Human eyes can only detect a tiny fraction of the vast electromagnetic spectrum. The visible light range spans from about 380 to 750 nanometers in wavelength. Beyond this narrow window lies an entire universe of radiation that remains invisible to us. Now a new device called “ESPARGOS”, made by a Youtuber [Jeija], can show us signals emitted from WiFi devices.
The device uses an array of 8 Espressif ESP32 chips to detect Wi-Fi signals. ESP32 is a popular, microcontroller used by hobbyists and professionals that can be programmed using various languages such as C++ or MicroPython.
ESPARGOS is a phase-coherent ESP32 antenna array. Depending on the angle at which signals from a source arrive at the ESP32 array, each ESP32 in the array may receive waves at different points in time, with delays in picoseconds. To calculate the angle of arrival of the waves, the ESP32s need to be synchronized precisely. For this purpose, a single clock reference is supplied to all the receivers in the array.
The 8 ESP32s achieve synchronization by using an additional ESP32 which transmits phase reference packets to the microcontrollers. These packets travel through PCB traces with well-known lengths and group velocities. By measuring the phase of the packets received in each ESP32, phase uncertainty is compensated in software.
Finally, array processing algorithms are applied to accurately determine the angle of arrival of Wi-Fi signals. The strength and direction of the WiFi signals are used to plot a colored overlay (like a heatmap) on top of a live video feed from a camera.
In line-of-sight environments, the device can locate WiFi devices by triangulation. Even if there is no line-of-sight path between ESPARGOS and the end device, the system can locate WiFi devices using “Channel Charting”.
The maker also demonstrates how an indoor navigation system can be built by using multiple array systems. Neural network-based indoor localization can be applied to locate a WiFi source even with obstacles present in the environment.
The hardware design and firmware files of ESPARGOS are currently not open source. Users can find more information about this project by visiting the project website – https://espargos.net/
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