HT12D Decoder

The HT12D decoder is a CMOS LSI for remote control system applications. It will interface to RF receiver modules to create a secure single or multiple channel RF remote control receiver. The decoder receives serial addresses and data from a programmed encoder that are transmitted by a carrier using an RF or an IR transmission medium. The decoder compares the serial input data three times continuously with its local addresses. If no error or unmatched codes are found, the input data codes are decoded and then transferred to the output pins. The VT pin also goes high to indicate a valid transmission. The HT12D decoder is capable of decoding information that consist of N bits of address and 12-N bits of data. The HT12D is arranged to provide 8 address bits and 4 data bits.

Features:

• Operating voltage: 2.4V~12V
• Low power and high noise immunity CMOS technology
• Low standby current
• Capable of decoding 12 bits of information
• Binary address setting
• Received codes are checked 3 times
• Address/Data number combination: 8 address bits and 4 data bits
• Built-in oscillator needs only 5% resistor
• Valid transmission indicator
• Easy interface with an RF or an infrared transmission medium
• Minimal external components
• Secure and robust protocol
• Ideal for remote control and security applications
• Compatible with the HT12E encoder IC
• 18-pin DIP
• Applications
• Burglar alarm system
• Smoke and fire alarm system
• Garage door controllers
• Car door controllers
• Car alarm system
• Security system
• Cordless telephones

Pin Diagram and Description:

• VDD and VSS are  used to provide power to the IC, Positive and Negative of the power supply respectively. As I said earlier its operating voltage can be in the range 2.4V to 12V
• OSC1 and OSC2 are used to connect external resistor for internal oscillator of HT12D. OSC1 is the oscillator input pin and OSC2 is the oscillator output pin as shown in the figure below.

• A0 – A7 are the address input pins. Status of these pins should match with status of address pin in HT12E (used in transmitter) to receive the data. These pins can be connected to VSS or left open.
• DIN is the serial data input pin and can be connected to a RF receiver output.
• D8 – D11 are the data output pins. Status of these pins can be VSS or VDD depending upon the received serial data through pin DIN.
• VT stand for Valid Transmission. This output pin will be HIGH when valid data is available at D8 – D11 data output pins.

Working of HT12D:

HT12D decoder will be in standby mode initially ie, oscillator is disabled and a HIGH on DIN pin activates the oscillator. Thus the oscillator will be active when the decoder receives data transmitted by an encoder. The device starts decoding the input address and data. The decoder matches the received address three times continuously with the local address given to pin A0 – A7. If all matches, data bits are decoded and output pins D8 – D11 are activated. This valid data is indicated by making the pin VT (Valid Transmission) HIGH. This will continue till the address code becomes incorrect or no signal is received.

PRACTICAL CIRCUIT OF HT12D:

Download HT12D:Here