– 1 –

Introduction

As wireless systems have become more integrated and lower in cost,

more and more products are seeking a competitive edge through the

addition of remote control features. Despite this wireless explosion, there

is still some trepidation among product designers at the thought of

undertaking a wireless design. This application note discusses the basics

of remote control systems including legal and technical considerations.

Remote control is the act of controlling something from a distance.

Remote Keyless Entry (RKE) is a form of remote control in which the

device being controlled provides access to a secure location. A common

example of this type of system is an automotive door lock. The lock on

the car door is remotely controlled by a transmitter in a fob. Most

systems are unidirectional (one-way or simplex); however, new generation

technologies are now available for bidirectional (two-way or duplex)

communication.

System Conguration

A simple remote control system consists of an encoder, RF transmitter,

RF receiver and a decoder.

A Brief History

The encoder is generally connected to one or more buttons, switches or

contacts. The encoder detects the closure of one of the switches and

converts that into a digital data stream. This data is then sent to an RF

transmitter that conveys this data into free space. An RF receiver receives

the data and sends it to a decoder. The decoder analyzes the data and,

if it is valid, replicates the switch closure on an output. This output is then

connected to whatever circuitry is to be controlled. With that basic over-

view of the system, a more detailed look at the system components can

be undertaken.

The Basics of Remote Control and Remote Keyless Entry

Application Note AN-00320

Revised 11/06/12

Figure 1: A Basic Remote Control System

– 2 –

Application Note AN-00320

Radio Considerations

When considering a radio for the system, legal considerations are just as

important as technical considerations. Various governments regulate the

radio spectrum within their countries and specify what can and cannot be

done at a particular frequency. Understanding the legal requirements in

the countries in which the end product will be sold is the ﬁrst place to

start when choosing a radio.

Fortunately, many governments have recognized the advantages of

globally consistent regulations, so the requirements for remote control

systems tend to fall into two camps. The United States Federal

Communications Commission (FCC) has speciﬁed the 260MHz to

470MHz band to be used for the transmission of command and control

data. There are a number of requirements and restrictions in this band

that are intended to keep it clear of interference. Linx Application Note

AN-00125 goes into the regulations in this band in detail. Canada and

Brazil have adopted regulations that are very close to the US regulations.

315MHz and 433.92MHz are the most common frequencies for RKE in

those countries.

The European Union has adopted a different set of regulations, but these

regulations are followed by all member countries and several Paciﬁc and

Asian countries. Europe has allocated the 433.05MHz to 434.79MHz

band for remote control and command applications. Since this band is

so narrow, the center of the band (433.92MHz) is typically chosen so that

products still fall within the band over temperature and component

variations.

This frequency overlaps the FCC band, meaning a single 433.92MHz

radio design can be used in the U.S. and Europe. This makes hardware

design and manufacturing efﬁcient, but it also makes the band crowded

with devices. It is up to the designer to understand the regulations and

determine the best frequency of operation for their product.

Once the radio’s frequency is chosen based on the legal regulations, the

radio type and modulation method can be chosen. The two most

common types of modulation for RKE devices are On-Off-Key (OOK) and

Frequency Shift Key (FSK) modulation.

OOK modulation represents a logic ‘1’ by turning the RF carrier on and a

logic ‘0’ by turning the RF carrier off.

Figure 2: OOK Modulation