Ultrasonic unit reads erroneous distance

aafortinet

Hello, I have a M5 CoreInk onto which I have plugged a Ultrasonic sensor. I am getting a buggy distance read all the time.

[-] bad distance: 4294967.500000
[-] bad distance: 4294967.500000
[-] bad distance: 4294967.500000

My code is very much taken from this example.

This is how I initialized Wire. I am not sure about this Wire.begin(21,22). It is taken from this code, but this other code uses other values...

void setup() {

    M5.begin(); //Init CoreInk.  
    if( !M5.M5Ink.isInit()) //Init CoreInk screen.
    {
        Serial.printf("[-] M5Ink init failed");  
        while (1) delay(100);
    }

    Wire.begin(21,22);
    Serial.printf("[+] Wire begin done\n");
    
    M5.M5Ink.clear();   //Clear screen.  
    ...

And this is how I read distance. This looks good to me...

#define M5_I2C_ADDR_ULTRASONIC 0x57
float readDistance() {
  uint32_t data;
  Wire.beginTransmission(M5_I2C_ADDR_ULTRASONIC); 
  Wire.write(0x01);
  Wire.endTransmission(); 
  delay(120);
  Wire.requestFrom(M5_I2C_ADDR_ULTRASONIC,3); 
  data  = Wire.read();data <<= 8;
  data |= Wire.read();data <<= 8;
  data |= Wire.read();
  return float(data) / 1000; // distance in mm
}

and then the loop - can't see anything wrong either...

void loop() {
  static float newvalue = 0;
  newvalue = readDistance();
  if ((newvalue < 1500) && (newvalue > 0)) {
    Serial.printf("Distance: ",newvalue);
  } else {
    Serial.printf("[-] bad distance: %f\n",newvalue);
  
  }
  delay(100);

}

Can you help me spot the error? Or is my sensor faulty? or is something different with CoreInk?

Thanks

aafortinet

I fixed my problem using

Wire.begin(32,33);

The distance now makes sense. I don't know what these values are for, though...

Also, my distance is not precise. I'll investigate and post again if the problem persists.

aafortinet

The distances I get are really strange:

The values are well below or well above the expected ones. For example, for a distance of ~95cm the sensor answers 4.5cm. For a distance of ~110cm, 4.9cm. For ~35cm, 3.7cm etc.
The values change for the same distance. So different measures of ~200cm gives 13.7cm or 79.6cm the next time...

The command Wire.begin(32,33) seems correct as I realize those are the ports for the sensor on the CoreInk.

So, what am I doing wrong?