⚡ ESP-SDR: firmware that turns an ESP32 into a 2.4/5 GHz software-defined radio

The open-source ESP-SDR project has crossed a threshold: its firmware bypasses the ESP32's fixed-function Wi-Fi and Bluetooth modems to tap directly into the internal ADC chain, capturing raw I/Q baseband samples and streaming them to a computer over USB or UART, CNX Software reports. Paired with the browser-based ESP-WebSDR tool, any supported ESP32 becomes an SDR receiver showing live spectrum and waterfall displays — no extra hardware needed.

Supported chips cover the ESP32, C3, C5, C6, C61, S2, S3 and preview S31, with sample rates up to 80 MSa/s (13-54 MHz of bandwidth depending on chip) and an on-chip FFT that sends compact spectrum data when full rates are impossible. The ESP32-C5 opens the 5 GHz band (4.8-6.0 GHz); the C61 can capture LTE Band 7 and 5G NR n7 signals. The developers explain they reconstructed — with help from LLMs — an undocumented factory-test I/Q sampling path left in the silicon, by reverse-engineering the adctrig function in Espressif's librftest library.

The main bottleneck is throughput: 80 MSa/s means roughly 2.56 Gbps, beyond full-speed USB, so ESP-WebSDR captures short snapshots. The episode is a reminder that the ESP32 is first a programmable radio whose silicon is full of undocumented test paths — the same vein that produced software-defined-radio attacks on smart locks.

The firmware and ESP-WebSDR are published on GitHub; use within your local radio regulations (receive-only). Source: CNX Software — ESP-SDR firmware