IR LED for hand detection

Hi all,

I want to create an LED coffee table like this http://www.geeky-gadgets.com/wp-content/uploads/2009/06/rgb-led-coffee-table.jpg. The table itself is no problem and I am already driving a load of addressable RGB LED's for the display.

The bit I'm not sure about is using IR receivers/transmitters for the hand detection (as someone touches the table.)

I have brought some receiver/transmitter LED's on ebay, however I think I might have brought the wrong receivers as they are just 2 pin. If I wire them up and check the voltage i can see a very slight change when my hand goes over it (to bounce the transmitter back to the receiver) however i think there is so much IR coming from home lighting and natural light that its going to be hard to really detect things.

Also, i intend to use a shift register so that I can read 8 at a time serially, so really need a high/low value instead of a gradual voltage.

Any pointers in the right direction would be great.

You’ll have to amplify the signal of the IR receiver diode. Did you try a straight light barrier, instead of reflection?

Ambient light can be filtered out by pulsing the sender diode, and looking for similar pulses on the receiver side.

TheGrovesY: I have brought some receiver/transmitter LED's on ebay, however I think I might have brought the wrong receivers as they are just 2 pin.

Any link to those leds? Just to better understand...

Thanks for the replies.

@docdoc - Sorry i can't find the link now, Is there much difference between different 2 pin LEDs then?

@DrDiettrich - I am actually having problems getting anything consistant at the moment so i will have a bit more of a play and try to upload a photo or circuit diagram. but im still unsure how i will later get this to work equally as well in both day and night situations and just being able to read a high/low signal!

With AC (capacitor) coupling of the amplifier you can catch all steep slopes, resulting from pulses of your sender diode. Such a signal can be fed into an digital input, causing interrupts if required.

TheGrovesY: @docdoc - Sorry i can't find the link now, Is there much difference between different 2 pin LEDs then?

Sure not, but you can't do much with only two pins, any active component require some power to run, i.e. three pins or more. Any IR sensor I have seen have 4 wires (2 for the transmitter, the LED, and 2 for phototransistor), or three if one is in common. So I wonder what kind of "LED" you're using.

If your receiver is a photodiode, you hook it up reverse biased in a divider and then take the signal from the junction between it and the resistor, see the attached schematic. I used a 1k in the divider.

My tutorial (I use the word loosely) may interest you.