[م .نبيل زبن]

Building a computer controlled laser

Although computers got their name from their ability to calculate* one of the main uses for computers today is in communications.
Our modern telephone system is a large collection of computers* communicating with one another by sending pulses of laser light through optical fibers



We can do the same thing at home. In this project* we will build a laser transmitter that the computer will control* sending data by flashing the laser on and off. But we will eliminate the optical fibers* and just send the light through the air* in what is called free space laser data transmission.
The computer controlled laser data transmitter needs these parts:

A pocket laser pointer
We carry this item in our catalog.

A serial port connector
We use a 9 pin RS232 connector. You can take apart an old serial cable* or buy a new connector from an electronics or computer store. We carry this item in our catalog.

An NPN transistor
Almost any type will do* such as the 2N4401 or 2N2222A. We carry this item in our catalog.

A 470 ohm resistor
This resistor will have color codes Yellow Purple Brown and Gold. We carry this item in our catalog.

A light emitting diode
We use a clear lensed red LED* but most any LED will do. We carry this item in our catalog.

A generic printed circuit board
This is not really required* but makes assembly easier. We use the Radio Shack 276-159B. We carry this item in our catalog.

An alligator test lead
This is a piece of wire with alligator clips at each end. We used half of a red one and half of a black one* to make it easy to describe how to connect them* but a single test lead cut in half will do nicely. It does not harm the laser to connect them wrong -- just switch them around if the laser doesn't light up. We carry this item in our catalog.

A nine volt battery clip
This is a clip on connector for a 9 volt battery. We carry this item in our catalog.

A spring-type clothes pin

A screw or nail about 2 inches long with a flat head

A small block of wood for a base

A nine volt battery

A bit of tape and glue to hold it all together


Modifications to the laser


We will not actually modify the laser* so it will be easy to undo the project and still have a working laser pointer. But we will be removing the batteries* taping down the ON switch* and inserting a small screw where the batteries were* to make it easy to connect the laser to the transmitter circuit we will build



With the batteries removed* we can look into the back end of the laser and see the small spring that normally connects to the negative terminal of the battery.
We can also see the switch that turns the laser on — it is the little black box with the red button.



To make it easier to connect the little spring to our circuit* we will wrap some tape around a small screw* and place the screw head against the spring. The tape will be wound around the screw until it makes a snug fit inside the laser* compressing the screw a little bit



Next* we use some tape to hold the ON button down. We will be turning the laser on and off with our circuit* so the button will no longer be used* and must remain in the ON position at all times


The computer will communicate with our circuit through its serial port. If your computer does not have a serial port* there are inexpensive USB serial ports you can buy that will connect easily to your computer and will work fine for our project



We will use a 9 pin female serial connector* attaching wires to pins 4 and 5 only. Those pins are the Data Terminal Ready pin (pin 4) and the Ground pin (pin 5



We will use a generic printed circuit board for this project* although all of the parts could simply be soldered together without it* or even connected with alligator test leads. But soldering the parts to a printed circuit board makes the project sturdy* and guarantees the parts will stay connected



One side of the board has copper foil printed on it. The other side of the board will have our components. The two sides of the board are called the solder side (where we do the soldering) and the component side (where the transistor* LED* and resistor will be).
When we hold the board up to the light* we can see the shadow of the copper foil showing through on the component side