This project follows the work in developing and implementing an optical communication channel between two points, in an x-y co-ordinate scanning lock acquisition mode using controlled pan/tilt positioning units. To facilitate the data transfer the transmitter is required to locate the receiver as its position is unknown.

The transmitter scans the area in a set pattern to locate the receiver, when it locates the receiver, it is said to have ‘Locked On’. It is at this point that data is transmitted to the receiver which then acknowledges that it has received the data. The purpose of this project was to research and develop a demonstrator and prove the concept. The target application of the work is data transfer between two small mobile robots within a wider context of covert communications between autonomous vehicles. In these scenarios the likely data transfer will be co-ordinate data.

A custom pan and tilt head was developed using small remote controlled servo motors which could be controlled to move to any azimuth and elevation angle in a set region. The servos were controlled remotely using an FPGA integrated circuit which took commands from a host PC running a controlling program.

Initially communications development & experiments were carried out using a small red laser diode similar to those mounted in laser pens however this was later changed to using Infrared light emitting diodes (IR Led’s) for reasons of restricted implementation time and issues with the size of the receiver. Using IR led’s and a commercial IR decoder chip a communications channel was implemented using a common standard developed by Phillips called RC5 which is regularly used in television remote control’s. The transmitter and receiver were both controlled by PIC microcontrollers.

In order to allow the transmitter to locate the receiver, a concept was borrowed from the Nintendo Wii remote which has an camera based object tracker. The receiver was fitted with an IR Led which acted as a homing beacon. The pan/tilt head and transmitter was fitted with a standard miniature video camera linked to the controlling pc with a capture card. By using some image processing algorithms the location of the beacon and thus receiver could be determined, giving the system the ability to scan the area locate the receiver and transmit data. Using the beacon-to-camera path as a further communications channel, gave the scope of two way communication and in this project a basic data acknowledgement was implemented.

The project was successful in implementing the system and proving the concept of a point to point scanning optical communications channel. Tests were carried out and the working system was capable of locating the receiver and sending a small chunk of data followed by an acknowledgement of successful transmission at a distance of over 16m.