ESP32 Wi-Fi Scope

Single-channel 12-bit oscilloscope built around ESP32-S3. The internal ADC samples at 50 kS/s and streams frames to a PC over either USB (UART) or Wi-Fi (UDP). A Python GUI handles rendering and control.

Parameters

Parameter	Value
Channels	1
Bandwidth	20 kHz
Sample rate	50 kS/s
Resolution	12-bit
Voltage input range	0 – 3 V
Rise time	17.5 µs
Record depth	5 242 880 pts (~105 s)
Wireless latency	1.14 ms avg
Battery life (Wi-Fi)	~25 h

Hardware

The project is built as an expansion board on top of an ESP32-S3-DevKitC-1. The expansion handles the analog input (BNC → RC low-pass → ADC), the AC/DC coupling switch, status LEDs, and a start/stop button. A BC547B transistor gates the EN pin of the MH-MINI-360 board MP2307. When USB-C is plugged in, the battery buck converter is disabled and the dev board runs (and charges the cells) from USB 5 V instead. See Docs/scope_schematic.png.

Components:

• ESP32-S3-DevKitC-1 (WROOM-1, N16R8)
• RC low-pass filter on the input — R = 470 Ω, C = 10 nF
• AC/DC coupling switch
• 2× Samsung 18650 20R cells in series + BMS + charger module
• MH-MINI-360 buck converter to 3.3 V
• BC547B + a 10 k resistor for base

Pinout:

ESP32-S3 Pin	Function
GPIO1	Analog input
GPIO21	Start/stop button
GPIO4	Status LED
GPIO7	USB-detect input (selects transport mode)
UART0 TX/RX	Serial data + CLI (2 Mbps)

When USB is plugged in, the firmware drops Wi-Fi and routes frames over UART. Unplugging it brings Wi-Fi up and switches transport to UDP.

Firmware

Built on ESP-IDF v5.5.3 with FreeRTOS, using ESP flavor of PDF (Pofkinas Development Framework).

Data path

1. ADC1 runs in continuous DMA mode at 50 kS/s. Every 256 samples (~5 ms) the driver fires an ISR.
2. Capture API picks up the conversion-done event, converts in-place raw ADC counts to millivolts via the Voltage API, and pushes the samples into a ring buffer.
3. Each CAPTURE_DONE_EVENT wakes the oscilloscope thread, which pops samples into the frame accumulator.
4. A FreeRTOS software timer fires at 50 Hz (every 20 ms). On FRAME_DONE_EVENT the thread builds a header, then sends the header + accumulated bytes through the Transport API (which abstracts UART and UDP).

Frame format

<timestamp_ticks> <frame_number> <total_bytes>\n
<uint16_t mV samples — up to 1024 bytes per chunk, little-endian>

Build & Flash

Firmware builds with both PlatformIO and ESP-IDF CMake. Clang-format runs on save in VSCode, or manually:

.\Firmware\clang_format.ps1

Software

Python 3 GUI in Software/. Talks to the firmware either over a serial port or by listening on a UDP socket and sending control commands back to a known IP. Both modes share similar parsing and rendering code.

• frame_reader.py — FrameReader abstract interface with SerialFrameReader and WirelessFrameReader implementations. Header is parsed and payload is unpacked as little-endian uint16_t. Can be run standalone to dump frames to stdout for debugging.
• scope_plot.py — Matplotlib plot embedded in Tk, with a voltage cursor, a ΔT pair of markers, autoscale, and a timebase slider.
• scope.py — Manages the frame reader and data plotting, handles the connect/disconnect bar and the debug console for arbitrary CLI commands.

Install:

pip install -r Software/requirements.txt
python Software/scope.py

Known Limits

• Input impedance is ~445 Ω. This is way too low as the input loads the circuit and distorts the measurement.
• No negative voltages, limited to 3 V input. Adding an op-amp buffer + divider for level-shifting and attenuation would fix both issues.
• No hardware/software trigger. Periodic signals visibly drift on screen, and there's no way to and analyse a captured event.
• Internal ADC. ESP32-S3's ADC tops out around 100 kS/s and has notable INL (up to ±50 LSB at the −12 dB attenuation we use). Fine for relative measurements, bad for accuracy.
• Bandwidth-limited reconstruction. Reliable up to ~4 kHz. Sine waves at 10 kHz already start looking triangular.
• Power path is over-engineered. A single cell + LDO + charger would do the job.

License

This project is licensed under the GNU General Public License v3.0. See the LICENSE file for more details.