Light Oriented Direction Finder

This project demonstrates how outer space probes can be guided to far distant places by star light received from a telescope.

The heart of this navigation system is a light detection system that can tell when the angle of tight received by the telescope has changed. Any change in light direction causes the thrust rockets to fire as required to keep the angle of light in the proper perspective. This action keeps the speeding space probe oriented always in the same position so that antennas, telescopes and thrust rockets can perform properly.

Hook up the circuit and place the circuit under a single source of light such as a desk lamp or single-lamp room light.

Adjust the 50K Control for a center-scale Meter reading.

Now tilt the project board so the light rays come from the CdS Cell side of the board. The Meter will indicate this position by deflecting up-scale.

Now tilt the project board so that the light rays come from the Solar Cell side of the board. The Meter will indicate this angle by deflecting down-scale.

All that is needed now is to use this change in Meter current to activate the proper control rockets, and the space ship would be repositioned to maintain the center-scale Meter reading. The circuit senses this change in light angle by using the change in relative light intensity on the Solar Cell and CdS Cell.

Greater light on the Solar Cell causes greater base-bias on the Transistor. Greater light on the CdS Cell causes a decrease in Transistor bias.

The Transistor bias controls the collector-to-emitter (C-E) voltage by amplification, so the small base-bias change results in a greater C-E voltage change.

Try using this circuit while walking toward a light source, holding the project board in front of you. Keep the board held against your stomach at a fixed position. Try holding different sides of the board against you until you find the one that gives the best sensitivity.

You may also want to try walking at angles which maintain Meter readings other than at the center. After some practice you should be able to navigate around the yard using this project and sunlight. Look out for shadows though, they can lead you astray!