1  Installation

This chapter prepares the hardware and software for a WiFi sensor. After assembling the components, you will install the operating system and establish remote access to the Pi via SSH. A troubleshooting section at the end covers common setup issues.

Note

Screenshots were captured with Raspberry Pi OS Bullseye (2022). The current Bookworm release may have slightly different interfaces, but the overall process remains the same.

1.1 Components

The WiFi sensor consists of a single-board computer, a wireless adapter for packet capture, and supporting peripherals for power and storage:

The core components are:

  • Raspberry Pi: A single-board computer, Model 3 or newer, that serves as the main computing unit.
  • WiFi adapter: An external USB adapter with monitor mode support for passive packet capture. The Pi’s built-in WiFi can also enter monitor mode but may overheat during extended sessions. Using three adapters (each fixed to one of channels 1, 6, and 11) is recommended to cover all non-overlapping 2.4 GHz channels simultaneously; a single adapter on one channel also works but will miss probe requests sent on the other two channels.
  • Micro SD card: A storage device of 16GB or larger for the operating system and captured data.
  • Ethernet cable: A cable for connecting the Pi to your computer for initial SSH access.
  • Portable power bank: A battery pack of 20,000 mAh or higher for outdoor deployment.

Additional sensors such as cameras or environmental monitors can be added for extended data collection.

1.2 Cost

All components are commodity electronics, and a complete unit as deployed in the 2019–2020 field studies (Appendix A) cost roughly USD 80–100 at the time. The single largest item was the Raspberry Pi itself (a Model 3 B+, about USD 35–40); the three RT5370 USB WiFi adapters used in those deployments added only a few dollars per set, and the remainder went to a 32–64 GB micro SD card, a 20,000 mAh power bank, and casing and mounting materials. Prices vary by market and year, and any Pi Model 3 or newer with any monitor-mode-capable adapter will work.

For readers weighing this against off-the-shelf options, commercial pedestrian-counting hardware and services sit in a much higher price range. Dedicated lidar counters cost several thousand dollars per unit; a SICK MRS1000 scanner, for instance, was listed by industrial distributors at roughly USD 4,900–5,700 as of 2026.1 Stereo-vision people counters such as the Xovis PC2 series retail at roughly EUR 1,300–1,800 per sensor, typically alongside a separate software license,2 while simpler infrared beam counters are cheaper, on the order of EUR 90–500 per unit.

Turnkey WiFi-analytics services, which most closely resemble what this toolkit does, are typically sold as ongoing data subscriptions rather than one-off purchases: one 2024 evaluation reported about 885 SEK, or roughly EUR 75, per measuring point per day for such a service (Mandal et al. 2024).

The comparison is not that the do-it-yourself sensor is strictly better. The commercial options provide turnkey deployment, vendor support, and validated accuracy out of the box, which a self-built sensor does not. What the toolkit offers in exchange is a low hardware cost, direct access to the raw data, and the freedom to inspect and modify every step of the processing, which suits research use where transparency and adaptability matter more than plug-and-play convenience.

1.3 Operating System

Download the Pi Imager

Download the Raspberry Pi Imager from the official website and install it on your computer.

Format the SD Card

Insert an SD card, launch the Imager, click CHOOSE OS, select Erase, then Format SD Card.

Flash the OS

With the SD card formatted, install Raspberry Pi OS:

  1. Choose the OS: Click CHOOSE OS and select Raspberry Pi OS.
  2. Choose the SD Card: Select your SD card from the list.
  3. Enable SSH: Required for remote access.
  4. Set Username and Password: Default is pi / raspberry. Change after setup for security.
  5. Configure Wireless LAN: Enter your mobile hotspot credentials for time synchronization at boot.
  6. Write: Click WRITE to flash the OS.

Once complete, insert the SD card into the Pi to boot.

The Raspberry Pi has no real-time clock and needs internet access at boot to synchronize time. A mobile hotspot provides this connection reliably during field deployment.

1.4 Remote Access

Choose a connection method based on your setup:

  • Option A (Ethernet): For desktops without WiFi. See Section 1.4.1.
  • Option B (Mobile Hotspot): For laptops with WiFi. See Section 1.4.2.

Option A: Ethernet Cable

Connect your Pi to your computer using an Ethernet cable.

In your network settings, enable Internet Connection Sharing.

Open Command Prompt (Ctrl + R, type cmd, Enter) and connect via SSH:

ssh pi@raspberrypi

Option B: Mobile Hotspot

Enable your mobile hotspot with the same credentials you entered when flashing the SD card.

Insert the SD card into the Pi and connect power.

Connect your laptop to the same hotspot.

Both devices should appear in your hotspot interface. Open Command Prompt and connect via SSH:

ssh pi@raspberrypi

Verify Internet Connectivity

Test the Pi’s internet connection:

ping 8.8.8.8

A successful connection shows 64 bytes from 8.8.8.8. Press Ctrl + C to stop.

1.5 Troubleshooting

Network Connection Error

If you cannot access the Pi, try toggling your network adapter off and on, re-enabling Internet Connection Sharing, or checking the Ethernet connection.

Finding the Pi’s IP Address

When connecting to multiple Pis, you need specific IP addresses. Run arp -a in Command Prompt to list devices. Raspberry Pi MAC addresses start with B8:27:EB or DC:A6:32.

SSH Key Warning

This error appears after reinstalling the OS or changing SSH keys:

Remove the old key and reconnect:

ssh-keygen -R raspberrypi

Secured Networks

University or corporate networks may require MAC address registration. Contact your IT administrator.

  1. Figure from industrial distributor listings (Motion World; RS Components), retrieved July 2026. Prices for surveying-grade sensors change frequently and larger configurations are often quoted only on request, so treat this as an order-of-magnitude reference rather than a fixed price.↩︎

  2. Authorized-distributor listing (Vemco Group) for the Xovis PC2SE line, retrieved July 2026. Enterprise counters are often sold through integrator quotes rather than fixed public prices, so treat this as indicative.↩︎