radio frequency transmitter and receiver module

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Introduction
In various industries we have to control various processes from various locations. In hazardous area we cannot enter. So on–off controlling and logging becomes complicated. To avoid this problem we have to think about wireless technology, i.e. we have to control the device without from remote area.
Our project does the same function. Our project is based on the radio frequency transmitter and receiver module In our project, the heart of the circuit is a rfask pair. RFASK receiver unit consist of 4 relays, which can control four different processes at a remote place by operating a keypad at a transmitter section. Any process can set ON for momentary or latched condition as per our requirement and mode setting provided.


KEYPAD INTERFACING:

This block consists of 5 SPST switches,4 switches to control the corresponding processes and one switch to reset the others. A SPST switch a push-to-make switch which returns to its normally open (off) position when you release the button, this is shown by the brackets around ON. This is the standard doorbell switch


General Description

The RCT-433-AS is ideal for remote control applications where low cost and longer range are required. The transmitter operates from a 1.5-12V supply, making it ideal for battery-powered applications. The transmitter employs a SAW-stabilized oscillator, ensuring accurate frequency control for best range performance. Output power and harmonic emissions are easy to control. The transmitter is basically a negative resistance LC oscillator whose center frequency is tightly controlled by a SAW resonator. SAW (Surface Acoustic Wave) resonators are fundamental frequency devices that resonate at frequencies much higher than crystals.


The HT12 encoders are a series of CMOS LSIs for remote control system applications. They are capable of encoding information which consists of 12/8 address bits and 4 data bits. Each address/ data input can be set to one of the two logic states. The programmed addresses/data are transmitted together with the header bits via an RF or an infrared transmission medium upon receipt of a trigger signal. The capability to select a TE trigger on the HT12E or a DATA trigger on the HT12A further enhances the application flexibility of the 212 series of encoders. For the HT12E encoders, transmission is enabled by applying a low signal to the TE pin.


Features
• Operating voltage
• 2.4V~12V for the HT12E
• Low power and high noise immunity CMOS technology
• Low standby current: 0.1_A (typ.) at
• VDD=5V
• Minimum transmission word
• Four words for the HT12E
• Built-in oscillator needs only 5% resistor


Relay driver circuit


A relay is an electrically operated switch. Current flowing through the coil of the relay creates the magnetic field which attracts a lever and changes the switch contacts. The coil current can be on or off so relays have to switch positions and they are double throw switches. Relays allow one circuit to switch a second circuit which can be completely separate from the first. For example a low voltage battery circuit can use a relay to switch a 230V ac mains circuit.