Electronic – Remote Control Design

IR Remote controls are generally designed to be tight to their functional requirement in order to keep their manufacturing cost extremely low. This generally means that the chip in the remote is a dedicated chip designed to produce a certain IR protocol that is specific to the manufacturer's device family.

Each key on the remote will cause a different IR modulated sequence to be sent to the target device. All of the key codes for that target device will be within the same IR protocol family. A protocol family will support a certain number of key codes within the protocol whether that be 32, 64 or 128 codes (or some other number). I mention this because some remotes can support multiple target devices for example TV, DVD etc. Each target device may be a different protocol family. There are handful of different protocol families in use and are generally lined up with major equipment manufacturers such as Sony, NEC, Philips and others.

It is highly unlikely that the remote that you have in hand will be easily convertible for use with your alternate target device. You would have to first know what IR protocol family was required for your target device and what the required individual key codes are. Unless you have the actual remote in hand this information is almost impossible to reverse engineer. The best you could hope for is that the family protocol and key codes may be documented off on some web site.

If you did manage to find the target device family protocol and key codes then the process of converting the existing device would only be successful if it natively supported the same IR family protocol. It is usually possible to reverse engineer the IR protocol and key codes for an in-hand IR remote control. Two general methods are used for this, both of which require the use of an oscilloscope. With one scheme you probe the signal in the remote itself that drives the transmit IR emitter LED. In the second scheme an IR receiver component can be rigged up on a proto-board and then used to receive the signal from the remote control which is then probed with the oscilloscope. The latter scheme is somewhat easier to see the IR signalling envelope because the IR receiver removes the carrier frequency from the detected IR stream. At the transmit side you would see this carrier as part of the waveform and is typically 36KHz, 38KHz or 40KHz although other carrier frequencies may be used by some IR protocol families.

In the long run you would probably be best off to look into finding a replacement remote control for your target device or look at universal replacement type controls that can be programmed to emulate the IR family protocols and key code sets for several thousand different target devices. Even if the universal remote does not directly support your target device it is possible to sometimes experiment with selecting alternate similar type device selections and find one that will allow partial control of your device.

No. Absolutely not. The "Last/Return/Previous Channel" button is a unique function code that the TV interprets!

For the most common IR control protocols, Philips' RC5, Sony's SIRC or NEC, the remote is normally an application-specific integrated circuit (ASIC) with hardcoded TV codes for fixed remotes or a microcontroller with a reprogrammable eeprom for learning remotes (programmed via special codes or through a programming interface like JP1 or even IR learning).

The remotes have a single code programmed into each button, and that does not change without intentional reprogramming. These codes are arbitrary for the remote and depend on the TV to interpret. You can see an example for Insignia TVs here: http://www.getzweb.net/jp1/data_returns/DeviceEFCs.php?type=TV&devid=1204&webpid=++396

Each of these codes are single function, unless you get into more advance macros which are a group of codes assigned to the same button that get sent in order.

Unlike some of the dubious test methods listed above, you can actually decode the actual code sent by your remote. All you need is a common IR receiver module and a microcontroller (MSP430, Arduino) or computer like the Raspberry PI.

Once you do, you will find that the "Previous" button will always send the same exact code, regardless of what channel you have switched to and when. The remote does not actively track what channel or ANYTHING you do.

A different way would be to use a IR Learning Remote like the Harmony remotes. If the previous button was an active copy of the last channels selected, then you could not clone the feature.

Further note, the On/Off button is typically a single code that the TV interprets as toggling the current state, but discrete On and discrete Off codes often exist for any given tv, as well as dedicated "Input Source X" button instead of "Next Input" type codes.