Ok so it's been a few months since the post on Interactive LED's. Even though I had already made a module and recorded a video, I had not had the time to upload the video or explain the circuit.
So below is a picture of the circuit in its most basic form. No LED protection for this simple circuit, however building more modules would require a far better design than the one shown...
InfraRed light emmitting from the IR LED transmitter is beamed onto an obstacle (your hand/finger etc.) and reflected onto the IR Receiver (a reverse biased IR LED) which triggers the amplifier to turn on the green LED's.
In the circuit I am using an LM324 - Low Power Quad Operational Amplifier. This is due to the fact that the reflected IR creates a small voltage on the receiver (depends on variables however one test I did was around 150-200mV) and approx 16x gain so 2.4-2.6V on the output.
Being a Quad OP Amp, I had 1 Green LED per output.
Because I only made this module as a "Proof of concept" I have not gone any further with it... Hopefully when I get some time I might come back to this...