Pardon my noobness. I'm trying to set up a simple IR LED – Phototransistor pair but am having difficulties. My setup is just as in the following link, except my resistor values are 1K.
http://www.nerdkits.com/videos/theremin_with_ir_distance_sensor/
I'm using an Arduino to read the value of the voltage at the emitter but it does not change no matter what I do. I know I'm using the Arduino correctly because I can change the analog pin around and get expected values. I'm guessing I have some fundamental misunderstanding. Is it perhaps where you place the IR LED in relation to the phototransistor? They are right besides each other and I moved them around a bunch with no change. I will post a picture when I get home.
Also, what does varying the amount of current through the IR LED change? The wavelength is always the same, right?
Another question, this is the datasheet for the phototransistor: http://www.jameco.com/webapp/wcs/stores/servlet/Product_10001_10001_373001_-1
A red LED will work to, since this is somewhat sensitive to red light, right?
Best Answer
Are you using the 1K resistor in series with the IR LED? Because based on the datasheet from that page that won't be enough current to really drive it. That will give you about 3.5mA and you need more like 100 mA. So try using a 100 Ohm resistor there instead.
Another cool trick is if you have a camera phone, old webcam or digital camera a lot of times if you point them at your IR LED you'll be able to see it turn on, on screen. Try it yourself by pointing your remote control at your phone and hitting some buttons. Also that might be a good way to see if your detector is outputting anything too. Point it at your IR detector and hold down the volume button and see if you get anything on the Audrino (or even better a scope if you have one).
The wavelength stays more or less the same, but more current = more light or in your case any light at all.
Red might work but I suspect it might be that your LED isn't on.
Good luck!