IR sensing

Hi, I am looking at starting a project which will combine this http://houseofanais.onsugar.com/limited-collection-glowing-furniture-Giancarlo-Zema-15504518 and http://www.youtube.com/watch?v=oKPUU21ReZg however in the format of a coffee table. I intend for the coffee table itself to have 3 - 4 "strips" of LEDs all controlled by an Arduino and these LEDs will react(become brighter etc.) when objects are placed on the table/moved around the table and would ideally start to sense the object from around 30/40cm above the table.

I am fairly new to the hardware-side and have only recently begun using Ardunio's. I have a couple weeks off coming up soon and I am hoping to use this as a project to keep me entertained during them! Plus if I don't manage to get this working then I will still have a nice coffee table to use!

So after having a look around at similar projects that people have completed it appears the most popular way is using IR Emitters and Receivers, which is the route I am intending to go down unless anyone can suggest a potential alternative. However when looking at these various projects/examples some people are using 2-pin IR photodiodes, some using 3-pin IR photodiodes and other places mentioning IR phototransistors which has generally left me fairly confused about what to use! So I have a couple of questions

  • 2-pin photodiodes VS 3-pin photodiodes: which one should I be looking at or is there not any real difference between the two?
  • photodiodes vs phototransistors: Again, which one should I be looking for/what are the differences? I am guessing phototransistors are a red herring?
  • LED modulation: I have seen IR sensors(I am guessing this is usually a synonym for a photodiode) with 38kHz advertised on them, I presume this means that I have to modulate my IR emitters to this frequency for the sensor/photodiode to see it, this being so the sensor doesn't become flooded with "normal" IR?

Many thanks,

Marc

LED modulation: I have seen IR sensors(I am guessing this is usually a synonym for a photodiode) with 38kHz advertised on them, I presume this means that I have to modulate my IR emitters to this frequency for the sensor/photodiode to see it, this being so the sensor doesn’t become flooded with “normal” IR?

Good observation, yes the emitter (IR 940nm LED, 2 legs) has to be modulated to 38khz, which is the standard frequency for most manufacturers remotes.
The receiver is a 3 legged device, usually 2.7v - 5.5v.

Photodiode = Light Emitting Diode. (2 legs)
Phototransistor = Light operated transistor. (3 legs)

Yes, use an IR receiver(3 pin) to receive signals & an IR LED (2 pin) to transmit the modulated IR signal.

The IRremote library is very good and also the IRLib library - both for Arduino.

To find out all about IR signals search google for the folllowing:

sb projects ir IRemote blog

If you proceed with this project, get a good quality IR receiver (we use Vishay components), there are different models for different applications, so you need to check the data sheet first.

Thanks JB_AU and AnalysIR! That has explained everything perfectly!

@AnalysIR, thank you for the additional links and info, that SB projects IR is a fantastic resource!