light beam circuit

Description: This document outlines a straightforward process to transmit voice over a distance using amplitude modulation of light through sound vibrations. It details how modulated light is detected and demodulated by a receiver to reproduce sound. The experiments described are cost-effective and suitable for school laboratories or home settings. The interconnected computers that form the Internet rely on the ability to encode and decode information, such as voice or images, across various communication networks, including fiber optics and satellites. This process involves modulation for transmission and demodulation for retrieval. A modem, short for Modulator/Demodulator, performs these functions in computer systems. In radio broadcasts, modulation occurs at the transmitter, while demodulation takes place in the radio receiver. This article focuses on a basic modulation/demodulation process known as amplitude modulation, where sunlight is modulated to carry voice information. The experiments were inspired by the BBC2/Open University TV series "Rough Science," first aired in January 2004. The setup involves sunlight striking an aluminum foil diaphragm at the end of a tube, where sound waves cause the foil to vibrate, leading to variations in the angle of reflected light. This modulation results in a fuzzy light spot at a distance, with variations in amplitude corresponding to the sound waves. A light detector captures this modulated light, converting it into an electrical signal that can be amplified and output through a speaker. The transmitter requires direct sunlight, and the receiver must clearly see the light reflection. The tube can be made from various materials, with a diameter of 1-10 cm and a length of 10-50 cm, and experimentation with different diaphragm surfaces is encouraged. The detector plays a crucial role in converting light into electricity.

The described circuit involves a transmitter and a receiver, where the transmitter consists of a tube with an aluminum foil diaphragm at one end. When a voice is spoken into the tube, sound waves travel down the length of the tube, causing the diaphragm to vibrate. This vibration alters the angle of the light reflected from the diaphragm, resulting in amplitude modulation of the light beam. The light beam, when directed towards a receiver, carries the modulated information.

The receiver is equipped with a light detector, which may be a photodiode or a phototransistor, that captures the modulated light. The detector converts the light variations into an electrical signal, which is then amplified using an operational amplifier (op-amp) circuit. The output of the op-amp is connected to a speaker, which acts as a transducer, converting the amplified electrical signal back into audible sound.

To optimize the system, it is crucial to ensure that the transmitter is positioned to receive direct sunlight, and the receiver is aligned to capture the reflected light effectively. The use of different materials for the diaphragm, such as shiny gift wrapping foil or mirrors, can enhance the efficiency of the modulation process. The dimensions of the tube can also be varied to determine the best performance for the specific setup being utilized.

This project not only serves as an engaging experiment but also provides insight into fundamental concepts of amplitude modulation, light transmission, and sound reproduction, making it an excellent educational tool for understanding basic principles of electronics and communication systems.Here we describe a simple process to `put a voice on a sunbeam` and transmit it over a distance. It is a fascinating example of amplitude modulation of light using sound vibrations. We then describe how the modulated light is detected and demodulated in a receiver so that we can hear the sound. A wide range of physics and engineering experience ca n be learnt through these exciting `sunbeam` experiments. These activities are inexpensive and can be made in a school laboratory or at home. The interconnected computers forming the Information Super Highway (the Internet) depend on the ability to encode and decode information (e. g. a voice, picture or program) on the communication network. This network might be thousands of miles of wires, fibre optics, under sea cables or use satellites. Although this `information` may appear in an identical from on the distant computer there must be a large amount of encoding / decoding along the way, to make it all happen reliably.

The process of encoding information for transmission is called modulation and the subsequent information retrieval is called demodulation. On a computer system a `black box` does this job at either end of the network and is called a Modem (short for Modulator / Demodulator).

With other types of information communication, for example in radio broadcasts, the modulation of the programme is done at the transmitter and the demodulation performed within the radio receiver. In the following article however, we look at a more simple system which uses a most basic modulation / demodulation process called amplitude modulation.

We will learn about this process in an exciting and entertaining way. Bright sunlight (a sunbeam) will be modulated to carry voice information. Then, after sending it over a distance, we will demodulate it to be able to hear the sound. The experiments described here were one of the challenges for the popular BBC2 / Open University TV series - Rough Science - and the series were first transmitted in the UK in January 2004. In these experiments Sunlight strikes an aluminium foil diaphragm (or mirror, see `transmitter` section below) covering the end of a tube.

When you talk into the tube the sound waves travel down causing the foil to vibrate. The light hitting the foil would normally reflect off at an angle. But now additional constantly changing deviations in angle, take place which dependant on the amplitude and frequency of the foil diaphragm vibrations. At some distance away the reflected spot of light may appear slightly fuzzy instead of sharp because of this `modulation` movement.

If you take a small part of the spot its amplitude will vary over time. It will vary in exactly the same manor as the vibration of the foil due to the voice sound waves. The reflected light beam has therefore been amplitude modulated by the sound. If we arrange for a light detector to receive some of this modulated light its electrical output will vary (because of the amplitude modulation) in an identical way to that caused by the voice. When this is amplified and fed to a speaker (a transducer that converts electricity to sound) we hear the original sound once more!

In practice you need to arrange the transmitter reflector so that it receives a good source of direct sunlight and of course the receiver needs to be able to clearly see the reflection but it is really as simple as this! This is an open tube made from plastic, cardboard or metal having dimensions between 1-10cm diameter and 10-50cm long.

One end has a thin layer of aluminium foil taped over it. In practice all sorts of diameters and lengths need to be tried to find the most efficient for your set-up. You might also try other reflecting surfaces for the diaphragm, such as shinny gift wrapping foil, a mirror fixed to a rubber sheet etc.

The detector does the very important job of converting the light into electricity. The signal then needs to be amp