The NLOS Tx system is Extremely simple!


It uses a powerful LED which are still available on ebay very cheaply, the PT-54 Phlatlight which is a 10W LED on a pcb.
The ebay items are on a heatsink with lenses which are very useful as a starting point.


The LED is modulated with a carrier, i ended up on 1221Hz for no reason apart from not being on a 50Hz multiple, i have also the option to modulate it with JT65 tones.
The LED's run at ~2.5V so i started out with a fairly hefty fet, an IRFP450 to do the switching and a 2.5R drop resistor to allow use on 12v. This worked but things got a little hot!

The current system uses no drop resistors and a 5.5v PSU, the 0.5R on resistance of the FET is allowing it to run this way, but the PSU has a current limit set to 3A in case the FET fails S/C!
I'm currently running the LED at ~2A, it is capable of 8A continuous so there is a lot in store for the future.
With the standard lenses the beamwidth is probably 25degrees which is a little wide for what we need so i'm using another lens salvaged from an old projector to narrow the beamwidth to ~11degrees.
It's 60mmx70mm with focal length of about 140mm, i've attached this to a piece of tube for support and the LED with it's own lens is at the back of the tube at a distance so it illuminates most of the second lens.

Here's the arrangement:

Tx LED/Lens

LED on heatsink

Lens Illumination

This setup is then fitted into another tube to provide a shroud around the lens, we don't want too many neighbours wondering what the super bright red light is!

Tx with shroud on Pan/Tilt

You can also see i've put the light source on a pan/tilt head, this is far from original and now uses stepper motors, an Arduino and wifi interface for control.

Rx System
Tests