مشاريع هندسيه لطلاب الهندسه الكهربائيه والالكترونيه

[م .نبيل زبن]

مشاريع هندسيه لطلاب الهندسه الكهربائيه والالكترونيه

Building a computer controlled radio transmitter


Building a computer controlled radio transmitter


How would you like to send text messages to your friends without wires* and without an Internet connection* and without paying monthly fees?
In this project we will build a very simple radio transmitter that you attach to a serial port on your computer. The computer then runs a free program that converts words you type into radio signals that are decoded by another computer* using a cheap radio receiver* and a sound card.
With a little study* you don't even need the second computer* since the radio signals are in Morse code* which anyone can learn to decode in their head with a little practice. It also comes in handy as a secret ********* or as a way to send long distance messages with a pocket mirror



Click on photo for a larger picture

The computer controlled transmitter needs these parts: (We carry most of the necessary parts in our catalog.)



A one megahertz oscillator
You can use other frequencies if you have a radio that can receive them. 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.

Some insulated wire for an antenna
Just about any kind of wire will do* the longer the better.

An alligator test lead
This is a piece of wire with alligator clips at each end. We carry this item in our catalog.


For our first transmitter* we will connect the parts with alligator clips. This lets us quickly change frequencies by replacing the 1 megahertz oscillator with an oscillator with a different frequency. Later we will show a version made with a socket for the oscillator* a printed circuit board* and a light emitting diode that flashes morse code along with the oscillator



Click on photo for a larger picture

The first step is to cut the test lead in half. In these photos I have cut two test leads* one red and one black* to make it easier to see where the connections go. But unless you are making two transmitters (your friend wants to send messages back* doesn't she?) you can just use one test lead (cut into two pieces).
Remove a little insulation from the cut ends of the wire* and solder one of the cut ends to pin 5 and the other to pin 4.