NRF52840 locking up trying to communicate with CO2 Sensor

Other Hardware Sensors
1

I am using a seeed nRF52840 (link)
and trying to communicate with a senseair K33 CO2 sensor

Here is my code that works for about 2 minutes, then seems to halt randomly. It will stop printing to the console until I remove power and plug back in.


#include <Wire.h>
#include "Adafruit_TinyUSB.h"


int co2Addr = 0x68;


void setup() {
  Serial.begin(115200);
  while(!Serial)
  {
    delay(5);
  }
  Serial.println("Program Started");
  Wire.setClock(100000); // Set I2C clock speed to 100 kHz
  Wire.begin();
}


double readCo2() {
  Serial.println("Starting readCo2() function");
  int co2_value = 0;

  // Clear I2C bus
  Wire.beginTransmission(co2Addr);
  byte clearBusResult = Wire.endTransmission();
  Serial.print("Clear bus result: ");
  Serial.println(clearBusResult);
  delay(5);  // Wait a bit before sending the actual command

  Wire.beginTransmission(co2Addr);
  Wire.write(0x22);  // Command to read from RAM
  Wire.write(0x00);  // High byte of number of bytes to read
  Wire.write(0x08);  // Start address (high byte of CO2 value)
  Wire.write(0x2A);  // Checksum for the write sequence
  byte transmissionResult = Wire.endTransmission();
  Serial.print("End transmission result: ");
  Serial.println(transmissionResult);

  delay(20);  // Wait for the sensor to process the command

  Serial.println("Requesting data from sensor");
  Wire.requestFrom(co2Addr, 4);
  byte buffer[4] = {0, 0, 0, 0};

  if (Wire.available() == 4) {
    Serial.println("Reading data from buffer");
    for (int i = 0; i < 4; i++) {
      buffer[i] = Wire.read();
      Serial.print("Buffer[");
      Serial.print(i);
      Serial.print("]: ");
      Serial.println(buffer[i], HEX);
    }

    co2_value = (buffer[1] << 8) | buffer[2];
    Serial.print("CO2 Value: ");
    Serial.println(co2_value);

    byte sum = buffer[0] + buffer[1] + buffer[2];
    Serial.print("Calculated checksum: ");
    Serial.println(sum, HEX);
    Serial.print("Received checksum: ");
    Serial.println(buffer[3], HEX);

    if (sum == buffer[3]) {
      Serial.println("Checksum valid");
      return (double)co2_value;
    } else {
      Serial.println("Checksum invalid");
      return (double)-1;
    }
  } else {
    Serial.println("Insufficient data received");
    return (double)-1;  // Communication failed
  }
}



void loop() {
  unsigned long currentTime = millis();
  Serial.print("Time since start: ");
  Serial.print(currentTime / 1000);  // Convert milliseconds to seconds
  Serial.println(" seconds");
  double co2Value = readCo2();
  if (co2Value >= 0) {
    Serial.print("CO2: ");
    Serial.println(co2Value);
  }
  else {
    Serial.println("Checksum failed / Communication failure");
  }
  delay(2000);
}

I have the 5V rail from the nRF powering the CO2 sensor, and then i2c lines connected as expected on pins 4 and 5.

Any suggestions why it seems to "lock up" ?

Blockquote

2

So, what was the last thing printed? And is that consistent?

3

I see in the documentation that this call returns the number of bytes that were returned. So you might want to check here for the byte being returned has a value of 4 and an error if not 4.

4

No unfortunately not.
I actually just ran a test running this only:

double readCo2() {
  Serial.println("Starting readCo2() function");
  int co2_value = 0;

  // Clear I2C bus
  Wire.beginTransmission(co2Addr);
  byte clearBusResult = Wire.endTransmission();
  Serial.print("Clear bus result: ");
  Serial.println(clearBusResult);
  delay(5);  // Wait a bit before sending the actual command
}

After about 1 minute (not repeatable) it will stop printing to console

5

With all the serial.print calls, you must be able to determine the last message to be displayed! What is it?

6

It ranges. but typically lands on Serial.print("Time since start: "); right before the call to the readCO2() function. But I have seen in land on the Serial.print("Clear bus result: "); as well

7

Which model sensor do you have? Is it 3.3V, to match the processor?

Rather than read one byte and print, I suggest to read all four bytes, then do other things like print.

    for (int i = 0; i < 4; i++) {
      buffer[i] = Wire.read();
      Serial.print("Buffer[");
8

Yes, very strange!
Try moving ALL your locally defined variables to globally defined and see if that changes anything.