Universal Programmable Remote Control
Cornell University, ECE 476
High Level Design
This project envisions a new generation of remote controls: ones that truly satisfy the demands of the modern consumer by adapting to each personís needs. The main feature of our product is its ability to record any other remote controlís signal and reproduce it at will. In this manner, our remote would be able to control several devices at the same time, and customize which button performs which action at its userís will. This allows the user to truly organize the actions it can perform with a single device both physically and logically: button organization and device/signal selection.
Our project was divided into several logical tasks: signal detection/recording, signal reproduction, and user interfacing. As mentioned, on our signal detection/recording phase we use an IR receiver to do analog demodulation of the signal emitted by the remote control. We then, via the Input Capture pin on the Mega32, record the widths of the 5 and 0V signals input from the receiver, and record them into memory. On our signal reproduction, we read from the values previously recorded and output a waveform modulated at 40 KHz by using timers and interrupts in the Mega32 processor. Our user interfacing consists of a keyboard and an LCD display; in order to read input from the user we constantly poll the keyboard using timers in the Mega32 processor and taking advantage of the ability of the ports to read and write to the same pin.
The main trade-off on our design was whether to stick to one standard, or to support more of them. The former was found far more desirable. The tradeoff wouldíve meant that the compactness of the recorded wave representation wouldíve been greatly improved had we decided to support only one, but given the nature of our product we decided that the latter was far more versatile and useful. Thus, we decided that recording the shape of the wave as opposed to the encoding that the wave would have represented on a given standard was the most effective way to go about implementing our product.
As mentioned before, there are several standards for infrared transmission; the ones for remote control communications include pulse coded, where the length of the pulses determine the unique signals, space coded (or RECS80), where the time between constant pulses are used, and shift coded (or RC-5), where all the pulses and times are constant but the direction of the transitions determine individual signals. Other standards include NEC, RC6. As mentioned before, our project is designed to support these standards, and any future standard whose carrier frequency is around 40 KHz. This is achieved by recording the shape of the wave, as opposed to the bits that are being transferred. Again, remote control signals are essentially digital signals that are either on or off, modulated with a carrier wave. They are not dependent on signal strength, for is they were, distance would affect their operation. More information on individual standards and the manufacturers that use them can be found on the websites registered within our references. By using time to dictate all digital signals, however, we are theoretically able to replicate an IR signal of any standard. We only tested ours on a Sony appliance, however, which uses the pulse coded standard.
All remote controls probably have patents on them, but that should not make our device illegal to use. This remote control may well be for a company that wants to make a universal remote control and have already bought up the rights to make the product. If it was for consumer use, the consumer needs to already have the remote, so duplicating it should not present any legal issues.