IRSky:
Manchester Decoder for RC6 and RC5 IR Remotes

Background

This project implements a Manchester Signal Processor with an associated RC6 and RC5 decoder. The software is written in C# and there are versions for Mono running on the Beaglebone Black and .NETMF on the Netduino Plus 2. The code is largely focused on interpreting the RC6 Mode 6 IR pulse codes sent by an SKY+ IR remote control - however it should work with minimal adaptation to interpreting the pulses sent by any RC5 or RC6 Philips TV IR remote control.

Why Write the IRSky Software?

One of the main things I would like to implement in my ongoing Wellity CNC router rehabilitation and modernization project is a Digital Read Out (DRO) and console. Besides displaying the usual position and status information, I would also like the console to be able to control the operations of the Wellity router. Basically I want a manual "jog" mode and also the ability to send commands back to the machine controller software on the PC (Mach 3) to invoke macros there. What is more, I want to be able to do all this with only minimal interaction with a computer keyboard.

So, in order to provide the part of the project that enables me to interact with the Wellity router in a keyboard free way, I have developed the IRSky software which will enable me to point a surplus SKY+ satellite box IR remote control at the console and have that console initiate actions based on the buttons being pressed. The choice of a SKY+ IR remote control is somewhat arbitrary being based on the facts that it a) has relatively few buttons, b) the buttons are big and hence suitable for my large shovel like peasant hands and c) I had one available.

The IRSky Software Hardware

The IRSky software runs on Mono running on the Beaglebone Black and .NETMF on the Netduino Plus 2 and expects, at minimum, an IR signal demodulator to be implemented to reduce the 38KHz IR carrier signal into pulses. I used the Sparkfun IR Receiver Breakout SEN-08554 for this and I must say it worked pretty well. You will also need to have some way of seeing which IR signals have been received once the software has decoded them. On the Netduino Plus2 I dumped these out to a Sparkfun 7-Segment Serial Display (COM-11442) via SPI and on the Beaglebone Black the code simply writes to the Console window.

Capabilities

• The IR pulses, suitably decoded from the 38KHz carrier, are input as digital square wave pulses of varying widths on a standard Beaglebone Black or Netduino Plus 2 GPIO pin.
• A software based Manchester signal decoder reads the pulses and records the rising and falling edges of the pulses as time intervals.
• Software decoders are implemented to interpret the time interval array and detect the presence of RC6 and RC5 signals within it.
• Once detected, the bits within the RC5 or RC6 signal are resolved and made publicly available to other routines.
• The full content of the transmitted RC5 and RC6 pulses is contained in a 4 byte Int32 value.
• All control, device, mode, trailer and information field content in the IR signal including the protocol type (RC5 or RC6) is present in the four output bytes.
• All processing is done within an interrupt into static fields. No objects are routinely created and destroyed to process the signal, hence overheads such as garbage collection are minimized.
• The code is written to be quite efficient in both memory and cpu requirements.
• The IRSky software can handle intermixed RC5 and RC6 signals.
• Tested on a Netduino Plus 2 and Beaglebone Black Rev C.
• The software is written in C#. Visual Studio 2010 projects are included with both the Netduino source code and the Beaglebone Black source code.
• If you are compiling for the Netduino Plus 2, the PC will require the Microsoft Micro Framework 4.2 to be installed.
• If you are compiling for the Beaglebone Black, you will need to have the BBBCSIO I/O library, C#, Mono and possibly a remote development environment configured.

What IRSky Software Does Not Do

The IRSky software is a Manchester Signal Processor. It does not have code which will interpret other types of IR Protocols such as the pulse width modulated Sony SIRC. Furthermore, the pulses processed by the Manchester processor are set to trigger on the 0.444 microsecond fundamental (1T) timing unit of the Philips RC5 and RC6 protocols. This value is a constant, easily adjustable in the code, and so other Manchester based signals could be implemented.

The code was developed for a SKY+ remote it has also been observed to work with a standard Sky remote but this was not extensively tested. No other types of RC5 or RC6 IR remote controls were tested.

Only the Decoders for the RC5 and RC6 Mode 6 protocols are included.

How it Works

Both the Netduino Plus 2 source code and the Beaglebone Black source code are extensively commented, however, a brief discussion of the function of each module is below:

The Manchester Decoder (ManchesterDecoder.cs NP2) or (ManchesterDecoder.cs BBB)
This code contains a function RecordPulseEvent which is called in an interrupt on both the rising and falling edge of the transmitted pulse of an IR receiver. This function records each pulse in an array. The code is designed such that one new sequential slot in the array will be created for each 0.444 microsecond 1T pulse width. Thus, if the current pulse edge was received 0.888 micro seconds after the previous one, it represents a 2T pulse width and two slots are used to record it in the array. The sign of the values in the array are also used to record information regarding whether the pulse was processed on a rising or falling edge. The incoming signals are continuously processed into the array of 1T values and the array is reset when it overflows or when some other external call (see below) resets it.

The RC6, RC5 Decoder (RC6RC5Decoder.cs NP2) or (RC6RC5Decoder.cs BBB)
Once the array of 1T signals reaches a specific length it is possible that it contains a valid and complete RC5 or RC6 signal. The array length is checked after every incoming pulse and if it reaches one of the specific trigger sizes, either the RC5 or RC6 decoder (it depends on the size) is called to scan the array for a valid byte sequence according to the protocol specification. Invalid sequences immediately reset the Manchester decoder, while valid sequences are processed into an Int32 value and made publicly available to other routines. The Manchester decoder is always reset after a valid signal is decoded. The RC6, RC5 Decoder will always overwrite the previous code - it does not queue the incoming pulses. However, there are flags and counters available which can indicate if a pulse was missed. Not that this matters much - no device expecting to be controlled by an IR Remote should expect to get every pulse sent to it. Fluorescent lights, in particular, chuck out a continuous stream of IR which can corrupt signals.

The Main Program (Program.cs NP2) or (Program.cs BBB)
This code serves as an example of how to set up the RC6, RC5 Decoder and Manchester Decoder for processing inbound pulses and how to process the output. The processed RC5 and RC6 signals from the IR remote control are made available at this level in the format below. The example code just strips out the information fields and sends that out as hex values over an SPI bus - but, obviously, in a real world example the output codes would be used the initiate other events.

 

The data in the IR signal will be presented as an Int32, the nibbles and bytes of which will have specific meanings dependent on the protocol being interpreted. The meaning of the various fields in the output Int32 is documented below. All diagrams are MSB to LSB, each [] is a byte and a pipe "|" is a nibble separator within a byte.

Output format for RC5 (most keys on SKY+ remotes in TV mode with Philips TV configured)
[protocol|0000][controlField][trailerField|0000][infoField]
  where
    protocol - 4 bit nibble hardcoded to RC5_PROTOCOLFLAG
    controlField - 8 bits of the control field information
    trailerField - 4 bit nibble which will be either 1 or 0
    infoField - 8 bits of information from the information field

Output format for RC6-6-20 (most keys on SKY+ remotes in SKY mode)
[protocol|modeField][controlField][trailerField|sField][infoField]
  where
    protocol - 4 bit nibble hardcoded to RC6_PROTOCOLFLAG
    modefield - 4 bit nibble with the mode number. will be 6 for RC6-6
    controlField - 8 bits of the control field information
    trailerField - 4 bit nibble which will be either 1 or 0
    sField - 4 bit nibble containing the sField info 0x0c for SKY+ remotes
    infoField - 8 bits of information from the information field

A Note On SKY+ Remotes in TV Mode

SKY+ IR remote controls operate in two modes: SKY mode and TV mode. SKY Mode is activated when the SKY button is pressed and most buttons will then emit IR codes which use the RC6-6-20 protocol. TV mode is activated when the TV button is pressed. The IR codes emitted in this mode are intended to control a TV, not the Sky box, and since TV's use a wide variety of IR protocols the codes output are dependent on the current TV setting of the SKY remote. If the SKY remote is configured to a Philips TV then the output codes will be RC5. It is up to the user to configure the Sky+ IR remote to the type of TV.

There are specific exceptions. Some buttons (Volume+/- and Mute) always emit the configured TV codes even in SKY mode. A few buttons (Play, Pause) send as yet unknown (to me) codes in TV mode and some buttons (TV Guide, Box Office) always toggle SKY mode back on and then send a SKY mode code.

If the remote has been configured to for use with a Philips TV, the IRSky software handles the intermixed RC6 and RC5 signals from the SKY+ IR remote control (Sky mode or TV mode). This is easily done using the 0081 four digit brand code.

The SKY+ IR Remote Control Codes page documents what I have been able to uncover about the codes sent by a SKY+ remote control.

License

This software is offered as source code under the terms of the MIT License.

Source Code

Web browsable versions of the IRSky Netduino Plus 2 Source Code and the the IRSky Beaglebone Black Source Code are available. The C# to HTML conversion was performed by the CoDocker software.

Download

• The version 01.00 zipped Netduino Plus 2 source code (19Kb).
• The version 01.00 zipped Beaglebone Black source code (19Kb).
• The Known bugs and ToDo List.
• The Version Change Log.

Acknowledgements

Various internet resources were used to help understand the RC5, RC6 and RC6 Mode 6 protocols. Especially useful was San Bergmans SB-Projects site which comprehensively documented the RC5 and RC6 IR protocols. Thanks San!

RC6 PROTOCOL
    http://www.sbprojects.com/knowledge/ir/rc6.php
    http://www.pcbheaven.com/userpages/The_Philips_RC6_Protocol/

RC6 MODE 6A PROTOCOL
    http://www.guiott.com/wrc/RC6-6.html

RC5 PROTOCOL
    http://www.sbprojects.com/knowledge/ir/rc5.php

NETDUINO
    User "Phil" on the Netduino forums has also provided a Manchester RC6 code which works with SKY+ remotes - however it does not handle RC5 so the TV mode specific buttons (such as Vol+, Vol- and Mute) cannot be recognized. http://forums.netduino.com/index.php?/topic/185-rc6-decoder-class/

Images

A SKY+ IR Remote Control