Let's connect two computers over the air with a cheap radio transmitter and receiver and transmit some meaningful data, such as files.
Necessary
- - a computer (or two computers),
- - FS1000A radio transmitter and XY-MK-5V radio receiver (or similar),
- - two converters USB-UART (or computer COM port),
- - connecting wires.
Instructions
Step 1
We will be using an FS1000A transmitter and an XY-MK-5V receiver. Their price in an online store, if ordered in China, is less than $ 1, which, you see, makes them very, very attractive for home experiments.
Brief technical characteristics of the FS1000A transmitter:
- supply voltage - 3, 5 … 12 volts;
- operating frequency - 433, 92 MHz;
- transmission distance - from 20 to 200 meters (depending on supply voltage and environment).
- transmitter power - 10 mW.
Brief technical characteristics of the XY-MK-5V radio receiver:
- supply voltage - 5 volts;
- consumed current - 4 mA;
- signal frequency - 433, 92 MHz.
The modules come out of the box without antennas, so you have to make and solder them yourself. Antennas can be made from copper wire 17.3 cm long. This length corresponds to a quarter of the wavelength of the transmitted signal and the maximum antenna efficiency. They should be soldered to special contact pads, which are marked on the modules with the ANT marking.
Step 2
Now I will explain the essence of the idea. We will transmit a digital serial signal over a radio channel from one computer to another. The data will be fed to the radio transmitter using a conventional USB-UART converter (or a computer COM port). We will also receive data from the radio using a USB-UART converter.
Step 3
Let's put together the circuit. This is how it might look.
If you don't have a second computer, it doesn't matter, you can use one. The transmitter and receiver will be on different serial ports.
Step 4
Now on the computer to which the receiver module is connected, use a serial port monitor to connect to the port with a USB-UART converter. You will see constant noise received from the air. The fact is that at a frequency of 933, 92 MHz, most household appliances that use a radio channel transmit. These are security systems, weather sensors, automatic gates, etc. The receiver is trying to amplify the signal and therefore only amplifies the noise. When our transmitter starts transmitting, it will exceed the surrounding noise, and the receiver will be able to receive it. Of course, the distance between the receiver and the transmitter matters, as well as what objects or walls are between them. These will attenuate the signal and can lead to errors in the reception data.
Step 5
On the computer to which the transmitter is connected, using any terminal program, let's transfer any file to the port of our UART converter. Received data has changed in the receiver port monitor. But it's hard enough to figure out where the noise ends and the payload begins.
To extract data from the noise, one of the simple solutions is to write a number of zeros at the beginning and at the end of the file. The illustration shows that it is not difficult to separate the noise from the data in this case.
