Laser Torch-Based Voice Transmitter & Receiver
by : Fahad Mirza | April 19, 2011 | 1 comments Skill Level: Beginner

Using this circuit you can communicate with your neighbors wirelessly!!!

Using this circuit you can communicate with your neighbors wirelessly. Instead of RF signals, light from a laser torch is used as the carrier in the circuit. The laser torch can transmit light up to a distance of about 500 meters. The phototransistor of the receiver must be accurately oriented towards the laser beam from the torch. If there is any obstruction in the path of the laser beam, no sound will be heard from the receiver.


The transmitter circuit (Fig. 1) comprises condenser microphone transistor amplifier BC548 (T1) followed by an opamp stage built around μA741 (IC1). The gain of the op-amp can be controlled with the help of 1-mega-ohm potmeter VR1. The AF output from IC1 is coupled to the base of transistor BD139 (T2), which, in turn, modulates the laser beam. The transmitter uses 9V power supply. However, the 3-volt laser torch (after removal of its battery) can be directly connected to the circuit—with the body of the torch connected to the emitter of BD139 and the spring-loaded lead protruding from inside the torch to circuit ground.


The receiver circuit (Fig. 2) uses an npn phototransistor as the light sensor that is followed by a two-stage transistor preamplifier and LM386-based audio power amplifier. The receiver does not need any complicated alignment. Just keep the phototransistor oriented towards the remote transmitter’s laser point and adjust the volume control for a clear sound. To avoid 50Hz hum noise in the speaker, keep the phototransistor away from AC light sources such as bulbs. The reflected sunlight, however, does not cause any problem. But the sensor should not directly face the sun.

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Taufique_ | Feb 3,2013 at 01:00 AM
Techshop should take attempt to make a bundled component package of this tutorial. I was hoping to make this as a fun project for my nephew, but it isn't always possible to pay a visit to Patuatuli. Would it be possible to provide a bundled component package for this? Maybe notify me through mail so that I can place an order in the shortest possible time?
Fahad | Feb 3,2013 at 01:47 AM
We are bringing this laser:
After we have the products we will let you know.

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