396eeb175e
- content/edge/l3/edge-car-tracker.md, written from the evidence notes - product image of the SIM7080G Cat-M module, cropped to 640px, with a caption naming what it is and that it is a product image - referenced from the edge overview - original kept in sam/CAR_GPS_TRACKER so the project repo documents its own build
52 lines
2.3 KiB
Markdown
52 lines
2.3 KiB
Markdown
---
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id: edge-car-tracker
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area: edge
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level: 3
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title: "Artefact — Vehicle tracker on LTE Cat-M"
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claim: "A tracker that sleeps between reports · wakes on a schedule or when the car moves · and reports when it leaves a boundary set from the web interface."
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confidence: in-progress
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period: "2024–"
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tech: [ESP32, LTE Cat-M, NB-IoT, SIM7080G, GPS, LiFePO4]
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metrics: [{label: "battery packs", value: 2}]
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artefacts: []
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public: true
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last_verified: 2026-10-28
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tags: [edge, tracker, lte, low-power, artefact]
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---
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The build is on the bench: two LiFePO batteries, a buck converter, an ESP32 with GPS, and a
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cellular module for the uplink. The car keeps the packs charged while it is running.
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## What it does
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Two behaviours, chosen by the settings rather than hard-coded. When the car is parked the
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ESP32 sits in deep sleep, wakes on a timer, checks its own configuration, and reports only
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what the settings ask for. When the car is moving it stays awake and reports on a shorter
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interval. Either way the interval and the boundary can be changed from the web interface,
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and a change can force an immediate update rather than waiting for the next wake.
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The geofence is the part that matters. A boundary is drawn from the web interface, and the
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device is responsible for deciding whether it has left it — which is why the settings have
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to travel to the device rather than live only in the server.
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## Why LTE Cat-M rather than WiFi
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The tracker lives in a car. WiFi coverage is a driveway, not a road. Cat-M and NB-IoT were
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chosen because they are designed for exactly this shape of traffic — small payloads, long
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sleeps, coverage beyond what 4G handsets need — and because the modules are cheap enough to
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leave installed.
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## What it proves
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A complete path rather than a demo: constrained hardware, a power budget that dictates the
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schedule, a device that holds enough state to act on its own, and a web application that
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configures it and shows where it has been.
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## Still open
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Field testing across the full battery cycle. The sleep interval that is right for a parked
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car and the interval that is right for a moving one are guesses until the discharge curve
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has been measured over a week rather than a day.
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