the board directly from a 3.3v source by cutting the 3.3V pads on the back of the board, disabling the power indication diode and turning off the sensors/the I2C pull-up resistors.

I would appreciate any suggestions or solutions to this problem. The full code of the sketch is below:

`#include <ArduinoBLE.h>
#include <Arduino_LSM9DS1.h>
//These  values are in the datasheet
#define RT0 100000   // Ω
#define B 4600      //  K
//--------------------------------------
#define VCC 3.3    //Supply  voltage
#define R 100000  //R=100KΩ
//Variables`your text`
float RT, VR, ln, TX0, TX1,  T0, VRT1, VRT0;
unsigned long last_time;
float x, y, z,angleX,angleY;
// Define the BLE service and characteristic
BLEService greetingService("180C");
BLEStringCharacteristic greetingCharacteristic("2A56", BLERead | BLENotify, 30);
void setup() {
  // Initialize BLE
BLE.begin();

  // Set up the service and characteristic
greetingCharacteristic.setValue("Hi");
greetingService.addCharacteristic(greetingCharacteristic);
BLE.addService(greetingService);

  // Start advertising the service
BLE.advertise();
Serial.begin(9600);
  T0 = 25 + 273.15;  
if (!IMU.begin()) {
Serial.println("Failed to initialize IMU!");
while (1);
}
Serial.print("Accelerometer sample rate = ");
Serial.print(IMU.accelerationSampleRate());
Serial.println("Hz");
   // Set the initial rotation angles to 0
  angleX = 0;
  angleY = 0;
}
void loop() {
if (millis()-60000>last_time){
  last_time=millis();
  VRT0 = analogRead(A0);              //Acquisition analog value of VRT
Serial.println(analogRead(A0));
  VRT0  = (3.30 / 1023.00) * VRT0;      //Conversion to voltage
  VR = VCC - VRT0;
  RT = VRT0 / (VR / R);               //Resistance of RT
  ln = log(RT / RT0);
  TX0 = (1 / ((ln / B) + (1 / T0))); //Temperature from thermistor
  TX0 =  TX0 - 273.15;                 //Conversion to Celsius
Serial.print("Temperature1:");
Serial.print("\ ");
Serial.print(TX0);
Serial.println("\ C");
  VRT1 = analogRead(A1);              //Acquisition analog value of VRT
Serial.println(analogRead(A1));
  VRT1  = (3.30 / 1023.00) * VRT1;      //Conversion to voltage
  VR = VCC - VRT1;
  RT = VRT1 / (VR / R);               //Resistance of RT
  ln = log(RT / RT0);
  TX1 = (1 / ((ln / B) + (1 / T0))); //Temperature from thermistor
  TX1 =  TX1 - 273.15;                 //Conversion to Celsius
Serial.print("Temperature2:");
Serial.print("\ ");
Serial.print(TX1);
Serial.println("\ C");
IMU.readAcceleration(x, y, z);
Serial.print("x=");
Serial.print(x);
Serial.print("y=");
Serial.print(y);
Serial.print("z=");
Serial.print(z);
    // Calculate the rotation angles using the atan2 function
    angleX = atan2(y, z) * 180 / PI;
    angleY = atan2(x, sqrt(y * y + z * z)) * 180 / PI;
    // Map the rotation angles to the range [0, 360]
    angleX = fmod(angleX + 360, 360);
    angleY = fmod(angleY + 360, 360);

  // Print the rotation angles
Serial.print("Rotation X: ");
Serial.print(angleX);
Serial.print(" degrees, Rotation Y: ");
Serial.print(angleY);
Serial.println(" degrees");

  BLEDevice central = BLE.central();
if (central) {
    // Send the value of x to the connected device
    String message = String(TX0)+"/"+String(TX1)+"/"+String(angleX)+"/"+String(angleY);
greetingCharacteristic.writeValue(message);
}
}
}`
2

Use the "LowPower.h" library:
#include <LowPower.h>

Put that at the beginning and then put the following command in the place of whatever command you used to delay the 1 minute interval:
LowPower.idle(SLEEP_60S, [whatever you want off]_OFF)

How it works:
The "LowPower" library allows your arduino to reduce its power consumption. Since you want a 1 minute interval, the "SLEEP_60S" puts your arduino to sleep for 60 seconds. You place whatever you want off in the "[whatever you want off]" to further reduce power consumption. Tell me if there you experience any problems with this solution.

3

The simplest option, that also saves the most energy, is to use a power timer. You can have the entire system powered up every 10 minutes, every hour, etc. then power down again.

Example: Overview | Adafruit TPL5110 Power Timer Breakout | Adafruit Learning System

I need this sensor to operate for 10 to 21 days on a 3.7v 250mAH battery.

Assuming 10 days, that means the average current draw has to be less than 250 mAh/(240 h) or less than about 1 mA. To take into account battery aging and seller exaggeration, reduce that average to 0.5 mA.

4

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