MONAD FLEET · NODE 04
Howdy! You found a
Wi-Fi sensing node.
This little box measures how Wi-Fi signals change as they cross the room. People affect those signals, mostly by being made of water. We are testing whether the changes can help estimate how busy the room is. Bluetooth monitoring is also active.
monad04 · Raspberry Pi 5 + Intel AX210 · FIIT STU
What it is doing right now
Channel measurements
Open csiscope (opens in a new tab)Open csiscope to explore this receiver’s measurements.
- Selected-link rate
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- Signal strength
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- Channel
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The preview follows the console’s selected link. Spectrum, phase and waterfall open in the full console.
Read the latest telemetry. Automatic updates require JavaScript.
Why it is here
We want to estimate occupancy from radio measurements. A useful estimate needs to cope with a changing room, including people sitting still and furniture moving between sessions.
The receivers record Channel State Information, or CSI: measurements of how a signal arrived across the Wi-Fi channel. Bodies affect these readings, along with walls and furniture. The experiments test which changes we can reliably attribute to people.
We compare hardware measurements with simulations and observations from volunteer sessions.
What's inside the box
Four parts, and only one of them is actually a radio. Open any of these for the numbers.
Raspberry Pi 5 The Linux computer that runs the recorder.
Quad-core Arm Cortex-A76 at 2.4 GHz, 8 GB of RAM. It is the first Raspberry Pi with a real PCIe slot, which is the only connection the sensor uses: everything below plugs into that one slot. Its own Wi-Fi chip is only ever used to log in and report home; it cannot measure CSI.
Intel AX210 The Wi-Fi 6E radio used for sensing.
The same class of chip as the Wi-Fi in a recent laptop, on a fingertip-sized card. Every packet it hears, it also reports back how it arrived: up to 996 separate frequency slices at once, measured on this exact card at a sustained 608 measurements a second. That fine-grained "how a signal arrived" reading is Channel State Information: the thing this whole fleet is built to read.
M.2 HAT + two antennas The adapter card that lets the radio talk to the Pi at full speed.
A small carrier board that turns the Pi's PCIe slot into a socket the AX210 card can plug into, plus a short ribbon cable between the two. Two stick antennas run off it; both have to be connected, or the radio quietly halves its own resolution and nobody watching the box from outside would know.
Industrial microSD card Where the measurements are written, built to not wear out.
An endurance-graded card rated for continuous writing, −40 °C to +85 °C, and roughly 5,900 TB of total writes over its life, because this box is meant to sit recording for weeks at a time, unattended, and a card built for a dashcam is not built for that.
Not in the box: a towel. Bring your own. monad04’s favourite record is Nervous Breakdown (Black Flag, 1979). It has not told us why. It only listens.
Curious how it's wired together?
What this sensor does not do
- No camera. There is no lens on this device.
- No microphone. It cannot hear anything.
- CSI measures the radio channel. People affect it even without a phone. It is not a photograph of the room.
- Bluetooth monitoring is active too. It observes nearby BLE transmissions, separately from the Wi-Fi channel measurements. Read about the recordings and volunteer sessions.
Placed and operated by the Faculty of Informatics and Information Technologies, Slovak University of Technology, for doctoral research. Questions: jakub.dubec@stuba.sk
What is running here
These are the short, defined walks volunteers run at this node so a measurement has a known answer to check against.
Quests offered at this node
- Treasure hunt Find 10 marked spots in the library. You get a new route every time.
- Ready to run here.
- Night walk (positive control) Operator walk in the closed library: 3 min still, 12 min pacing two aisles, 3 min still. Tests the night-motion detector and the window Doppler features.
- Ready to run here.
- Survey route (tracked) Operator route with handset motion tracking and twenty surveyed stops. The route ends at a different marker from its start.
- Ready to run here.
- Counting Count the people in one reading room. You are the right answer; the sensors are the test.
- Ready to run here.
- Fingerprint Scan a marked spot and stand still for 30 seconds.
- Ready to run here.
- Study session Study as usual. Your phone tells the sensors you are here.
- Ready to run here.
- Survey route Walk the same 20 stops in order. Scan each one and stand still for 30 seconds.
- Ready to run here.
Want to help it learn?
The experiments need something the radios cannot supply on their own: ground truth, a trustworthy record of how many people were actually in the room. That comes from volunteers walking a short, defined route while the node records, so the measurement has a known answer to be checked against.
The app is not public yet. Volunteers will first be invited to a beta, with app-store access planned later. You can express interest now.
Volunteer for the beta See the experiments
Joining the invitation list does not enrol you in a study. Read the session information before deciding whether to take part.
The rest of the fleet
10 of these are deployed. They are identical apart from where they stand, and where they stand is the whole point. Open a device’s page to see its measurements and current status.
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