FM Remote Encoder/Decoder Circuit Working Principle and Applications

FM or RF communication is one of the best wireless communication systems to deliver the required service. In our previous article, we have discussed Different Types of Wireless Communications. The FM remote encoder and FM decoder circuit provide a secure RF communication between two devices (transmitter and receiver).

FM Remote Encoder/Decoder Circuit involves two main parts such as transmitter (encoder) section and receiver (decoder) section. This circuit built with an IC RF600E (encoder), IC RF600D (decoder) as its core part.

FM Remote Encoder and Decoder ICs

This FM Remote Encoder and FM Decoder circuit are used in many remote control applications. The RF600E and RF600D ICs are designed to achieve the maximum possible range from any radio or infrared transmitter-receiver set. They provide high security which prevents copying or grabbing while also obtaining the optimum range from the transmitter and receiver.

The devices are very easy to use and can be inserted directly into a circuit. The devices are very easy to use and can be inserted directly into a circuit. The RF600D has a feature enabling up to 7 unique RF600E encoder devices in standalone mode or up to 48 encoder devices when it is used in conjunction with an external EEPROM.

RF Encoder & FM Decoder IC’s
RF Encoder & FM Decoder IC’s

FM Encoder/ Transmitter Circuit

The FM remote Encoder system uses the frequency modulation technique for signal transmission. The transmitter circuit as shown below. IC1 RF600E and its other required components are connected as per the diagram. The pins 1 to 4 is connected to 4 switches individually.

FM Remote Encoder Circuit
FM Remote Encoder Circuit

These switches are associated with the inputs for IC1. When each input push button switch is pressed a corresponding code will be generated at the pin number 6 which is the data output pin.


This encoded signal available at pin 6 is buffered using the transistor Q1. And further, it is fed to the input of a general purpose FM transmitter module (M1) which is to be transmitted.

FM Encoder IC – RF600E

Pin Description:

RF600E IC available in 8 pin DIP. The pin description is given below.

Pin Number Name Description
1 S0 Switch input 0
2 S1 Switch input 1
3 S2 Switch input 2
4 S3 Switch input 3
5 Vss Ground reference Connection
6 OP Data output
7 LED Cathode connection for directly driving LED during transmission
8 Vcc Positive supply voltage connection


These are the switch inputs. We operate them to wake up the RF600E and cause transmission. They switched directly to Vcc.

Vcc / Vss

The power supply needs to be a stable and regulated voltage with <10mV ripple.

Note that in idle mode the transmitter current drain is typically only 100nA.


Data Output, this is a standard CMOS / TTL output that is further connected directly to the data input pin of the RF Module.


A direct LED drive with an internal current limit of typically 1 mA, operates when the RF600E is in transmitting mode.


  • 2.0-6.6V operation
  • Automatic Battery Level Monitor
  • ‘Manchester’ modulation
  • 8 pin DIP/SOIC package

FM Decoder/ Receiver Circuit

FM Decoder/ Receiver Circuit contains, the IC2 RF600D and its associated components. Pins 17, 18, 1 and 2 are the digital data output pins of RF600D corresponding to the input switches S1 to S4 of the encoder/transmitter circuits.

FM Remote Decoder Circuit- Stand Alone operation
FM Remote Decoder Circuit- Stand Alone operation

The digital data output pins 17,18,1 and 2 are asserted low when the relevant inputs S1 to S4 on the IC1 RF600E are asserted. Module M2 is a general purpose FM receiver module which receives the transmitted code through an antenna and fed it to the data input (pin 9) of the IC2.

Switch S6s can be used to select between latching and momentary digital output function. In latching mode, digital output pins (OP1 to OP4) are only asserted for the corresponding transmit signal. In latching mode, the output state is changed to each corresponding transmit signal.

The learn switch S5 is used to enter the decoder IC into the “learn mode”. Learn operation using the push button switch S5 is as follows.

  • Press and release the push button switch S5.
  • The status LED D2 will glow when S5 is pressed and will remain ON when S5 is released.
  • Operate the encoder/transmitter once.
  • The status LED D2 will become OFF.
  • Operate the encoder/transmitter again.
  • The status LED will start flashing.
  • When the flashing of status LED stops, the encoder will be successfully taught to the decoder and the transmitter/encoder will now operate the receiver/decoder system.

Up to seven encoder/transmitters can be learnt to each RF600D. Pin 3 of IC2 is the transmitter low battery indicator output and pin 11 is the serial data output.

FM Decoder – RF600D

Pin Description:

RF600D IC available in 18 pin DIP. The pin description is given below.

Pin Number

Name Input / Output? Description
1 OP3 Out Data Output 3 (S2)
2 OP4 Out Data Output 4 (S3)
3 LB Out Low Battery pin-goes Low when Low Battery Valid
4 Vcc In Positive supply voltage connection
5 Vss In Connect to GND
6 ECS Out Connects to EEPROM ‘CS’ pin
7 ECLK Out Connects to EEPROM ‘CLK’ pin.

Also, sets the data mark.

8 EDAT In / Out Connects to EEPROM ‘Data’ pin
9 IN In RF / IR Data input
10 LRN In Learn / Erase Switch Input & Status LED Drive
11 SD1 Out Serial Data output
12 LKIN In Option Link Input for Momentary or Latched outputs
13 SLEEP In High = Run, Low = Sleep Mode
14 Vcc In Positive supply voltage connection
15 Unused N/A No Connection
16 Unused N/A No Connection
17 OP1 Out Data Output 1 (S0)
18 OP2 Out Data Output 2 (S1)


  • 18 pin DIP/SOIC package
  • 4 Digital Outputs (15 States)
  • Asynchronous serial interface
  • 4.5V – 5.5V operation

Applications of FM Remote Encoder and Decoder

  • General Purpose Remote Control
  • Automotive alarm systems
  • Gate and garage openers
  • Electronic door locks
  • Identity tokens
  • Burglar alarm systems

I hope this article given the brief information on FM remote encoder/decoder, RF600E IC and RF600D IC. Furthermore, for any queries regarding this article or for any help in implementing Electrical and electronics projects, you can contact us or comment in the comment section given below.