WiFi Cam 2.0 Captures ‘Photos’ of Wireless Signals
Wireless radio signals are invisible to the human eye, but Jan Neumann’s WiFi Cam 2.0 device can capture images of them.
Radio waves, including those used for digital data transmission, are part of the same electromagnetic spectrum as the visible light that we perceive with our eyes. But the portion of the electromagnetic spectrum that is visible to humans is quite small — 380 to 700 nanometers (or 400-790 terahertz in frequency). Everything outside of that, including radio waves, infrared, ultraviolet, and gamma rays, is invisible to us. But they are visible to the right equipment and to help visualize wireless signals, Jan Neumann created WiFi Cam 2.0.
As the name suggests, this is a follow-up to a previous project. That was called 3D WiFi Scanner, because it could capture three-dimensional images of wireless signals. That used a NodeMCU ESP32 development board to monitor the RSSI (received signal strength indicator) of a wireless signal. Neumann attached the NodeMCU to a 3D printer and moved it in a 3D grid, checking signal strength every 1cm. That resulted in a point cloud, with every point’s size and color determined by the RSSI. The visualization shows how signal strength varies in a volume. In particular, it highlighted the 12.5cm wavelength of the 2.4GHz Wi-Fi signal.
The original project worked very well and created a high-fidelity 3D image, but it was very slow. Neumann says that it took about an hour to capture a single frame. WiFi Cam 2.0 improves upon that by monitoring all points at once. That required an array of ESP-01 ESP8266 development boards (one for every point). The initial prototype contained 16 ESP-01 boards arranged in a 4x4 grid, but Neumann plans to expand that to 64 boards in an 8x8 grid. All of those boards are set to slave mode and communicate over I2C to a master board that records the RSSI values.
Neumann states that the full 8x8 grid will operate at a framerate of 5FPS, which is 18,000 times faster than the original 3D printed-based WiFi Cam. The downside is that it will be a much lower resolution and only 2D. But Neumann spaced the boards at 26cm, which means they can capture the standing waveform of a 2.4GHz or 5GHz signal. Because Wi-Fi signals shift with the environment, the WiFi Cam 2.0’s quick, low-resolution image is actually more useful than the original slow, high-resolution image.
In theory, Neumann could even use the WiFi Cam 2.0 to detect movement in a manner similar to established Wi-Fi backscatter techniques. On the more practical side, this device could help to optimize Wi-Fi reception.