Remote Control Circuit Using FM Radio

In this post we will learn how to build a simple FM remote control circuit for toggling small AC loads such as lamps, fans etc using an ordinary FM transmitter circuit and a modified FM radio circuit.

This remote control system enables the user to get an ON/OFF control on any desired appliance, by simply modifying an existing radio into a remote receiver through a relay control circuitry.

Introduction

Remote control circuits are not so easy to build as they incorporate critical inductor stages and also, the components are difficult to procure.

However a simple homemade FM remote control can be made by modding your existing FM radio as the receiver part.

The transmitter can be simply made by assembling a few electronic components.

The two sections together can be used for controlling any electrical load remotely from any part of the house.

Making the FM Transmitter for the Remote Control Unit:

The figure shows a very simple FM configuration using one transistor and few other passive components.

Here the inductor becomes the most crucial part and must be made carefully as per the given instructions.

T1 along with the pF capacitors and the inductor forms the RF stage and is responsible for the generation and transmission of the RF carrier waves.

Using a Music Modulation for Increasing Transmitter range

The section consisting of the IC UM66 and the electrolytic capacitor forms the modulating stage and injects the required modulation signals to the RF stage.

This helps to make the transmitted waves much stronger and travel up to longer distances.

Once the assembly of the transmitter circuit is done, its working should be confirmed by switching ON the transmitter and by verifying the received signals over the FM radio.

The reception should consists the music from the UM66 IC and should be received by the radio, loud and clear even from a distance of over 30 meters.

After finishing the construction of the transmitter, you need to assemble the Flip Flop circuit by soldering the electronic components as per the shown diagram.

This stage will be later on required to be integrated with the modified FM radio.

How to Modify a FM Radio as a Remote Control Receiver for Controlling Electrical Gadgets

For this project you will need an ordinary FM radio for making the receiver/controller unit.

After procuring a FM radio, you will need to do the following modifications in it.

• Open the back cover of the FM radio to uncover the circuit of the unit.
• Now carefully, integrate the flip flop circuit to the speaker terminals of the radio. The connections won’t be difficult as everything’s shown in the diagram very clearly.
• The idea here is to use the reception audio from the radio speaker terminals and use it to activate our flip flop circuit and the relay.
• Switch ON the FM radio and tune to some vacant area where there’s no station available, and only the background “hissing” noise is audible.
• Adjust the volume control of the radio toward the maximum and you will find the LED light up, refine the adjustment until the LED just switches OFF.
• Now tune the radio to some station, without disturbing the volume control.
• You will find the LED flickering in response to the audio outputs.
• You will also see the flip flop responding appropriately and the relay switching randomly to the LED illuminations.

This concludes the procedures, your setting of the radio or the modifications of the radio is complete.

Testing the Remote Control Switching

Now switch ON the transmitter and once again tune the radio to the spot where it receives the transmitter music loud and clear.

That’s it, the setting of your home made remote control is complete.

Now as many time you click the transmitter switch, it will be received by the radio and the flip flop relay activated alternately.

The relay contacts may be wired to any appliance and may be controlled easily by your transmitter through mere clicks of its switch.

However the speaker of the radio will also make lot of noise and therefore to eliminate this you may just tear of the cone of the speaker so that it keeps silent, activating only the flip flop.