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This is an example of a basic remote control design utilizing a Holtek

encoder/decoder IC. When a key is pressed at the transmitter, a corresponding

pin at the receiver goes high. This basic circuit can be easily modified to suit

a broad range of applications, and clearly demonstrates the ease of using and

interfacing the Linx modules.

figure 8: Basic wireless encoder circuit

BASIC REMOTE CONTROL EXAMPLE

MODULATION REQUIREMENTS

The RM transmitter has a DC to 10 KHz modulation bandwidth and will accept

direct analog (AFSK) or digital data. A modulation lowpass filter (10 KHz @

-6 dB, 1st order) is used internally.

Digital data is normally input to pin 5 in a serial stream at CMOS logic levels

such as those from a microprocessor or encoder IC. The maximum data rate

is 10Kbps. The pin should always be driven with a voltage common to the

supply voltage present at pin 3 (Vcc). Under no condition should the voltage

at the data pin be allowed to exceed the supply voltage (Vcc).

DATA CODING

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

most effectively transfer data across it. Since the transmit and receive

modules have no internal digital coding/decoding, a user has tremendous

flexibility to send many types of analog and digital data. It is important to

understand, however, that some intelligent transmission structure must be

used. This is true for several reasons. The first and most significant is that

there must be some way to distinguish an intended transmission from

interferers and ambient noise. In addition, it is generally not possible to hold

DC levels across an RF link, therefore, transitions must take place at

minimum intervals.

It is, of course, a simple task to also accomplish application-specific data

encoding and transfer using a microprocessor. Inexpensive micros such as

the Microchip PIC series make an excellent choice for this task.

If you do not have a microprocessor on-board your product and you want to

send control signals such as a key press, switch closing, or low-rate data,

consider using an encoder and decoder IC chipset. These chips take care of

all encoding, error checking, and decoding functions and are available from

Linx. An example of such an application is shown below.