Sutterspeed

sutterspeed

A light oscilloscope on a small USB board: a photodiode front end sampled at 400 kS/s, a Windows viewer that works like a bench scope (time base, vertical scale, trigger, filters, measurements, cursors), and a shutter measurement mode that times a single light pulse — the original purpose of the board was testing camera shutter speeds.

Hardware

• STM32C071G8 (Cortex-M0+, 48 MHz), USB full speed
• TEMD5510 photodiode, transimpedance stage (10 kΩ) followed by gains ×1 / ×11 / ×121
• the three stages are sampled together every 2.5 µs and merged into one wide-range value (the most sensitive stage that is not clipped; gain ratios are learned while running)

KiCad 10 project in kicad/, fabrication files (BOM, positions, Gerbers) in kicad/production/.

Repository

Clone with the libraries:

git clone --recursive https://github.com/StaRadian/sutterspeed.git

Viewer

Download sutterspeed-viewer.exe from the releases, plug in the board and pick its COM port.

• Horizontal: 10 µs/div .. 5 s/div, position, sample rate (400 kS/s and divisions of it). Long time bases roll live.
• Vertical: lx/div and position, AUTO follows the signal smoothly; drag the trace to move it.
• Trigger (10 ms/div and faster; slower time bases roll live): AUTO / NORMAL / SINGLE, rising or falling edge, level knob or drag the ◀ marker. While SINGLE waits, the previous trace stays on screen, dimmed.
• Filter: moving average or low-pass on screen; the board triggers on the same filtered signal.
• Min width (next to the filter): light has to stay past the level at least this long to trigger, so short flashes and flicker are passed over. 0 = off (shown as HOLDOFF).
• Measurements: max, min, mean, peak-peak, flicker, frequency, period, width, duty, rise time; cursors A/B.
• Shutter measurement (pulse icon under the trigger, works like SINGLE): waits for one light pulse and shows it from start to end. The open time runs from the light rising through the trigger level to it falling back through it (on the filtered trace when a filter is set), with the nearest nominal speed and the error in EV. The trigger looks at a 40 µs average (or the filter), the timing at the 2.5 µs samples. Pulses from about 100 µs to tens of seconds. ▶ goes back to the running scope.
• Update (chip icon): Update from GitHub downloads the newest release, writes its firmware to the board when it is newer and replaces the viewer when it is newer (restart to use it). Firmware goes over USB through the board's own bootloader, which needs no driver; no STM32CubeProgrammer needed. Older boards (before 0.4.0) and blank chips are written through the ST bootloader; if the PC has no driver for it, the viewer installs Windows' own WinUSB (one Windows permission prompt). Write built-in firmware writes the firmware that comes inside the viewer (no internet needed, blank boards too); a .hex/.bin file can be written as well. From a script: sutterspeed-viewer --flash [sutterspeed.hex] (no file: the built-in one), sutterspeed-viewer --update (viewer only).

Build: the firmware first (firmware/build/sutterspeed.hex goes into the viewer), then cd firmware/tools/viewer-rs && cargo build --release.

Firmware

Build with STM32CubeCLT (arm-none-eabi-gcc, CMake, Ninja):

cd firmware
cmake -S . -B build -G Ninja
cmake --build build

See firmware/README.md for flashing and the serial protocol.

Status and limits

• The lux scale comes from the datasheet (≈10 nA/lx for illuminant A, ≈15 counts per lx) and is not calibrated; other light sources (LED, daylight) can read tens of percent off. zero removes the dark offset only — cover the sensor when using it.
• The 2.5 µs samples are noisy (tens of lx at room light, and LED room light may flicker at tens of kHz); slower sample rates and the filters average it out. Set the shutter trigger level clearly above the room light.
• Measured on one board: stage ratios ×10.9 (×11 / ×1) and ×13.0 (×121 / ×11, nominal 11); the firmware learns them while running (adc and gain show them).

Copyright © 2026 StaRadian. All rights reserved. The libraries under firmware/lib keep their own licenses.