Go Down

Topic: IR sensor help (Read 2162 times) previous topic - next topic

njs707

K tried that ...

I used a 10k ohm resistor to start, then switched to two 47k ohm resistors in series for 94 k ohms, and always was 1023 reading with slight variations to 1022 and 1021 randomly.  I pressed my tv remote and got no reaction.  Here is how I have it set up...

+ 5v _____ 94 ohm ______ cathode ________ A5
anode_______ground                                                         I believe this is exactly what you mean.

Just using this simple code...



int Receiver =0;


void setup()

{
  Serial.begin(9600);
}
void loop()
{
  int Receiver = analogRead(A5);
  Serial.println(Receiver);
}

TomS

What do you mean by "cathode - A5 - anode" ?!?

You have to measure between the photodiode and the resistor (identified by "Vout" in the paper I linked).

And why don't you try the simplest possible setup (i.e. no reverse voltage) if you are having troubles?
You can always change it later if you do need the reverse voltage.

njs707

The 2 are separate..

+ 5v _____ 94 ohm ______ cathode ________ A5  is separate
This is everything attached to the cathode

only thing attached to the anode of the photodiode is ground.  I tried reverse and it seems to be working better though.  I am also getting other photodiodes ( daylight filtering ) from mouser today. 

Hope those help too.

Ill be back with more questions very very soon.

Grumpy_Mike

#18
Jun 09, 2011, 05:11 pm Last Edit: Jun 09, 2011, 05:15 pm by Grumpy_Mike Reason: 1
Quote
anode_______ground                                                         I believe this is exactly what you mean.


No that is not what I said please re read what I put.
Quote
And why don't you try the simplest possible setup (i.e. no reverse voltage) if you are having troubles?
You can always change it later if you do need the reverse voltage.

No if there is only a reverse diode across the analogue input then the input impedance is too high for the sample and hold on the input. You need an impedance of about 10k to prevent any apparent cross coupling in the multiplexer

TomS

I think you misunderstood me Mike, by simplest possible setup I was referring again to driving the photodiode in short circuit mode (i.e. cathode - resistor - anode) and reading the voltage across the resistor.

Grumpy_Mike

That is not a very good mode. This is because any charge carriers generated in the depletion layer are not necessarily swept out of the layer into the rest of the circuit. Where as applying a bias provides an electric field to get those charge carriers flowing.

TomS

You are right, that is not the best mode to get most accurate readings, but it is by far the most easy to set up and you can hardly connect anything wrong.
So to get things going and get an analogRead from the photodiode up and running it might be worth a try.

Go Up