The circuit is built to receive signals from a standard Sony remote control and send the code bytes(2) received to an RS-232 port. It should not be difficult to adapt this to any particular IR remote control. The Sony was chosen because I happen to have a Sony VCR handy. An attempt to make it work with an old Philips unit resulted in the discovery that this used a different protocol for which I did not have any documentation.

Circuit Description

Circuit diagram in Postscript(28K)

This is probably the simplest PIC circuit I've ever put together. The Sharp IR module GP1U52X does all the hard work - it senses the IR signal and sends out the unmodulated signal. The most important thing is to ground the metal case of this module. The most important thing is to ground the metal case of this module. The most important thing is to... you get the picture. The PIC does the rest. It then sends the received code on what passes for an RS 232 line to the PC. The PC has a simple Visual Basic program which translates the received code and displays the corresponding function in big letters. In other words, I haven't found a useful application for this yet. Eventually, I plan to use it to run my future model railroad.

The pin connections are for a 6 pin connector on the PCB and have the following functions.

    Pin 1    Not used
    Pin 2    +5V
    Pin 3    Gnd
    Pin 4    RS-232 Rx
    Pin 5    RS-232 Tx
    Pin 6    External Reset

The PIC software consists of three files - ctrlir.asm which contains the IR bitstream decoding logic, ctrlcomm.asm which contains the logic for handling RS-232 I/O and the corresponding include file ctrlcomm.h. Some macros and values are defined in reg84.h. These assembly file listings were created using a PIC assembly to HTML converter. You can download the source as a single zip file.

Like most of my programs, this one operates around having a periodic interrupt, in this case one every 104us. This is used as a time base for everything including the serial I/O. The serial I/O works at 1200 baud and this interrupt rate gives 8 interrupts per bit.

The interrupt routine also reads the IR input. This gives a sampling rate of one every 104us. For the Sony remote control, the header lasts about 2500us, a mark lasts 1200us and a space 600us. Thus, the sampling rate is sufficient. The ISR checks the state of the IR input and increments a register CurrTime, for every interrupt where the state is unchanged. After a 0/1, a 1/0 and a 0/1 transition, it puts the number of ticks during the mark state and the space state into two registers MarkTime and SpacTime. It also sets a flag indicating that a bit is ready. The main routine then checks the values and identifies the bit value. This is then shifted into a 16 bit word in CodeByt1 and CodeByt2. When the end of transmission is detected by sensing a very long space, the entire code is transmitted on the serial port by the main routine. The actual transmission is done by the serial port ISR which is called once every two interrupts or every 208us.

These routines are the first assembly listings I have published on the web. Most of my assembly programming has been done in isolation. I would welcome any comments/criticism on any aspect of the program.

Construction

I haven't designed a PCB for this circuit. It is trivial enough to be built on a piece of veroboard. Have I mentioned that the case of the Sharp module must be grounded?

Front-end Software

This is a rudimentary Visual Basic program which gets the two bytes for each code from the PIC on the RS-232 port and displays them as hex digits. If the function exists in the lookup table held in the program then the function is displayed in large characters. You can download the source and executable for this program.

Updated on 6 Jan 98. Feedback to