IR Beam Breaker

[meecree]

I have an IR LED and a IR photodiode.

I know how to connect these components to make a logic high when the beam is broken....or so I thought.

The problem is I'm getting very little sensitivity from the receiver, I know the LED and receiver are working but nothing is giving me enough voltage output to get a logic high unless the transmitter and receiver are touching. I've tried everything I can think of, using resistors to make a potential divider an so on....

My LED is connected to 5v, 100 ohms resistor and ground. The receiver is in reverse bias and makes a potential divider chain (many valued tried), output taken from the middle of the divider chain.

Is it possible my components are miss matched? The highest sensitivity of the reciever is 900nm, and the LED emmits 920nm, seeming not enough different to kill the sensitivity so badly according to the data sheets.

I go on youtube and see people getting these to work in seconds using no extra components and the same resistors I am using, I have a degree in electronics and can't do it!!

Please someone let me know what else could be going wrong??

Help would be greatly appreciated.

[pebe]

Your figure of 900nm is the wavelength of the light being used - not the sensitivity. For maximum sensitivity you should ensure the LED emitter and photo sensor both use the same wavelength.

You are not likely to get logic level outputs from the sensor without some amplification. See here for many ways to do it.

http://www.imagineeringezine.com/files/air-bk2.html

[sunilsuta]

Pebe,I've similar kind of problem.in my case I've matched tx and rx ir led pair.but I am finding it difficult in operating at 3 feet range.how can I fix this problem?

[pebe]

Cannot tell without circuits. Can you supply circuits of Tx and Rx?