Designs, Ideas

In many conditions a communication link between devices becomes essential. This communication between the devices may be wired or wireless [17]. If two devices are close to each other a wired link is preferred over wireless. How ever in many situations two devices are far apart.In that case a wireless link is preferred.Following are the two popular wireless communication technologies:
4.1.1 IR Communication
Used in Remote controls and it is short range.Requires two devices to be in line of sight or close to each other.There should be no obstacle in between these devices.It is very easy and inexpensive low cost to implement.
4.1.2 RF Communication
Used in bluetooth, radios, cell phones, satellites etc. Wide range from few meters to millions of kilometers and it does not requires two devices to be in line of sight.It can cross many obstacles in its path.Its circuits may be complicated and costly.This link is used to send and receive digital data.However, as RF circuits are complicated, so we use RF Modules. These are easily available in markets and have low cost.
4.2 RF Module
RF Modules are used for wireless transfer of data. This makes them suitable for remote control applications as, where you need to control some machines or robots without getting in touch with them.Now depending upon the type of our project, the RF module is chosen. For short range wireless control applications, an ASK (Amplitude shift keying) RF Transmitter-Receiver Module of frequency 433 MHz is most suitable.It is quite compact and cheap.
4.3 RF Module (Transmitter & Receiver)
The RF module as the name suggested,operates at Radio Frequency. The corresponding frequency range varies between 30 kHz & 300 GHz [18]. In this RF system, the digital data is represented as variations in the amplitude of carrier wave. This type of modulation is known as Amplitude Shift Keying (ASK).Thus, transmission through RF is better than IR because of many reasons. Firstly, signals through RF can travel to larger distances making it suitable for long range applications while IR mostly operates in line of sight mode (short range), RF signals can travel even when there are obstacles between transmitter & receiver. Secondly RF transmission is more stronger and reliable than IR transmission [18]. RF communication uses a specific frequency unlike IR signals which are affected by other IR emitting sources.This RF module which is used in our project comprises of an RF Transmitter and an RF Receiver.RF Tx and Rx is shown in figure 4.1.
Figure 4.1 RF Transmitter and Receiver
4.4 RF Transmitter
The transmitter and receiver (Tx/Rx) pair operates at a frequency of 433 MHz .An RF transmitter transmits the data wirelessly. The transmission occurs at the rate of 1Kbps to 10Kbps.The transmitted data is than received by an RF receiver operating at the same frequency as that of the transmitter. The RF module is used along with a pair of encoder and decoder. The encoder is used for encoding parallel data for transmission feed while reception is decoded by a decoder.

4.4.1 Features of RF Tx
Some of its features are
• Operating frequency of433.92 MHz
• low cost
• 1.5-12V operation
• 11mA current consumption at 3V
• small and compact size