The project has 4 main goals;
1. Cheap - it has to be cheap to make as you can buy expensive remote fob testers already.
2. I wanted to get a level of signal to identify a weak performing remote (which has possibly cropped up in the forum previously).
3. I wanted to see the data that is sent from the key, something decodable will prove the fob is in good working order.
4. Software will have to run on the Lexia laptop (Windows XP with USB ports).
The solution costs less than £10 (including antenna) and will decode the key data and show a level of signal on the screen. I uses my lexia laptop and TV Dongle as the receiver. The added benefit is the USB Dongle will also play digital TV and radio programs but that is not covered here
The fob tester consists of my lexia laptop running windows XP, a USB SDR TV Dongle, an aerial and some free software Microsoft .NET framework 3.5, SDR# and RTL-433-WIN32 (Thanks to Megavoid for the windows port of Benjamin Larssons (merbanan on github) rtl-433 software).
How its made
Disconnect the Actia/Lexia/Diagbox from the computer.
Buy one of these USB SDR dongle from eBay, which includes an aerial and drivers but DO NOT install the drivers from the CD. Other USB SDRs do work with the software and some don't.
The original SDR USB is difficult to get now, but the compatibility has improved.
I have tested this one and know it works for this job. Connect it to a windows XP laptop (now Diagbox runs on WIn7, so plug it into your windows 7 laptop), the one that runs lexia was Ideal for me. Let windows attempt and probably fail to install its own bulk drivers and do not use the ones on the CD. Attach the aerial to the USB.
This one works, other may not.
The laptop needs Microsoft .NET 3.5 to run SDR Sharp (SDR#) so download .NET 3.5 from microsoft.com and install it if you don't already have it.
Download and install SDR Sharp from sdrsharp.com.
Unzip the sdr-install.zip to a folder of your choice, but remember what your choice was.
In the folder you will find install.bat, run this and allow to install to complete.
You may get a warning from your antivirus about HTTPGET, do not act on this and allow HTTPGET to download the latest version of SD sharp.
Plug in the USB dongle without the supplied CD, use the windows bulk drivers.
Finish the wizard and ignore any error messages
With SDR# installed and the USB SDR dongle plugged in, run the file zadiag_xp.exe which is found in the newly created sdrsharp folder.
press 'Install Driver' when 'Bulk-in Interface' has been selected in the drop-down list.
(There are some very clear instructions on this step here) if you need them
This will get SDR sharp working, you can test this now if you like by double clicking SDRSharp.exe (Blue square icon) found in the newly created sdr-install folder.
Ensure RTL-SDR / USB is selected in the Source list on the left.
Tune the software to 433.902.000 (433.902MHz) and press the triangle in the top left of the window.
The triangle icon starts the software running and it is then actively monitoring 433.902Mhz for signals. If you press your fob button within range of the aerial the screen will show a blue rise in the graph and the red/orange part will record the signal change as its scrolls. The height of the blue bar in the top screen is directly proportional to the amplitude of the signal (range).
The second part of the project is to detect the bits of data as data and decode them to further prove the remote fob is functioning correctly. To decode the signal I used a program written to decode weather station remote units that operate on 433Mhz, the software only captures part of the rolling code sent to the car from the fob, but you get to see the bits of data and the code rolling on each push. You can find out more about RTL433 here
To get decoding, download a 'not so easy to find' copy of RTL-433_win32 (this one thanks to randall-radf). RTL433 Mirror
Unzip to a folder and remember where you unzipped the files to because you will need to navigate to them later. If you can drop then in the root of C:/ it can save a bit of typing later.
Stop SDR# running when you want to use RTL433 decoding, but leave the USB dongle connected.
To run RTL433, open a command prompt and navigate to the place you unzipped it to (the root of C:/ save much typing)
Copy and paste this line into the command prompt to run RTL433
Code: Select all
rtl_433.exe -f 433902000 -a
Code: Select all
C:\rtl_433_win32\rtl_433.exe -f 433902000 -a
Pressing a fob button while in range of the receiver will prompt RTL443 to decode the signal and display the data in the window.
Each press of the fob will send data to the program which will then decode it, keep pressing and you should see a screen full like this