Interfacing RF 433MHz Transmitter/Receiver Module with MCU

Interested in making your next DIY project wireless for the price of a cup of coffee? Then go with a 433MHz RF Transmitter and Receiver Module!

It is available online for less than two dollars, making it one of the most affordable data communication options available. And, best of all, this module is so small that you can incorporate it into almost any project.

Hardware Overview

Let’s take a closer look at the 433MHz RF Transmitter and Receiver Modules.

The Transmitter

This tiny module serves as the transmitter. It is as simple as it appears. At the core of the module is a SAW resonator tuned to operate at 433.xx MHz Apart from that, it has a switching transistor and some passive components.

• DATA pin accepts digital data to be transmitted.
• VCC provides power to the transmitter. Any positive DC voltage between 3.5V and 12V can be used.
• GND is the ground pin.
• Antenna is a pin that connects to the external antenna. To improve the range.

When a logic HIGH is applied to the DATA input, the oscillator runs producing a constant RF output carrier wave at 433 MHz and when the DATA input is taken to logic LOW, the oscillator stops. This technique is known as Amplitude Shift Keying.

The Receiver

• VCC provides power to the receiver. Unlike the transmitter, the receiver requires a 5V supply voltage.
• DATA pins output the received digital data. Both pins are internally linked, so you can use either one for data out.
• GND is the ground pin.
• Antenna is a pin that connects to the external antenna. To improve the range.

This one is a receiver module. It consists of an RF tuned circuit and a couple of OP Amps to amplify the received carrier wave from the transmitter.

It’s a lot like the Amplitude Modulation technique used in AM radio. Because it only has two levels, it is sometimes referred to as Binary Amplitude Shift Keying.

You can think of it as an ON/OFF switch.

• For logic 1 – the carrier wave is transmitted.
• For logic 0 – no signal is transmitted.

The RadioHead Packet

The RadioHead Packet is constructed as follows: At the start of each transmission, a 36 bit stream of “1” and “0” bit pairs known as a “Training Preamble” is sent. These bits are required for the receiver to adjust its gain before receiving actual data. Then a 12 bit “Start Symbol” is added, followed by the actual data (payload).

At the end of the packet, a Frame Check Sequence or CRC is added, which is recalculated by RadioHead at the receiver end, and if the CRC check is correct, the receiving device is alerted. If the CRC check fails, the packet is discarded.

This is what the RadioHead packet looks like:

        +---------------------------------------------------------------+
        |      36 Bits      |    12Bits    |   8Bits   |     16Bits     |
        +-------------------+--------------+-----------+----------------+
        |    Training       |     Start    |  Message  |      CRC       |
        |    Preamble       |    Symbol    |  Length   |                |
        +---------------------------------------------------------------+

Program Implementation

In this simple experiment, we will try to send a short text message from the transmitter to the receiver.

Here is the source to integrate your MCU.

I'm using STM32 Microcontroller. You can download source from here if you are using STM32L073 Nucleo board.