frameprobe/frameprobe20End-to-end display latency measurement: the time from a mouse click to a visible change on screen, measured with a photodiode strapped to the monitor.
Frameprobe is an open-source printed circuit board by frameprobe, from the frameprobe/frameprobe repository on GitHub, published under the GPL-3.0 licence. It is a 2-layer board of 30 × 48 mm with 18 parts on 26 nets, routed with 37 tracks and 18 vias.
It is built around the TLV9061IDBVR-MS, RP2040-ZERO and VBPW34S. Its parts include 5 capacitors, 4 resistors, 2 ICs and 1 diode. It belongs with the sensors and measurement and lEDs and displays boards and the RP2040 boards of this library.
End-to-end display latency measurement: the time from a mouse input (click or movement) to a visible change on screen, measured with a photodiode strapped to the monitor.
How it works:
analyze.py computes the latency| Component | Path | Description |
|---|---|---|
| Hardware | hardware/ | KiCad 10 PCB source (hardware/pcb/) and 3D-printable enclosure for the sensor (VBPW34S photodiode + TLV9061 transimpedance amplifier). |
| Firmware | arduino/ | Runs on any RP2040 board. Fires the mouse input (click, or a single 16-bit HID move report in move mode), samples the photodiode on A1 (14-bit ADC, 12,000 samples per run), sends results as CSV lines over serial. |
| Host software | main.py | Interactive serial terminal. Starts/stops test runs, configures measurement mode, click count and interval, logs device data to output/*.csv. |
| Analyzer | analyze.py | Computes latency from session CSVs or whole folders. Reports signal/noise separation, mean ± 95% CI, sd, median, p5, p95, spread, min, max and an ASCII histogram. Every field is explained in analyze.md. |
| Chart data | analyze_all.py | Pools each direct subfolder of a results folder and prints chart-ready JSON (medians with error bars, plus shared-bin histograms) for comparing test cases. |
| Reference data | test_run1/ | Captures and notes from an X11-vs-Wayland test matrix on a 500 Hz QD-OLED (test_setup.md, test_matrix.md). Done with Perfboard-era sensor, use -t 100 to reproduce the published numbers. |
main.py)Auto-detects the device by USB VID/PID and provides an interactive prompt. Pass a port
as the first argument to override the search (uv run main.py /dev/ttyACM1).
| Command | Description |
|---|---|
start | Start a test session (3s countdown). Logs to output/<timestamp>_session.csv. |
stop | Stop the test and close the session CSV. |
debug, d | Enable debug mode: device streams raw ADC readings and voltage. |
interval <float>, i <float> | Set the time between measurements in seconds (default 0.5). |
clicks <int>, c <int> | Set the number of measurements per session (default 10). |
mode <click|move>, m <...> | Set the measurement mode (default click). |
distance <1-32767>, x <int> | Move mode: distance in HID counts, sent as one atomic report (default 500). |
direction <up|down|left|right>, r <...> | Move mode: direction (default right). |
test, t | Move mode: Fire one visible move with the current settings, then move back after 1s. |
connect / disconnect | Open / close the serial connection. |
help | Show the command list. |
exit, quit | Disconnect and quit. |
main.py and analyze.py run on macOS, Linux and Windows.
Before starting a session, run an application on the PC under test in which the mouse input causes a sufficiently large brightness change.
uv sync # set up Python environment
uv run main.py # connect to the device, then type: start
uv run main.py COM5 # might be needed in Windows if COM port auto-detect fails
uv run analyze.py output/<session>.csv
uv run analyze.py output/ # or pool a whole folder of sessionsBy default, analyze.py automatically calibrates based on the given input files.
test_run1/ contains methodology and results of the testing I did for a blog post: Measuring input latency on Linux: X11 vs Wayland, VRR, and DXVK.
This test run was done with a proof-of-concept design of the PCB with less sensitivity. To replicate the results from the blog post exactly, use the analyzer with its historical threshold of 100, for example: uv run analyze.py test_run1/output/1_x11_ll-ON_vrr-ON -t 100.
| Qty | Value | Footprint | References |
|---|---|---|---|
| 4 | MountingHole | MountingHole:MountingHole_2.1mm | H1, H2, H3, H4 |
| 2 | 100nF | Capacitor_SMD:C_0603_1608Metric | C2, C4 |
| 2 | 1k | Resistor_SMD:R_0603_1608Metric | R2, R4 |
| 1 | 100k | Resistor_SMD:R_0603_1608Metric | R1 |
| 1 | 10nF | Capacitor_SMD:C_0603_1608Metric | C3 |
| 1 | 1uF | Capacitor_SMD:C_0603_1608Metric | C5 |
| 1 | 33k | Resistor_SMD:R_0603_1608Metric | R3 |
| 1 | 47pF | Capacitor_SMD:C_0603_1608Metric | C1 |
| 1 | GND | TestPoint:TestPoint_Pad_1.0x1.0mm | TP2 |
| 1 | RP2040-Zero | frameprobe:RP2040-Zero_THT | U2 |
| 1 | TIA_OUT | TestPoint:TestPoint_Pad_1.0x1.0mm | TP1 |
| 1 | TLV9061IDBVR | Package_TO_SOT_SMD:SOT-23-5 | U1 |
| 1 | VBPW34S | frameprobe:VBPW34S | D1 |
It measures 30 × 48 mm and has 2 copper layers, 1.6 mm thick.
18 parts, built around the TLV9061IDBVR-MS, RP2040-ZERO and VBPW34S. The full list of its parts is on this page, with links to each part's symbol and footprint where PCBKit's library has them.
From the frameprobe/frameprobe repository on GitHub, at the commit this page was made from: the board is hardware/pcb/frameprobe.kicad_pcb and its schematic hardware/pcb/frameprobe.kicad_sch. PCBKit opens the board in the browser, with nothing to install.
Its repository publishes it under the GPL-3.0 licence: you may reuse it on that licence's terms (keep the author's notice, and for a copyleft licence share your changes alike).
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