Lux sensor (BH1750) sending battery level (V)

[FrankVK]

Hi,

I really enjoy using MySensors!

Got a small general question though: I'm using a BH1750 light sensor, powered by a 3V battery and I'd like to keep an eye on the battery status.

I have added a line to the existing BH1750 scetch:

#define CHILD_ID_VCC = 1
MyMessage msgVcc(CHILD_ID_VCC, V_VOLTAGE);
.. 
void Presentation() {
  sendSketchInfo("Light Lux Sensor", "1.1");
  present(CHILD_ID_LIGHT, S_LIGHT_LEVEL);
  present(CHILD_ID_VCC, S_MULTIMETER);
}

Loop() {
uint16_t lux = lightSensor.readLightLevel();
float Vcc = ReadVcc();

send(msgLux.set(Lux));
send(msgVcc.set(Vcc));
}

Domoticz recieves the data now, but the Voltage is reading 2968V because readVcc delivers mV
If I change the code to:

float Vcc = readVcc()/1000;

I get an error message "call of overloaded 'set(float&)'is ambiguous"
How can I send decimal values to the Domoticz controller from MySensors?

Regards, Frank

[zboblamont]

@frankvk No programming skills, but is it correct trying to calculate in a procedure call rather than insert an intermediate step?
If the ReadVcc() procedure call returns millivolts, suggest preceding the "float Vcc = ReadVcc();" with "int Voltage= ReadVcc();" and change the "float Vcc = ReadVcc();" to "float Vcc = Voltage/1000;", it should then do as you want.

[FrankVK]

Hi Zboblamont,

Thanks for your response, but the error occurs in the line, obviously because Vcc is of the type 'float'

send(msgVcc.set(Vcc));

[zboblamont]

@frankvk I'm no expert on this, but do know all my nodes send battery as a float for the last 2 years, excerpt as follows:

// Call for battery reading, send in every 12th RTC call?
   if(halfday==12){
   digitalWrite(BatteryOn, HIGH);
   voltread = analogRead(BatteryIn);
   float voltage = (7.272 * voltread) / 1024;
   sleep(5);
   digitalWrite(BatteryOn, LOW);
   send(msg3.set(voltage,2));
   sleep(50);
   voltread=0;
   sleep(50);
   halfday=0;//Reset for 12 hourly cycle
}
   halfday++;//Increment hourly cycle

That is based on the internal value defined without any complications, but note that the message is sent to 2 decimal places, whether that truncation is essential for the MySensors environment I do not know, it was all I required.

[electrik]

Is there a typo in your message or in your code?
First you used ReadVcc(), then readVcc()

[mfalkvidd]

@frankvk could you post the entire sketch, including where readVcc comes from? Seeing the code will make it much easier to help you.

[bgunnarb]

The line

float Vcc = readVcc()/1000;

should be:

float Vcc = readVcc()/1000.;

to start with. Note the decimal point! If read Vcc() returns a float, you cannot divide by an integer.

[kimot]

@bgunnarb
But readVcc returns long

long readVcc() {
  long result;
  // Read 1.1V reference against AVcc
  ADMUX = _BV(REFS0) | _BV(MUX3) | _BV(MUX2) | _BV(MUX1);
  delay(2); // Wait for Vref to settle
  ADCSRA |= _BV(ADSC); // Convert
  while (bit_is_set(ADCSRA,ADSC));
  result = ADCL;
  result |= ADCH<<8;
  result = 1126400L / result; // Back-calculate AVcc in mV
  return result;
}```

[mfalkvidd]

A float can be divided by an integer. The result will be a float.

A long can be divided by an integer or a float. The result will differ though.
2968/1000 will give the integer 2
2968/1000.0 will give the float 2.968

See "Integer and floating point division" at https://www.learncpp.com/cpp-tutorial/32-arithmetic-operators/

[zboblamont]

@mfalkvidd @bgunnarb Something new learned from that, hadn't realised a procedure call could be mathematically manipulated like that, nor the subtle differences in the outputs...

[FrankVK]

Actually, I needed to change 2 things: first one was dividing by 1000.0 rather than 1000 and the other one was calling send(msgVcc.set(Vcc, 2)); rather than send(msgVcc.set(Vcc)); Now the log reads 2.95V.

Thanks Mikael (@mfalkvidd) & everyone! Happy coding!

[bgunnarb]

@mfalkvidd
Yep, this is a great way of introducing errors that will be nearly impossible to find!