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Analysis of IR remote control devices with an AVR ATmega8


This page demonstrates, how
  1. the signals of a remote control device are designed,
  2. the hardware for measuring them is designed,
  3. the software works,
  4. the measuring results are read out,
  5. the measured data can be analysed.

1. Design of remote control signals

To better discriminate remote control signals from other IR sources, such as light and heat generation, these signals are modulated. Remote control signals look like this:

IR-Signal

The duration of active and inactive states, the signal sequence, is specific for each remote control device, every producer has its own formula and design. Here are thousands of opportunities to make a difference, so don't wonder why all your different boxes don't interfere with any other device in your living room.

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2. Hardware for measuring

STK500 I used the STK500 for measuring and did not build up an own device for that purpose because the measuring is done only once and is not needed contineously.

TSOP1738 As IR sensor a TSOP1738 from Vishay Telefunken is used. This small device is placed into a socked, which is wired and connects via pin plugs to Port D of the STK500 (red=VTG, black=GND, gray=PD2).

ATmega8 As processor a ATmega8 is used that is inserted into the socket SCKT3200A2 of the STK500 and is programmed via the green ISP plug.

Port D The RS232 lines RXD and TXD are connected with Port D PD0 and PD1. On the SPARE connector, the RS232 signal can be connected with a computer.

Xtal Jumper The clock signal is generated with a Xtal of 9.8304 MHz, the jumpers and the ATmega8 fuses have to be set according to this.



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3. Software for measuring

The software for the ATmega8 is in HTML format here and in in asm format here available.

The software Send and receive over the serial interface are handled interrupt-driven to avoid interference with measuring signal durations.

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4. Reading the measuring results

The measured data doesn't have to be copied using paper and pencil. When using a brandnew and top-rated operating system like Windows 7, reading the data to a simple text file nowadays is a rather complicated issue. Because there is no free and functioning terminal program with a simple capture mode any more. It seems that operating systems today don't need this any more, ancient technologies!

Virtual XP I have found one for free, but it doesn't run on a W7-64bit. So I downloaded and installed a virtual PC and the WinXP of M$ first (a very intensive task).

Port selection Then I downloaded RealTerm frtom the internet and installed it inside VirtualXP. Before starting RealTerm the serial interface to the SPARE connector of the STK500 has to be plugged, in my case via a serial-to-USB device, and the USB connection has to be allocated to the VirtualXP.

In the RealTerm window the serial port (here: port 3) has to be assigned, as baudrate 38,400 selected and the button Change to be pressed.

Connect The ATmega8 displays his menu.

Data receive The data of high- and low-phases in mode A is measured with a 10 µs clock.

The window Capture in RealTerm allows to download the data of a remote control device to a text file. In order to do this, a filename has to be selected and Capture is started with the button. To collect all data of a remote control device in one file, you should input a name for the key first (by moving the cursor into the transmitting window of RealTerm and typing "key=xyz" and CarriageReturn).

Data So that is how this logged data looks like in your text file.

5. Analysing the logged data

To analyse this data in a comfortable way I have written a piece of software. Here you find a description and the software.

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