IR led sensing IR led Reflections.

I am playing around with some IR leds, 940nm, and photo diodes. The problem i run into is the Photodiode will not pick up the reflections, it will only detect when it has a direct beam from the IR led. Here is my code,

include "Tlc5940.h"

int grid0 = A0; int grid0Value = 0; int readPin; int triggerPin;

void setup() { /* Call Tlc.init() to setup the tlc. You can optionally pass an initial PWM value (0 - 4095) for all channels.*/ Tlc.init();

Serial.begin(9600); }

void loop() {

grid0Value = analogRead(grid0);

Serial.println("GridValue0 ="); Serial.println(grid0Value);

int grid0PWM = 200 * grid0Value; Tlc.clear();

Tlc.set(1, grid0PWM); Tlc.set(2, grid0PWM); Tlc.set(3, grid0PWM); Tlc.set(4, grid0PWM); Tlc.set(5, grid0PWM); Tlc.set(6, grid0PWM); Tlc.update();


The IR diode is hooked up like this, 5v - 73ohm resistor- ir diode- ground. The IR reciever is hooked up like this. Vcc - 100ohm - reciever - 5k ohm- ground . -- Signal is being pulled from in between 5k and photodiode. the sensor section mimics Octolively from Evil Mad Science, but the only way they work is if the diodes are pointing each other.

Any pointers?

Perhaps you need to amplify the output from the diode. I recall that my TV could be controlled by pointing the remote in any direction in the room.


Why the 100R resistor, it makes no sense. Make the 5K into a 100K to increase the sensitivity. However even so the reflective range you are going to get is in the order of a few mm at most without an amplifier.

Thanks for the info Mike, as for why i was using the resistors, Octolively used them, thats what i set my base sense circuit. I just put the circuit on a O-scope and it works to a degree if I use a cd on top of it.

Ill try changing the 5k to 100k and see whats happens.

BTW, the Diodes i am using are lte-5208a and ltr-3208e. both 940nm and the emmiter is 40degrees.

towards in is schematic.

Thanks mike, that seem to do the trick, along with a good If, else statement. Has a range of about 3-4 inches :)

Can you please post your schematic, as I'm planning on using reflected IR in one of my projects.

Henry_Best: Can you please post your schematic, as I'm planning on using reflected IR in one of my projects.

It is in the PDF given in that last post.

Yeah, go to last page of the PDF, also go to there site, its open source so they give the AVR firmware too.


Just for the record, the amp configuration often used is a “transimpedance op-amp circuit.” That would greatly increase range, but, also make more prone to noise, such as
room light.

project is comming together. Initial test are working, Full scale will be 8 TLC5940s and some ADCs via i2c. 24 grids, 120ish leds.. :)