Make your own Remote Control

During the B. Tech course at NITK, Ohil and I had done a small project on Making a Remote Control as part of the Linear Integrated Circuits project. A little information on how remote controls work.

The use of Infra-red in the remote control technology was due to the fact that these could easily be blocked by walls, and a change of channel on our TV would not affect our neighbours in some way! Further, to ensure a distinct difference from the other objects which emit IR (the sun for example), the industry used these IR waves modulated over a 38KHz (36 to 40, and 56KHz are also seen) square wave.

What actually happens, is that a code is sent over this frequency using IR waves, which is decoded at the TV’s end. Multiple protocols exist to do the same. The JVC, Sony and Daewoo protocols are similar, and the other one RC5 protocol.

The JVC protocol has a pulse of approximately 600us followed by a space. Depending on the duration of the space, the bit is declared as a ‘0’ or a ‘1’. A longer space, around 1500us is a ‘1’ while a space duration of around 500us indiacates a ‘0’ bit.

The RC5 protocol uses this large duration space (1500us) to indicate a toggle of bit value. i.e. one will receive a pure square wave as long as there is no toggle.

Now, as far as the implementation goes, there are 2 parts to it. One is to actually know what are the codes transmitted (make a receiver) and the other to transmit these codes.

TSOP based IR Remote Control Receiver

Once connected to the computer, we could get the codes using a software called WinLIRC. More information on how to do this can be found at the LIRC website. Generally the first 4 hex digits would indicate a device code which would be common for all the buttons on the remote. The next 4 hex digits, (totally 8 hex digits = 32 bits) tell the actual code of the button.

Care needs to be taken to press the button lightly, only once, so as to obtain a clear indication of the code; else a repeat of the last 16 bits / entire 32 bits may be seen.

For the transmitter part of the remote control, one needs to generate the above codes given the press of a certain button, maybe using a micro-controller (Atmega-8) and then are to be simply “and”ed with a 38KHz square wave (555 timer – astable multivibrator). This signal needs to be fed to a 950nm IR LED. Note that an IR LED 920 – 980nm range would serve the purpose. This entire circuit will require a 5V supply though. So a battery pack (4 batteries) of 6V would be nice and compact.

This should give you a working remote control with all the functions that you would need. The best part is that you can now control multiple devices in your house with different codes being transmitted for different buttons.


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