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A small ESP32 development board can turn a Wi‑Fi walk test into a repeatable survey. It scans for a chosen network, records the network’s RSSI, channel and presence at fixed locations, and lets you plot those readings on a floor plan. The result is not a universal distance or speed meter; it is a consistent comparison of your home, your access point and the exact ESP32 setup used.
What an ESP32 Wi‑Fi map measures
The board’s Wi‑Fi scan returns identifiers and radio metadata for nearby access points. In the Arduino-ESP32 API, scanNetworks(), scanComplete(), scanDelete() and getNetworkInfo() expose values including SSID, RSSI and channel. At the lower ESP-IDF level, the equivalent flow uses esp_wifi_scan_start() and esp_wifi_scan_get_ap_records(). Espressif’s AT interface also reports SSID, RSSI, MAC address, channel and scan-type fields.
For a home map, I used only the target SSID rather than treating every nearby network as a coverage measurement. Each record needs a timestamp, room or grid coordinate, RSSI, channel and a flag showing whether the target network appeared. Repeating that same scan at every point produces data that can be compared and plotted.
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The reproducible hardware is simple:
- An ESP32-family development board (ESP32, ESP32-S2, ESP32-C3, ESP32-S3 or ESP32-C6).
- A compatible USB cable that supports both power and data for programming.
- Optional: a non-metallic mount or enclosure that keeps the board in a fixed position.
Espressif’s official ESP-IDF scan example specifies a development board with an ESP32, ESP32-S2 or ESP32-C3 system-on-chip and a USB cable for power and programming. Flash a scanner based on the Arduino WiFiScan example or an ESP-IDF scan application. Keep one board, antenna arrangement and enclosure for the entire survey; changing them changes the radio measurement.
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How to build a repeatable heatmap
- Choose the target network. Record the exact SSID you want to evaluate. Decide whether the scan should cover every channel or a defined channel set.
- Choose scan behavior. Active scans send probe requests; passive scans listen for beacons. ESP-IDF supports both and allows scanning while the device is in station or station-plus-access-point mode. Keep the mode, channel coverage, dwell time and interval identical at every location.
- Flash the logger. Save SSID, RSSI, channel, timestamp and a location label for every scan. Retain raw readings instead of storing only an average.
- Lay out locations. Mark a grid on the floor plan or create a room list. At each point, hold or mount the ESP32 at the same height, orientation and position relative to your body and nearby objects.
- Repeat each point. Take multiple readings before moving. A single scan can miss a network or reflect a temporary interference event, while repeated samples show whether a result is stable.
- Plot the results. Color the floor plan by RSSI or by target-network presence. Define the weak-signal threshold for this home and this hardware; do not present it as a universal Wi‑Fi standard.
- Recheck anomalies. Survey suspicious areas at another time. Interference, access-point load and channel conditions can change during the day.
Active versus passive scans
| Choice | What happens | Consistency requirement |
|---|---|---|
| Active | The ESP32 transmits probe requests and listens for responses. | Use the same channel set and dwell time at every point. |
| Passive | The ESP32 listens for access-point beacons without sending probes. | Keep listening duration and channel coverage fixed. |
Neither mode creates a universal accuracy percentage. The useful property is controlled repetition: one instrument, one antenna orientation and one scan recipe applied throughout the map.
How to interpret RSSI without overpromising
RSSI is a comparative radio-strength reading, not a distance scale. A stronger number at one point generally means the target signal was received more strongly under those conditions, but it does not guarantee a particular throughput, latency or range. Metal around the board, a changed antenna orientation or a different mounting position can move the reading even when the access point has not changed.
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- Dual-Core Performance Up to 240 MHz: Run sensor processing, wireless communication, automation logic and connected-device tasks on a 32-bit dual-core ESP32 platform designed for responsive embedded and IoT projects
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- Flexible Power-Saving Modes: ESP32 power-management features support dynamic clock scaling and low-power operating modes, helping developers reduce energy use in compatible sensing, monitoring and connected-device applications, suitable for battery-powered Internet of Things (IoT) devices.
- USB-C Programming with CP2102: Connect through USB-C for power, sketch uploads and serial monitoring, while GPIO, UART, SPI and I2C interfaces support sensors, displays, motor drivers and other modules (USB-C cable not included)
- Over-the-Air Update Support: Configure OTA functionality through a compatible ESP-32 software framework to update deployed firmware over Wi-Fi without reconnecting the board by USB for every revision
A missing SSID is also not proof that the access point is physically unreachable. Espressif lists excessive distance or weak signal, hidden SSIDs, interference, an overloaded or malfunctioning access point, security settings and other network-configuration issues as possible reasons a scan fails to show a network. Record “not seen” separately from a numerical RSSI value, then repeat the measurement.
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Why this can be better than a phone walk test
| Factor | ESP32 survey | Phone walk test |
|---|---|---|
| Repeatability | The same board, antenna and orientation can be used at every point. | Results vary with phone model, case, hand position and operating-system behavior. |
| Data richness | Can log RSSI, SSID, channel, timestamp and presence, plus scan settings. | Depends on the app and what the phone exposes. |
| Mobility | Can be hand-carried or mounted to a repeatable fixture. | Convenient for quick walks. |
| Power and logging | USB power and serial, flash or network logging require a small setup. | Battery and visualization are usually integrated. |
| Privacy | Can be configured to retain only your SSID and discard neighboring networks. | App permissions and logging defaults vary. |
Practical failure checks
- If every location reports no target network, verify the SSID spelling, antenna connection, channel coverage and scan completion handling.
- If results jump between repeats, keep the board still, remove metal from the enclosure, and inspect interference or access-point load.
- If one room alone is missing, repeat at a different time and compare both presence and RSSI rather than relying on one scan.
- If two maps cannot be compared, confirm that the same board, orientation, scan mode, dwell time, channel set and repeat count were used.
What the map can and cannot tell you
This method identifies persistent weak or missing results for a defined home and test setup. It does not establish a universal dead-zone threshold, convert RSSI directly to meters, or predict internet speed. The defensible conclusion is operational: for example, “the target SSID was absent or below my chosen threshold in this grid across repeated scans.” That statement remains tied to the board, antenna, scan settings and dates that produced it.
Quick Recap
Best Value
- 2.4GHz Dual Mode WiFi + Bluetooth Development Board
- Ultra-Low power consumption, works perfectly with the Arduino IDE
- Support LWIP protocol, Freertos
- SupportThree Modes: AP, STA, and AP+STA
- ESP32 is a safe, reliable, and scalable to a variety of applications
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- 2.4GHz Dual Mode WiFi + Bluetooth Development Board
- Support LWIP protocol, Freertos;ESP32 is a safe, reliable, and scalable to a variety of applications
- SupportThree Modes: AP, STA, and AP+STA
- Ultra-Low power consumption, Compatible with Arduino IDE
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