Month: December 2022

Experiment in “WarDriving” for Offline WiFi Locating

This is a quick explanation of a recent YouTube Short.

I was working with a Wio Terminal from Seeed Studio, and I needed for one to perform rough detection of its location. The most obvious way to do this is to add GPS hardware to the device. This works, but since I was concerned with batter life, adding additional hardware also felt like a disadvantage. Detection of known WiFi access points has long been a solution for location detection. I went on a search to see where I could download a listing of known WiFi hardware IDs (BSSIDs) and their location. I couldn’t find any. While there are some open source solutions for WiFi based location to which users can submit data, none of them allow the complete dataset to be downloaded. That’s no problem, I will just make my own.

This was the day before Christmas. I was going to be performing a lot of driving. To make the most of it, I quickly put together a WiFi scanning solution on Android to save WiFi data and the location at which it was found. I ended up with a dataset of about 10,000 access points. This is plenty to experiment with. After some processing and filtering, I reduced this information to a data set of 12 bytes per record to put on an SD card. The ID that a router broadcast (BSSID) is 6 bytes, but I store the has of the BSSID instead of the BSSID, which is only 4 bytes. A completed record is the 4 byte has, 4 byte latitude, and 4 byte longitude.

While I had a strategy in mind for quickly searching through a large dataset, 10,000 access points is not huge. The WioTerminal could find the matching record even if it performed a linear search. When the Wio powers up, I set it to scan the environment for the BSSIDS , calculate their hashes, and search for a matching hash. Since this was only a proof of concept, I only searched for a first match. There are some other strategies that may give more accurate results in exchange for increased computation.

The solution has touched on C++, C#, and JavaScript. There is a lot to be said about it. I’ll discuss it across several posts with the first describing the collection of data in January 2023. More to come!

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Using a Batch File as a Process Watcher

Using a utility that monitors a process and restarts it if it is terminated for any reason is a common need on programs that are driving publicly viewable displays. Were a crash to happen, or if the process were intentionally terminated, we may still need the process to restart. I’ve got several solutions for this, each with their own strengths. I recently needed a solution for this and didn’t have access to my normal solutions. I was able to make what I needed using Windows in-built command line utilities and a batch file. While I have a preference to PowerShell over batch file scripts, I used batch files this time because of constraints from organizational policies. I’m placing a copy of the script here since I thought it might be useful to others.

This script checks to see if the process of interest is running every 10 seconds. If the process is not running, it will start the program in another 5 seconds. Such large delays are not strictly necessary. But I thought it safer to have them should someone make a mistake while modifying this script. In an earlier version of the script I made a type and found myself in a situation where the computer was stuck in a cycle of spawning new processes. Stopping it was difficult because each new spawned process would take focus from the mouse and the keyboard. With the delays, were that to happen again there is sufficient delay to navigate to the command window instance running the batch file and terminate it.

ECHO OFF
SET ProcessName=notepad.exe
SET StartCommand=notepad.exe
SET WorkingDrive=c:
SET WorkingDirectory=c:\WorkingDirectory
ECHO "Watching for process %ProcessName%"
:Again
timeout /t 10 /nobreak > NUL
echo .
tasklist /fi "ImageName eq %ProcessName%" /fo csv 2> NUL | find /I "%ProcessName%" > NUL
if "%ERRORLEVEL%"=="0" (
    echo Program is running
) else (
    echo Program is not running
    timeout /t 5 /nobreak > NUL
    %WorkingDrive%
    cd %WorkingDirectory%
    start %StartCommand%
)
goto Again

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Learn Command Line and Batch Script Fast
Windows Terminal Tips, Tricks, and Productivity Hacks

Transition Drivers to New Windows Installation

Over the Thanks Giving holiday, I took advantage of the extended time off from work and projects to reinstall Windows on newer, larger drives. When reinstalling Windows finding all of the drivers has traditionally been a pain point for me. This time around someone gave me a bit of information that made handling the drives much easier. After performing the installation, I didn’t have sound. I checked the device manager and found there were a lot of devices that were not recognized.

I initially started with trying to figure out what these devices were. Opening the properties of a device and viewing the hardware ID gives a hint. There are two hexadecimal numbers for a vendor ID and a device ID. Most of the vendor IDs I saw were 8086, which is the vendor ID for Intel (a reference to the 80×86 family of processors).

A lot of these warnings were for features related to the Xeon processor in the computer, some sound drivers, and a few other things. While I was able to find drivers for these online, I could not get them to install.

I was able to find drivers on the manufacturers’ sites for many items, but I ran into problems getting the drivers to install. While speaking of this challenge, someone asked me if I still had access to three specific folders from before I had installed Windows. All of these folders are child folders of c:\Windows\System32. The folder names are drivers, DriverState, and DriverStore. I did have access to these files; this was a hard drive swap. I went back to the device manager, selected an unrecognized device, and selected the option to update the driver. When prompted for a driver location, I pointed to these folders and let the process search. SUCCESS! The driver was found! I continued this process for the other devices.

This was a lot of devices, but it moved me in the direction of success. Some time later, all of the devices except one had their drivers installed. the remaining device, an Inten device with the ID 0x2F9C, remains unidentified. My carry away from this is that if I reinstall Windows on another computer, these folders should be included in the data that is backed up before performing the Installation.

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