Photodiode Values

Other Hardware General Electronics
1

i have a Circuit and code for a photo-diode but i am not getting any Values from it , even if i Flip it around , i do not have any resistor value labeled as i have tried several Values with no luck, Strange thing is that if i disconnect A0 i get Values. any help would be appreciated

PhotoDiode 

// Reading PhotoDiode 
int sensorPin = A0;
int sensorValue = 0;

void setup(void) {
   Serial.begin(9600);
   pinMode(sensorPin, INPUT); 
}
 
void loop(void) {
   sensorValue = analogRead(sensorPin);
   Serial.println(sensorValue);
}

Circuit
Circuit232×118 2.83 KB

2

Reverse the photodiode. Photocurrent flow is in the opposite direction of the diode arrow, and the analog input cannot read negative voltages.

What value of resistor?

3

Since you connected it to GND - you think the photodiode will generate current?

4

If a pin isn't connected to anything then it is floating and will pick up noise from the environment, which is what you are seeing.

1 Like
5

Scratched the old Circuit the New Circuit and it Works fine now .. :slight_smile:

Circuit
Circuit232×118 2.42 KB

6

The current from a photodiode is very small and you generally need a Transimpedance Amplifier.

A phototransistor would be easier to use.

Although, I MIGHT be wrong since the input impedance on the Arduino is very-high and you MIGHT get enough voltage to read/measure.

And of course it depends on if you are reading direct sunlight or the output from a little LED. :wink:

And I assume you know that's in an infrared photodiode.

1 Like
7

Great, but the schematic is drawn with the photodiode in the wrong orientation, and the resistor has no practical effect.

8

What are you going to use it for? If I want a rough indication of light level I use an LDR. I'm just curious about why you chose a photo diode and not a photo transistor or an LDR.

9

Dave , Gaps in labels is what we are using it for , have you off by chance know any good Slot readers for Labels. affordable wise

10

yes i know we are using a LED on the Other Side they are pointing towards each other

11

I don't know anything about them, sorry.

12

Use a phototransistor not a photodiode.
A phototransistor will give you a digital outout (ON/OFF) that you can connect to an Arduino digital pin.

13

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