Egon - Tiny USB-connected IR Receiver for Remote Control of PC

Content:   Introduction - Features - A bit of theory - Hardware -Programing of SMD AVR - Software - EventGhost - Download


Complete receiver:
Egon_top.jpg (64kB)

Bottom view:
Egon_bottom.jpg (40kB)

Introduction

While studying methods of infrared remote control, on the web I discovered an interesting software EventGhost, primarily aimed at remote control of PCs. However, it has much more features than just that, so I decided to make full use of it.
Of course, I know the famous IgorPlug-USB receiver by Igor Češko, but that was not suitable for my intentions. In case of IgorPlug-USB, most of the funcionality is at the PC side; and as I don't program in Windows, it is like a "blackbox" for me - I don't understand how it works and I cannot modify it.
My intention was also to have a construction free of any licence fee, nag-screens and similar. So I have based my solution on the FT232RL USB-to-serial convertor, which has a free VCP (virtual serial port) driver available.
The resulting receiver, Egon, is presented here.

Features

Tiny, simple, minimum of parts, single-sided PCB
Configurable using terminal emulator program
Current version "understands" 17 different IR protocols (e.g. RC5 etc.)
Analysis mode for unknown protocols

A bit of theory and terminology

In order to comprehensibly describe functions of Egon, first, we have to briefly discuss the principles of infrared remote control. We will not go unnecessarily deep into details - there is enough information on this topic on the web.
When a button is pressed on the remote controller, its infrared LED emits an (for the bare eye invisible) light signal. Several informations are encoded in this signal. The method how this information is encoded is given by the protocol used. There are tens of such protocols in usage. The probably most widespread protocol is RC5 by Philips. Basically, there are two informations contained in the signal: address and command. Commands are mostly related to the pressed button. Address is a number, which distinguishes remote controls using the same protocol.
As in the common ambient there are many significant sources of infrared light possibly interfering with the remote control signal, a method for distinguishing this signal has to be used. The solution is to "chop" the the signal using a suitable carrier frequency. Common carrier frequencies range in 30kHz to 56kHz. As receivers, specialized integrated circuits are used, integrating a photodiode, preamplifier, bandpass filter and an output shaping circuit on a single chip.
Let's call "telegram" a single waveform which is transmitted when a button is pressed. As in the idle state the LED is not transmitting, each telegram starts and ends by a pulse. In fact, this is not a single pulse but a burst of pulses of the carrier frequency. Depending on the used protocol, there are several bursts and spaces in a telegram. In some protocols, sum of them is constant, in others this number changes.

Hardware of Egon, assembling and testing

After connecting the finished Egon to PC, the FT232RL has to be configured. From FTDI's webpages, download the VCP driver and configuration utility Mprog. After installing the driver, start Mprog and perform the configuration according to this picture:
Mprog.jpg (105kB)

Programming ATmega8 in SMD package

Description of software (firmware) and function

In order that Egon could properly receive and understand an IR telegram, it has to "measure" the lengths of all bursts and spaces. For time measurement, Timer 0 is used, with prescaler set to 256. So, as the processor clock is 6MHz, the timer increments in 42,7µs steps (this determines the resolution) and overflows after more than 10ms.
In the current version, Egon can receive 17 different protocols. I have assigned each protocol a number - for example, 0 for RC5, 2 for JVC, 3 for NEC etc. If the received telegram is recognized, Egon sends a unique identifier of this telegram to PC. Each identifier has 3 bytes, which are sent in the following order:
1) Protocol number
2) Command (button) number
3) Address of remote controller

If the ASCII mode is chosen (see details later), each byte is transmitted as two hexadecimal digits; and the identifier is terminated by the CR, LF (line end).
Egon has two basic modes of operation and several optional settings. When switched on for the first time, it is in the normal mode and is set optimally for EventGhost. It uses the following fixed communication settings: 57600 Bd, 8 bits, 1 stopbit, no parity, no handshake.
Although Egon communicates via USB, thanks to the drivers it behaves exactly if it would be connected to serial port. It means, that for communication with, and setting up Egon, any terminal emulator program (which can be set to the above parameters) can be used.
Each command starts by an asterisk (*) followed by capital letters. Any other character is ignored. The following picture illustrates how Egon responds to the *HELP command:
Help608x334.png (7kB)
There are two types of commands: Temporary commands, and Configuration commands. As their name indicates, the first type of commands act only temporarily, while the second type is permanent (until an opposite command is entered), even after removal of power (configuration is written into EEPROM).
In the following, all the available commands (listed also on the HELP page) are explained:

*HELP

This command displays the helppage as above.

*BUFFER

Buffer608x121.png (2kB)
This command prints out the current content of memory (buffer), which stores data from the received telegram. First byte is the total number of subseqent bursts and spaces. Second byte is the length of first burst, third is the length of first space etc. In the given example, the telegram has 19 (= 13 hexadecimally) bursts and spaces. First burst lasted for about 853µs (20 * 42,7), while the length of the first space was about 896µs (21 * 42,7).
The last identifier Egon transmitted just before the *BUFFER command is "001105". It means, that this was an RC5-protocol command number 11 (hexadecimally), and the address was 5.

*EEPROM

Eeprom608x255.png (5kB)
The *EEPROM command is to be used to control the content of internal EEPROM of ATMega8. In the given example, most of the memory is unused. Most of the used space is taken up by definition of commands (data string beginning by 07, 41 and ending by 50, 00).
The byte in red circle (09) contains Egon's configuration. The area in green circle at the end of EEPROM memory is the "Chip Erase Counter", where the Bootloader stores how many times the chip has been erased. In the given example, the counter contains 55 (0037 hexadecimally).

*STATUS

Status608x190.png (2kB)
Using this command, the current configuration of Egon can be checked.

*VERSION

Version608x144.png (3kB)
Egon responds to command *VERSION by displaying its identification including the version of SW. The homepage of Egon is displayed, too.

*TIMING and *NORMAL

TimNorm608x254.png (6kB)
When analyzing an unknown IR protocol, several IR telegrams have to be recorded. This is the purpose of *TIMING command. As shown above, after entering this command the prompt changes to "Timing first buffer ...". After the first IR telegram is received, the prompt changes to "Timing second buffer ...". After the second buffer is filled, both buffers are displayed and the prompt changes to "Command ?". In this moment, Egon ignores all IR data and expects some command. Any command can be entered (e.g. *TIMING again), but returns to normal mode only after entering *NORMAL command.
The format of data displayed after *TIMING command is almost the same than that described by the *BUFFER command. This time, Timer 1 clocked at 6 MHz is used for timing measurement. Length of each burst and space is then displayed in 256 times higher precision, using two bytes.
The explanation, why are there two buffers read and displayed, lies in the fact, that in some of the protocols, when a button is pressed for second time, instead of repeating the telegram a special command is sent. With only a single buffer, it would be difficult to capture this special command.

*UPDATE

Update608x68.png (1kB)
Purpose of this command is obvious - use it to upgrade Egon's firmware. Above, Egon's response is displayed. The characters under "Update firmware ..." are displayed by the bootloader running and waiting for AVRProg. After entering this command, close the terminal emulator program (to release the port) and start AVRProg. The bootloader waits for AVRProg for approx. 10 seconds, after which returns to Egon's firmware (performs a standard reset). For more details on the bootloader see my biprog programmer's pages.

*ASCII1 a *ASCII0

This couple of commands belong to the four (pairs of) configuration commands. If the ASCII parameter is OFF (after *ASCII0), Egon sends all identifiers, content of buffers and EEPROM, in binary form. This format is not suitable for displaying, but may be necessary for certain programs (e.g. Girder). However, EventGhost requires ASCII mode ON.

Note on the subsequent pictures, that after each configuration command Egon displays the current configuration status.

*SPACE1 a *SPACE0

Space608x282.png (3kB)
This command is valid only if ASCII parameter is ON. It enables to insert spaces between individual bytes of identifiers etc. For some, this mode is more readable, but when used with EventGhost, it is better to have SPACE mode OFF.

*RAW1 a *RAW0

Raw608x246.png (3kB)
When parameter RAW is ON, Egon transmits int PC both recognized and unrecognized telegrams. The format is identical to that described for *BUFFER command. In order that the RAW telegrams could be easily distinguished from recognized commands, one byte of "FF" (255 decimally) is inserted before the byte indicating the telegram's length.

*SUPPRESS1 a *SUPPRESS0

Suppress608x264.png (3kB)
The last parameter is SUPPRESS. It suppresses reporting of spurious short signals. Of course, this option is meaningless in other than RAW mode. When SUPRESS is OFF, even single bursts (with no spaces) are reported.

Egon and EventGhost

The best (free) software for remote control and automation of PC

About EventGhost

In my opinion, EventGhost is an extraordinary software. Primarily it is intended for remote control of PC, but can be used also for other purposes. Its most valuable feature is, that any function can be added, using Python scripts.

Setting EventGhost to cooperate with Egon

EG_001en.jpg (46kB)
After running the program, first, insert Serial port plugin into the configuration tree.
Click on the icon (or choose Edit - Insert Plugin ...), and the following window appears:
EG_002en.jpg (77kB)
To insert the plugin, click on Serial port and confirm using OK. The following dialog appears:
EG_003en.jpg (34kB)
Fill in as displayed here. Instead asterisk "*", as the event prefix, any word can be used. A short word is recommended, for example "Egon".
The Port item has to be filled in according to the settings of the FT232RL VCP driver.
When all the items are properly set, finish the dialog pressing OK. Since this moment, EventGhost should receive the remote control commands. Of course, the whole EventGhost application has to be properly configured, but such a description is beyond the scope of this document.

Download

To download the files, right click on the file name and choose Save target as ...".

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Last updated 16. 5. 2007

Translated by wek at efton dot sk