Let's use LED and laser for optical communication!
There are various ways to convey the sound far away, but this time we will put it in the light. Please see the principle of optical fiber along with this experiment.
you need : LED, carbon resistance 10Ω, 100Ω, 3V battery, radio cassette player, solar cell, amplifier, speaker
First of all, on the calling side, I will explain how to send the voice to the other party by putting it on the light. The sound from the sound source is converted into the intensity of light by a modulation circuit. Just connect the LED etc. If you use laser light, the sound will be clearer. Also, although it is possible in principle with a miniature bulb,
As shown in the photo above, the sound is applied to both ends of the resistor 10Ω from the earphone terminal of the sound source such as a radio cassette player. Turn on the 3V power so that the LED lights up. A 100Ω resistor is inserted as the LED limiting resistor (described later), but if the LED does not burn out, it is possible without it. Now the audio is on the LED light.
On the receiving side, the solar cell receives the audio signal (laser light or LED light). At this time, please turn off the lights in the room. Solar cells pick up the light from fluorescent lights and disturb the audio signal. The audio signal is very weak, so put in an amplifier to amplify it. You can hear it as sound by connecting it from the amplifier to the speaker.
Even with LEDs, you can reach the edge of the classroom. If it is a laser, it will be transmitted even better. Currently, optical fiber (Experiment 725 Optical Fiber Principle) is used to efficiently communicate in the optical fiber instead of in the air.
LED limit voltage current: If you don't know , think about 3V-20mA .LEDs last a long time, but they break quickly when a voltage or current exceeding the allowable value is applied. If an LED with a current limit of 2.2V-20mA is connected to a 3V power supply, it will be consumed with a resistance of 0.8V-20mA. The resistance is 0.8 / 0.02 = 40Ω. Considering some error, I put a 100Ω limiting resistor in the circuit diagram.
how to read the color code of the resistor
black 0 brown 1 red 2 orange 3 yellow 4 green 5 blue 6 purple 7 gray 8 white 9 .
If the color code is 3 colors, enter a number in ①②③ .
For example, yellow, purple, brown, and silver are 47 x 10 squared, which is 470Ω.
(Represents a gold error of 5% and a silver error of 10%.)In the case of 4 colors, the first 3 are 3-digit numbers and the 4th is the factorial.