In many situations a communication link between to devices becomes essential. This communication can be wired or wireless. If two devices are close to each other (like a MCU and a Memory) a wired link is preferred. How ever in many situations two devices are reasonably far apart. In that case a wireless link is preferred. Two popular wireless communication technologies are

  1. IR Communications
    • Used in IrDA, and Remote controls
    • Short Range
    • Requires two devices to be in line of sight.
    • There should be no Opaque Obstacle in between the devices.
    • Easy and low cost to implement
  2. RF Communication
    • Widely used, including Bluetooth,Radios,Cell phones, Satellite etc
    • Wide range, from few meters to millions of kilometers (Can be Used to control Robots in Mars)
    • Does not requires two devices to be in line of sight.
    • Can cross many obstacles
    • Circuits can be complicated and costly.

In this tutorial we will learn how to practically implement a wireless link between two MCUs. This link will be used to send and receive digital data. We will create a Radio Frequency link. How ever as I said the RF circuits are little complicated so we will use ready made RF Modules. These are easily available and low cost.

What is a RF Module ?

A RF Module is a small circuit pre built and tested. They comes in Pair. One is RX or the receiver and other is a TX or Transmitter. The one we will be using is a low cost module of about Rs. 300 (US$ 6.00) per pair in India. They have reasonable range and works very good. Typical data rate is 1000 bits per seconds. You can buy them from the following links

RF Modules interfacing with microcontrollers

RF Modules


ASK RF Modules

RF Modules


As you can see they have very low pin count. This is because they are highly modular in design. The PINs are

  • TX
    1. Antenna
    2. Vcc (Positive Supply)
    3. DATA (Data Input)
    4. GND
  • RX
    1. Antenna
    2. GND
    3. GND
    4. Vcc (Positive Supply)
    5. Vcc (Positive Supply)
    6. DATA
    7. DATA
    8. GND

So you just need to apply power and fit an antenna and its ready to work. But the real "TRICK" is in sending and receiving data. And due to this many beginner fail to use them the first time (same thing happened with me too !). So I will revel the "TRICK" and give you a working example so that you can use these modules for many projects in the future.

Go to Part II


Avinash Gupta


Avinash Gupta is solely focused on free and high quality tutorial to make learning embedded system fun !

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