Constructing a DIY laser modem

All digital communication finally comes right down to transmitting ones and zeroes, however there are various methods to attain that. One can encode that binary knowledge as modulation in a radio sign or just pulse electrical energy via a wire. However some of the attention-grabbing strategies is optical. Flashing a light-weight is a good way to transmit knowledge over lengthy distances at excessive velocity. Fiber optic cables are the most typical medium, however it is usually attainable to shine mild via open air. To exhibit this idea, Nino Ivanov constructed his personal laser modem.

In concept, this ought to be a really simple gadget: simply level a laser at a photoresistor. Pulse the laser in order that it’s on for ones and off for zeroes. Then measure the resistance of the photoresistor to learn these ones and zeroes. However as Ivanov explains, there are two points with this setup. The primary is that photoresistors are sluggish to answer mild adjustments and that severely limits the info transmission velocity. The second difficulty is that it isn’t all the time apparent what’s a zero bit (no mild) and what’s an absence of information transmission altogether.

Fortunately, laptop scientists solved the second difficulty many many years in the past. There are a number of transmission protocols that make the most of tips like parity bits and handshakes to make sure synchronicity. Ivanov was capable of make the most of these methods for half-duplex laser communication together with his customized {hardware} setup. That {hardware} consists of two Arduino Nano boards (one for either side of the communication), two pink 650nm solid-state laser diodes, and two photoresistors. Ivanov wasn’t capable of overcome the sluggish transmission time — there isn’t a overcoming the physics of ordinary photoresistors and Ivanov didn’t need to swap to costlier photodetectors.

Because it stands, this laser modem can transmit round 10 bits per second. That’s very sluggish, however this undertaking remains to be a enjoyable approach to experiment with laser knowledge transmission. If you wish to play with quicker speeds, specialised photodiodes for the telecom trade can detect optical indicators modulated at a number of gigahertz — although they’re fairly costly.