RXM-315-LR_1 Datasheet, PDF (4/11 Pages) List of Unclassifed Manufacturers – LR SERIES RECEIVER MODULE DATA

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 significantly affect the receiver sensitivity,
therefore; providing clean power to the module should be a high priority during
design.
Vcc TO
A 10Ω resistor in series with the supply followed by a
MODULE
10µF tantalum capacitor from V_CC to ground will help
10Ω
in cases where the quality of the supply power is poor. ^{Vcc IN}
Operation from 4.3V to 5.2V requires an external
10μF
330Ω series resistor to prevent V_CC from exceeding
3.6V. These values may need to be adjusted
depending on the noise present on the supply line. ^{Figure 10: Supply Filter}
USING THE PDN PIN
The Power Down (PDN) line can be used to power down the receiver without the
need for an external switch. This line has an internal pull-up, so when it is held
high or simply left floating, the module will be active.
When the PDN line is pulled to ground, the receiver will enter into a low-current
(<40µA) power-down mode. During this time the receiver is off and cannot
perform any function. It may be useful to note that the startup time coming out of
power-down will be slightly less than when applying V_CC.
The PDN line allows easy control of the receiver state from external components,
like a microcontroller. By periodically activating the receiver, checking for data,
then powering down, the receiver’s average current consumption can be greatly
reduced, saving power in battery-operated applications.
Note: The voltage on the PDN line should not exceed V_CC. When used with a higher
voltage source, such as a 5V microcontroller, an open collector line should be used or a
diode placed in series with the control line. Either method will prevent damage to the
module by preventing 5V from being placed on the PDN line, while allowing the line to be
pulled low.
USING THE RSSI PIN
The receiver’s Received Signal Strength Indicator (RSSI) line serves a variety of
functions. This line has a dynamic range of 80dB (typical) and outputs a voltage
proportional to the incoming signal strength. It should be noted that the RSSI
levels and dynamic range will vary slightly from part to part. It is also important
to remember that RSSI output indicates the strength of any in-band RF energy
and not necessarily just that from the intended transmitter; therefore, it should be
used only to qualify the level and presence of a signal.
The RSSI output can be utilized during testing or even as a product feature to
assess interference and channel quality by looking at the RSSI level with all
intended transmitters shut off. The RSSI output can also be used in direction-
finding applications, although there are many potential perils to consider in such
systems. Finally, it can be used to save system power by “waking up” external
circuitry when a transmission is received or crosses a certain threshold. The
RSSI output feature adds tremendous versatility for the creative designer.
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THE DATA OUTPUT
The CMOS-compatible data output is normally used to drive a digital decoder IC
or a microprocessor that is performing the data decoding. In addition, the module
can be connected to an RS-232 level converter chip, like the MAX232, to a Linx
USB module for interfacing to a PC, or to a standard UART. Since a UART uses
high marking to indicate the absence of data, a designer using a UART may wish
to insert a logic inverter between the data output of the receiver and the UART.
The receiver’s output may appear to switch randomly in the absence of a
transmitter. This is a result of the receiver sensitivity being below the noise floor
of the board. This noise can be handled in software by implementing a noise-
tolerant protocol as described in Application Note AN-00160. If a software
solution is not appropriate, the squelch circuit in the figure below can be used
and the designer can make a compromise between noise level and range.
VCC
R2
500k
D1
RSSI
C1
R1
0.1μ
2M
DATA
VCC
VCC
2
-
3₊
8
1
U1
4 LMV393
R3
200k
1
3
R4
5M
Figure 11: LR Receiver and LS Decoder
VCC
5
2
U2
MAX4714
6
Squelched Data
RECEIVING DATA
Once an 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 modules do not incorporate internal
encoding / decoding, the user has tremendous flexibility in how data is handled.
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. Application Notes AN-00125 and AN-00140 should be reviewed along
with Part 15, Section 231 for further details on acceptable transmission content.
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 wide range of manufacturers including
Linx, Microchip, and Holtek. These chips 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 receivers independently. These ICs are an
excellent way to bring basic remote control / status products quickly and
inexpensively to market. Additionally, it is a simple task to interface with
inexpensive microprocessors such as the Microchip PIC or one of many IR,
remote control, DTMF, and modem ICs.
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