Optical fiber transmission voice circuit

This circuit can transmit speech through 1mm plastic optical cable. The transmitter circuit board (KIT26 T) has a microphone and a circuit to modulate the LED light. The LED is installed in a plastic shell to facilitate the connection to the FO optical cable for transmission. On the receiver (KIT26 R) board there are photoelectric receivers, speakers and circuits for converting the detected light signals into electrical signals, amplifying and converting them into sound waves. The speech signal is transmitted in the optical cable in the form of light waves and is not affected by any electric and magnetic fields. The transmission distance is long and the anti-interference ability is strong. Each circuit board requires a 9V battery, but it is recommended to use a rectifier power supply for continuous use. 4.3m of 1mm diameter plastic optical cable is installed in the device. This line can well transmit signals through 183m optical cable. Note: The plastic optical cable used here is not 1μm glass optical cable. Glass optical cable can communicate over a longer distance (about 32km). Plastic optical cable is very convenient for experimental application and has obvious anti-interference effect for short-distance communication in an electronic noise environment. This circuit is assembled on a single-sided printed circuit board.

Working principle: The audio signal is initially a sound wave, which is converted into an electrical signal by the electronic microphone of the transmitter. This signal is amplified by the audio amplifier composed of LM358, and with the help of a separate transistor to control the terminal voltage of the LED, the electrical signal is converted into a light signal. The light signal is sent to the plastic optical cable. At the other end of the optical cable, the light signal shines on the photoelectric tube of the receiver. The photoelectric tube converts it into an electrical signal. This signal is amplified and sent to the speaker to be converted into sound waves.

Transmitter component selection: IC1 uses LM358 integrated circuit. VQ1 uses BC547 transistor. C1 uses 0.1μF single capacitor. VD uses IF-E96 photoelectric transmitter (pink dots on blue background). Other components are shown in the figure.

Receiver component selection: VT uses IF-D93 photodetector (black background with red dots). C2, C3, CA, and C6 all use 0.1μF single capacitors. Other components are shown in the figure.

Transmitter PCB:

Photoelectric receiver: