How to Design 100m RF Transmitter-Receiver Circuit with Microcontrollers for Secure Messaging

Hi everyone..

I'm a student at university of Dar es salaam, i have electronics project of sending message after coding it in microcontroller from RF transmitter to the RF receiver in a distance of about 100M, up to here i know i will use two microcontrollers, one at transmitter and another at receiver, RF modules(transmitter and receiver), and RF encoder and decoder but is optional and others electronics components such as resistors and capacitor. Now i need help to design first circuit diagram for that project or a link  for building electronics RF circuit interfacing with microcontroller. Microcontrollers will be used only to hide message with code to enable secure communication.

 

please i need your help..

The easiest way to do this would be to use a microcontroller with integrated wireless. If you are familiar with ARM processors there are many available. If you are just learning microcontrollers then you might find the ATMEGA2564RF or similar easier to work with.

http://www.atmel.com/devices/ATMEGA2564RFR2.aspx

This is an arduino compatible microcontroller with a built-in 2.4 ghz zigbee radio. You will still have to provide power and rf matching, but the datasheet provides all the information you need to do these designs. Atmel also provides application notes with a schematic checklist for the processor that will help you choose the capacitors, resistors and inductors (and possibly RF baluns and filters) needed to make this chip work.

As I recall, the RF output of the radio on this chip is 100 ohm differential, the standard designs use a balun to convert the signal to a 50 ohm (standard in most RF) single ended output. If you are not worried about getting regulatory approval, it is possible to construct a wire or PCB trace antenna that can be fed directly with the 100 ohm differential output (the two series capacitors would still be a good idea).

There are also boards around (AVR Butterfly I think) that implement these chips so you can purchase something off the shelf that has all the RF matching/antenna/etc. You can also take a look at the schematic for these boards to get an idea of how to do it yourself.

100M range should be achievable with these parts if the matching and antenna are done right.

Hi Kitundu

I suggest use of an RF transmitter and receiver module pair. You can use two microcontrollers, one connected to the receiver and the other connected to the transmitter.
A PIC can work and I generally prefer to use the 18F series.
An Arduino can also be used for this implementation. A very similar project which includes circuit diagrams and the source code which is similar to what you are searching for can be found at

http://www.nerdycoprojects.com/Projects.php

And look for a project where a robotic arm is controlled by a controller through an RF link. I hope this will be helpful