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Page 6

POWER SUPPLY REQUIREMENTS

The module does not have an internal voltage regulator; therefore it requires a

clean, well-regulated power source. While it is preferable to power the unit from

a battery, it can also be operated from a power supply as long as noise is less

than 20mV. Power supply noise can affect the

transmitter modulation; therefore, providing a clean

power supply for the module should be a high priority

during design.

A 10

Ω resistor in series with the supply followed by a

in cases where the quality of the supply is poor. Note

that the values may need to be adjusted depending

on the noise present on the supply line.

TRANSMITTING DATA

Once a reliable RF link has been established, the challenge becomes how to

effectively transfer data across it. While a properly designed RF link provides

reliable data transfer under most conditions, there are still distinct differences

from a wired link that must be addressed. Since the LR Series modules do not

incorporate internal encoding or decoding, a user has tremendous flexibility in

how data is handled.

If you want to transfer simple control or status signals, such as button presses or

switch closures, and your product does not have a microprocessor on board, or

you wish to avoid protocol development, consider using an encoder and decoder

IC set. These chips are available from a range of manufacturers, including Linx.

They take care of all encoding and decoding functions and generally provide a

number of data pins to which switches can be directly connected. In addition,

address bits are usually provided for security and to allow the addressing of

multiple units independently. These ICs are an excellent way to bring basic

remote control / status products to market quickly and inexpensively.

Additionally, it is a simple task to interface with inexpensive microprocessors,

such as the Microchip PIC, or one of many IR, remote control, or modem ICs.

It is always important to separate what types of transmissions are technically

possible from those that are legally allowable in the country of intended

operation. While the LR Series is ideally suited to the long range transfer of

control and command information, it can also be used with great success for the

transfer of true variable data such as temperature, pressure, or sensor data.

However, the 260 - 470MHz band in which the module operates is regulated by

Part 15, Section 231 of the FCC regulations. Many types of transmissions,

especially those involving automatic transmissions or variable data, may need to

be periodic. You may wish to review Application Notes AN-00125 and AN-00140

along with Part 15, Section 231 of the FCC regulations for further details on

acceptable transmission content in the Unites States.

Another area of consideration is that of data structure or protocol. The data

should be formatted in a predictable way and should be able to deal with errors

due to interference. This will ensure that the data is received and interpreted

correctly. If you are not familiar with the considerations for sending serial data in

a wireless environment, you will want to review Application Note AN-00160.

THE DATA INPUT

The CMOS-compatible data input on Pin 2 is normally supplied with a serial bit

stream from a microprocessor or encoder, but it can also be used with standard

UARTs.

When a logic ‘1’ is present on the DATA line and the PDN line is high, then the

Power Amplifier (PA) will be activated and the carrier frequency will be sent to

the antenna port. When a logic ‘0’ is present on the DATA line or the PDN line is

low, the PA is deactivated and the carrier is fully suppressed.

The DATA line should always be driven with a voltage that is common to the

to exceed the supply voltage, as permanent damage to the module could occur.

USING THE PDN PIN

The transmitter’s Power Down (PDN) line can be used to power down the

transmitter without the need for an external switch. It allows easy control of the

transmitter’s state from external components, such as a microcontroller. By

periodically activating the transmitter, sending data, then powering down, the

transmitter’s average current consumption can be greatly reduced, saving power

in battery operated applications.

The PDN line does not have an internal pull-up, so it will need to be pulled high

of 30

μA (10kΩ or less). When the PDN line is pulled to ground, the transmitter

will enter into a low-current (<5nA) power-down mode. When in this mode, the

transmitter will be completely off and cannot perform any function.

voltage source, such as a 5V microcontroller, an open collector line should be used or a

diode placed in series with the control line (anode toward the module). Either method

avoids damage to the module by preventing 5V from being placed on the PDN line while

allowing the line to be pulled low.

USING LADJ

The Level Adjust (LADJ) line allows the transmitter’s output power to be easily

adjusted for range control, lower power consumption, or to meet legal

value of the resistor determines the output power level. When LADJ is connected

4 on Page 3 shows a graph of the output power vs. LADJ resistance.

This line is very useful during FCC testing to compensate for antenna gain or

other product-specific issues that may cause the output power to exceed legal

limits. A variable resistor can be temporarily used so that the test lab can

precisely adjust the output power to the maximum level allowed by law. The

variable resistor’s value can be noted and a fixed resistor substituted for final

testing. Even in designs where attenuation is not anticipated, it is a good idea to

For more sophisticated designs, LADJ can be also controlled by a DAC or digital

potentiometer to allow precise and digitally variable output power control.

10

Ω

10

μF

Vcc IN

Vcc TO

MODULE

Figure 7: Supply Filter