Finding Stuff in the Sky

Continued from "Finding Stuff in the Sky" on GeekPhysical

As an artist and experimenter you may come across the problem of finding something or someone in your surroundings and needing to pointing some kind of sensor at them.

First, one needs to acquire an initial position, and thereafter retain a lock on the object need to be performed. One method of achieving the initial position is to first scan the whole space where the object may be located using the sensor(s) and then choosing the position with most/best sensor signal. Once the initial position is acquired a smaller part of the surroundings may be continuously scanned to retain knowledge of the position even if the object is moved.

Antenna tracker

We are doing long distance flights with RC video planes. During these flights a high-gain receiving antenna must be pointed directly at the aircraft. The antenna is mounted on a post with servos enabling it to pan and tilt in such a way that the whole sky can be pointed at.

A microcontroller system is then connected to the servos and a receiver measures the strength of the signal received by the antenna. Initially, the microcontroller has no knowledge of the aircraft position and needs to scan the sky for a suitable signal. Since the antenna is long and flexible it is desirable to use harmonic rather than abrupt movement thus the search pattern chosen is a spiral motion starting from an arbitrary point in the sky and moving outwards.

Once a position with sufficient signal is encountered along this spiral path this is chosen as the lock position. Hereafter the antenna is moved around the initial point in a smaller circle and the point with maximum signal strength is recorded. After each circulation the initial point is moved towards the maximum point. This results in the antenna continuously improving its aim towards the transmitter.

To prototype this system an LED was used as the transmitter and a photo transistor as the antenna/receiver. The LED was modulated to avoid interference from surrounding light sources.