emonTH reading external analog sensor (TCRT5000), signal on unexpected pin

@bvrslypp wrote:

I am working with the TCRT5000 sensor and an emonTH 1.5 to measure my gas meter (it has a small mirror on the last digit reel, so trying to detect that).

In my first attempt, I tried connecting the sensor to screw terminals 2,3 and 4 (digital input) as done with the optical pulse sensor sold in the shop. This works, but is extremely tricky to get good results as you have to find the “sweet spot” of the sensor, i.e. placing it at the right position on the meter to get get a digital positive reading when the mirror passes by, and a negative reading if the mirror is not in sight.

Therefore, I decided to try to hook the sensor to an analog input, so that I can calibrate it in software. I connected the signal wire to screw terminal 5. According to the wiki page, this should be ADC5 (dig 18), so I tried reading from A5, but got no signal.

Now my confusion starts, as I used the following sketch to see whats going on. I read all inputs:

void setup(){

  pinMode(A3, INPUT_PULLUP); //Experiment, setting it as input
  pinMode(A5, INPUT_PULLUP); 

   
  Serial.begin(9600);

}

void loop(){
  
  printPinAndAnalogRead(A1);
  printPinAndAnalogRead(A2);
  printPinAndAnalogRead(A3);
  printPinAndAnalogRead(A4);
  printPinAndAnalogRead(A5);

  Serial.println();
 
  delay(100);

  
}

void printPinAndAnalogRead(int inputPin) {
    
  int value = analogRead(inputPin);        
  Serial.print(inputPin);
  Serial.print("=");
  Serial.print(value);
  Serial.print("  ");
  
}

Using this code, I get a very clear signal on input A3, i.e. pin 17. However, this does not correspond with the documentation and schematic (which suggest ADC5 / pin 18) and sketch emonTH_DHT22_DS18B20_RFM69CW_Pulse.ino (which suggests pin 18).

Can someone explain this? Would reading from this analog input work if I modify the original sketch by removing all temperature sensor reading code?

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