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TYPICAL APPLICATIONS

Figure 12 shows a circuit using the Linx LICAL-DEC-MS001 decoder. This chip

works with the LICAL-ENC-MS001 encoder to provide simple remote control

capabilities. The decoder will detect the transmission from the encoder, check for

errors, and if everything is correct, the encoder’s inputs will be replicated on the

decoder’s outputs. This makes sending key presses very easy.

Figure 13 shows a typical RS-232 circuit using the LR receiver and a Maxim

MAX232 chip. The LR will output a serial data stream and the MAX232 will

convert that to RS-232 compliant signals.

Figure 14 shows an example of combining the LR Series receiver with a Linx

SDM-USB-QS-S USB module. The LR will output a serial data stream and the

USB module will convert that to low-speed USB compliant signals.

GND

GND

VCC

NC

1

NC

2

NC

3

GND

4

VCC

5

PDN

6

RSSI

7

DATA

8

NC

9

NC

10

NC

11

NC

12

NC

13

NC

14

GND

15

ANT

16

RXM-LR

220

100k

D6

D7

SEL_BAUD0

SEL_BAUD1

GND

GND

LATCH

RX_CNTL

TX_ID

MODE_IND

D5

D4

D3

D2

VCC

VCC

D1

D0

DATA_IN

LEARN

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

LICAL-DEC-MS001

VCC

GND

GND

VCC

2.2k

10k

VCC

RELAY

SWITCHED OUTPUT

Figure 13: LR Receiver and MAX232 IC

C3

C4

C5

C1

C2

4.7uF

4.7uF

4.7uF

MAX232

4.7uF

DB-9

4.7uF

C1+

V+

C1-

C2+

V-

T2OUT

R2IN

GND

VCC

VCC

GND

GND

VCC

GND

GND

1

2

4

5

7

8

15

16

1

6

2

3

8

9

5

+

+

+

NC

NC

NC

NC

NC

NC

NC

NC

RSSI

C

DATA

ANT

GND

2

8

9

10

11

12

13

14

15

16

GND

VCC

RXM-XXX-LR-S

Figure 14: LR Receiver and Linx USB Module

NC

NC

NC

NC

NC

NC

NC

C

DATA

ANT

GND

1

2

9

10

11

12

13

14

15

16

GND

VCC

USBDP

USBDM

GND

DTR

TX_IND

VCC

SUSP_IND

RX_IND

485_TX

RI

1

2

3

4

5

6

7

8

15

16

USB-B

5V

DAT -

DAT+

GND

GND

GND

4

GND

SDM-USB-QS-S

RXM-XXX-LR-S

Figure 12: LR Receiver and MS Decoder

PROTOCOL GUIDELINES

While many RF solutions impose data formatting and balancing requirements,

Linx RF modules do not encode or packetize the signal content in any manner.

The received signal will be affected by such factors as noise, edge jitter, and

interference, but it is not purposefully manipulated or altered by the modules.

This gives the designer tremendous flexibility for protocol design and interface.

Despite this transparency and ease of use, it must be recognized that there are

distinct differences between a wired and a wireless environment. Issues such as

interference and contention must be understood and allowed for in the design

process. To learn more about protocol considerations, we suggest you read Linx

Application Note AN-00160.

Errors from interference or changing signal conditions can cause corruption of

the data packet, so it is generally wise to structure the data being sent into small

packets. This allows errors to be managed without affecting large amounts of

data. A simple checksum or CRC could be used for basic error detection. Once

an error is detected, the protocol designer may wish to simply discard the corrupt

data or implement a more sophisticated scheme to correct it.

INTERFERENCE CONSIDERATIONS

The RF spectrum is crowded and the potential for conflict with other unwanted

sources of RF is very real. While all RF products are at risk from interference, its

effects can be minimized by better understanding its characteristics.

Interference may come from internal or external sources. The first step is to

eliminate interference from noise sources on the board. This means paying

careful attention to layout, grounding, filtering, and bypassing in order to

eliminate all radiated and conducted interference paths. For many products, this

is straightforward; however, products containing components such as switching

power supplies, motors, crystals, and other potential sources of noise must be

approached with care. Comparing your own design with a Linx evaluation board

can help to determine if and at what level design-specific interference is present.

External interference can manifest itself in a variety of ways. Low-level

interference will produce noise and hashing on the output and reduce the link’s

overall range.

High-level interference is caused by nearby products sharing the same

frequency or from near-band high-power devices. It can even come from your

own products if more than one transmitter is active in the same area. It is

important to remember that only one transmitter at a time can occupy a

frequency, regardless of the coding of the transmitted signal. This type of

interference is less common than those mentioned previously, but in severe

cases it can prevent all useful function of the affected device.

Although technically it is not interference, multipath is also a factor to be

understood. Multipath is a term used to refer to the signal cancellation effects

that occur when RF waves arrive at the receiver in different phase relationships.

This effect is a particularly significant factor in interior environments where

objects provide many different signal reflection paths. Multipath cancellation

results in lowered signal levels at the receiver and, thus, shorter useful distances

for the link.