"Flame sensor" connection

Hello all,
I'm new to Arduino and inexperienced in electronics.

I want to connect a flame sensor to an analog pin of the UNO and just measure the values in the 0-1023 range. I am using a 10K resistor. I don't know the sensor's exact model, but it looks similar to the one here:

I have a couple of questions:

  1. The instructions provided to me illustrate the same diagram as the one shown in the site above. Shouldn't the sensor instead be placed upside down (the "anode" connected to Vcc and the "cathode" to GND/analog input via a resistor as shown eg here: How the Phototransistor Circuit Works | LEARN.PARALLAX.COM )?
  2. When my analog pin is unconnected it gives a floating value of around 330. When I connect it to my flame sensor circuit it's values are fluctuating between 250 and 450 but with no apparent reason. Neither light nor a source of flame changes it in a definite way. This happens even if I connect the sensor upside down.

I suspect that my sensor is damaged.

Does anybody have an idea of what's may be going on?
Thank you

1 )
Both schematics are correct.
A phototransistor is used that way.
But a IR photodiode is used in reverse (blocking) to sense IR waves.
I think that is called "reverse bias".

2 )
There can be so many things, the sensor might still work.
Do you use a breadboard ? those can have bad contact.
Can you try another analog input ?
Perhaps you don't have the flame sensor, but perhaps something else like a IR led. Or your sketch might be wrong.
It is hard to say what to do without knowing the type of sensor.

Thanx a lot, that gave me something to look into :slight_smile:
I use a breadboard and have tried different holes and different analog inputs, too, but the results are the same: fluctuating analog readings that don't seem to be related to light (in fact they fluctuate like a "wave").
In the meantime I would welcome any other ideas.

As a first check of the Arduino analog input, replace the flame sensor with another 10K resistor. The analog input should read about 512 and be very steady. If not, you have a problem. Are all the grounds connected together?

The "flame sensor" is just an IR photodiode and they can be damaged by static electricity. If you have a multimeter, try measuring the resistance of the photodiode in both directions. It should be low in one direction and very high (but depending on local IR sources) in the other. If it tests as an open circuit, it has been destroyed.

Had forgotten to supply and ground one of the four banks of my breadboard. Silly mistake but a lot learned. It's working now. It is a forward bias sensor.

Thank you all.