RF transmitter and Receiver circuit

  Whenever there is an input from the push button, it is received by the encoder (HT12E) as parallel data. It is converted to a serial data and sent to the transmitter. This data is modulated by the transmitter and sent at a frequency of 433MHz. The transmitted signal is picked up by the receiver at the same frequency as that of the transmitter and demodulated before being transferred to the decoder (HT12D). HT12D compares the serial input data three times continuously with the local addresses.

If no error or unmatched codes are found, the input data codes are decoded and then transferred to the

output pins. The “Valid Transmission” (VT) pin also goes high to indicate a valid transmission.

The decoder converts the received serial data back to its original form (parallel) so as to display the corresponding output with respect to the input signal at the encoders section.

COMPONENT DESCRIPTION

HT12E: This is a four channel encoder that receives input from the push button. It converts the parallel data from the push button to serial. It is made up of eight address bits and they must be configured same as the address bits of the decoder.

1MΩ RESISTOR: This is connected to the oscillator input and output pin of the encoder IC. It is used to set the oscillator frequency of the encoder IC.

10KΩ RESISTOR: Its function is to enable transmission of serial data to the transmitter and it configured in pull down mode.

51KΩ RESISTOR: This is connected to the oscillator input and output pin of the decoder IC. It is used to set the oscillator frequency of the decoder IC.

PUSH BUTTON: This allows for keying-in of input to the encoder.

REGULATOR (7805): This provides regulated +5v supply to the circuit. It receives its input from a 9V battery.

HT12D: This is a four channel decoder that receives input from the push button. It converts the serial data received to parallel data. It has eight address bits and they must be configured same as the address bits of the encoder.

LED: Outputs are displayed here according to corresponding input from the encoder.

RF MODULE: This comprises of an RF Transmitter and an RF Receiver. The transmitter/receiver pair operates at a frequency of 433MHz.

The Transmitter module has three pins namely Vcc, Din and ground.  The Vcc pin has an input range of voltage from 3V to 12V. The center pin is the data pin to which the signal to be transmitted is sent. This signal is then modulated using the ASK (Amplitude Shift Keying).

The Receiver module has four pins namely Vcc, Dout, Dout and Ground. The Vcc pin should be powered with a regulated 5V supply.