PLL Power-Down Function:

The PLL portion of the IC can be powered up and down through the control of the PD input (pin 14). During PLL power down operation (pin 14 pull low), the reference crystal oscillator, fixed VCO divider, PFD, and charge pump are all shut off and the current consumption of the IC drops by approximately 600 μA. The VCO circuitry remains on and may be configured to operate as a buffer amplifier for an external SAW-based oscillator.

Figure-4.3-Application circuit of RX3400

4.3

Antenna:-The antenna is also used at the receiver unit to collect the data which is send by the transmitting antenna. The antenna receives the desired signal and sends the data to the decoder circuit. For example, AMR devices for water meters must be able to communicate in the RF unfriendly environment of the iron water pit. Typically, this is accomplished by placing an antenna on top of the water pit lid, with the connection to the meter going through a hole in the lid. This allows a large antenna area, but the antenna often protrudes dangerously high above the lid, and requires a field-installed connection between the antenna and the water meter.

4.4.1

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- HT12D: 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

 Pair with Holtek’s 212 series of encoders

 18-pin DIP, 20-pin SOP package 4.4.2

Applications:- Burglar alarm system

 Smoke and fire alarm system

 Garage door controllers

Description:-The 2^12 decoders are a series of CMOS LSIs for remote control system applications. They are paired with Holtek’s 2^12 series of encoders (refer to the encoder/decoder cross reference table). For proper operation, a pair of encoder/decoder with the same number of addresses and data format should be

chosen. The decoders receive serial addresses and data from a programmed 2^12 series of encoders that are transmitted by a carrier using an RF or an IR transmission medium. They compare the serial input data three times continuously with their 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 2^12 series of decoders are capable of decoding informations that consist of N bits of address and 12-N bits of data. Of this series, the HT12D is arranged to provide 8 address bits and 4 data bits, and HT12F is used to decode 12 bits of address information. [10]

8-Address & 4-Data

Figure-4.4-Pin diagram of HT12D

Table-4.2-Pin description of HT12D

4.5 Seven Segment

Display:-A seven-segment display (abbreviation:"7-segment display"), less commonly known as a seven-segment indicator, is a form of electronic display device for displaying decimal numerals that is an alternative to the more complex dot-matrix displays. Seven-segment displays are widely used in digital clocks, electronic meters, and other electronic devices for displaying numerical information.

A seven segment display, as its name indicates, is composed of seven elements. Often the seven segments are arranged in an oblique, or italic, arrangement, which aids readability. The seven segments are arranged as a rectangle of two vertical segments on each side with one horizontal segment on the top and bottom.

Additionally, the seventh segment bisects the rectangle horizontally. There are also fourteen-segment displays and sixteen-segment displays (for full alphanumeric);

however, these have mostly been replaced by dot-matrix displays. In a simple LED package, each LED is typically connected with one terminal to its own pin on the outside of the package and the other LED terminal connected in common with all other LEDs in the device and brought out to a shared pin. This shared pin will then make up all of the cathodes (negative terminals) OR all of the anodes (positive terminals) of the LEDs in the device; and so will be either a "Common Cathode" or

"Common Anode" device depending how it is constructed. Hence a 7 segment plus DP package will only require nine pins to be present and connected. [15]

4.6 Microcontroller

AT89C2051:-The AT89C2051 is a low-voltage, high-performance CMOS 8-bit microcomputer with 2K bytes of Flash programmable and erasable read-only memory (PEROM). The device is manufactured using Atmel’s high-density nonvolatile memory technology and is compatible with the industry-standard MCS instruction set.

By combining a versatile 8-bit CPU with Flash on a monolithic chip, the Atmel AT89C2051 is a powerful microcomputer which provides a highly-flexible and cost-effective solution to many embedded control applications. The AT89C2051 provides the following standard features: 2K bytes of Flash, 128 bytes of RAM, 15 I/O lines, two 16-bit timer/counters, a five vector two-level interrupt architecture, a full duplex serial port, a precision analog comparator, on-chip oscillator and clock circuitry.

4.7 Display Driver

74LS244:-The 74LS244 is Octal Buffer and Line Driver designed to be employed as memory address drivers, clock drivers and bus-oriented transmitters/receivers which provide improved PC board density.

 Hysteresis at Inputs to Improve Noise Margins.

 3-State Outputs Drive Bus Lines or Buffer Memory Address Registers.

 Input Clamp Diodes Limit High-Speed Termination Effects.