Speech Communication using Laser

Light offers the fastest path for transmission of signals in comparison to any other medium. The circuit “Speech Communication using Laser” makes use of this aspect, it is a one or two-way optical communications system using a short-wavelength visible laser diode (say, RLT6505 or the laser module of a laser pointer) as the light-emitting element, free space as the transmission media and a light-dependent resistor as the light-receiving element. This system is a perfect medium for speech communication between two adjacent offices or between homes on the opposite sides of a road.

System description of Speech Communication Using Laser

The project “Speech Communication using Laser” can be used as both; one-way or two-way communication with slight modifications in the circuit. The block diagram of the Speech Communication using Laser for one-way speech communication is shown in fig. 1. It comprises a transmitter, receiver, and a common DC power supply section. The power supply section, at one end of the link, provides regulated 6V to the receiver-transmitter circuit. For two-way communication, you need to use an identical system, with the positions of the receiver and the transmitter reversed, with this system.

Transmitter Circuit | Speech Communication using Laser

In the transmitter section, the intensity of the laser beam is modulated by the output of an always-on code oscillator (operating at 10-15 kHz). Using a push to-on switch, the tone oscillator (operating at 1-2 kHz) is momentarily activated to alert the person at the receiver end before starting a voice communication using the microphone.

Receiver Circuit | Speech Communication using Laser

The receiver receives the intensity-modulated light signals through a light sensor and outputs the code and 1kHz tone/voice.

The circuit for detecting the code signal is built around a phase-locked loop (PLL-1). The absence of the code signal indicates interception of the laser beam and activates an audio-visual warning at the remote receiver. For detecting the 1kHz call/tone signal, another phase-locked loop (PLL-2) is used. The call detection is indicated by a buzzer sound and an LED.

Check out more other interesting projects using Laser, posted on bestengineeringprojects.com

1. Laser-Based Communication Link
2. Mini Laser Turret
3. LASER Demonstration Program using C
4. Laser Voice Transmitter Circuit

PARTS LIST OF SPEECH COMMUNICATION USING LASER

Resistors (all ¼-watt, ± 5% Carbon unless stated otherwise)

R1, R19, R20, R27, R32 = 1 KΩ R2 – R5 = 5.6 KΩ R6, R8, R18, R21, R28 = 8.2 KΩ R7, R12 = 15 KΩ R9 = 22 Ω R10 = 2 KΩ R11 = 68 Ω R13, R17, R26 = 2.2 KΩ R14 = 2.7 KΩ R15 = 390 Ω R16 = 390 KΩ R22 = 33 KΩ R23 = 4.7 Ω R24 = 36 KΩ R25 = 560 KΩ R29 = 4.7 KΩ R30 = 220 Ω R31 = 10 KΩ VR1 = 47 KΩ Preset VR2 = 100 KΩ Preset VR ­3 = 10 KΩ Potmeter VR4 = 5 KΩ Preset VR5, VR6 = 10 KΩ Preset VR7 = 100 KΩ Potmeter (LOG.)

Capacitors

C1 = 2200 µF, 25V (Electrolytic Capacitor) C2, C12, C13, C40 = 100 µF, 16V (Electrolytic Capacitor) C3, C5, C6, C9, C19, C22, C32, C35 = 0.01 µF (Ceramic Disc) C4 = 3.3 nF (Ceramic Disc) C7, C10, C11, C14, C15, C17, C20, C26, C29 = 0.1 µF (Ceramic Disc) C8, C36, C38 = 470 µF, 16V (Electrolytic Capacitor) C16 = 56 pF (Ceramic Disc) C18, C27, C33, C39 = 10 µF, 16V (Electrolytic Capacitor) C21, C24 = 2.2 µF, 16V (Electrolytic Capacitor) C23, C28 = 0.22 µF (Ceramic Disc) C25 = 1 nF (Ceramic Disc) C30 = 47 µF, 16V (Electrolytic Capacitor) C31 = 1 µF, 16V (Electrolytic Capacitor) C34 = 6.8 µF, 16V (Electrolytic Capacitor) C37 = 3.3 µF, 16V (Electrolytic Capacitor)

Semiconductors

IC1 = 7806, (6V Series Voltage Regulator IC IC2, IC3, IC7, IC8 = NE555 (Timer IC) IC4 = LM386 (Low power audio amplifier) IC5, IC6 = NE567 (Phase-locked loop) IC9 = CD4033 (Decade Counter/7-segment Decoder) IC10 = UM66 (Melody generator) BR1 = 1A Bridge rectifier D1 = 1N4001 (Rectifier diode) ZD1 = 3.3 V Zener diode LED1 – LED3 = 5mm red LED DIS1 = LTS543 (Common-cathode display)

Miscellaneous

SW1, SW2 = Push-to-on tactile switch LS1, LS2 = 8-Ω 1W speakers MIC1 = Condenser microphone PZ1 =Piezo buzzer X1 = 230V AC primary to 0-9V, 500mA secondary transformer Laser Module