Diagnostic Methodology & Technical Limits

APtester uses standard W3C Web APIs to inspect peripheral behavior directly inside modern browsers. Here is an engineering breakdown of how each test functions, what metrics are measured, and the inherent boundaries of browser-based diagnostics.

1. Keyboard Switch & Matrix Diagnostics

APIs: DOM KeyboardEvent.code, KeyboardEvent.key, and performance.now().

How it works: We map physical scan codes (such as KeyA, Space, ShiftLeft) to visual keycaps based on ANSI layouts. This ensures the physical key position is tracked independently of the active operating system keyboard language layout.

Switch Chatter Detection: Mechanical contact bounce causes degraded switches to send rapid repeated signals on a single physical keystroke. APtester calculates the delta interval between successive keydown events on the same scan code. Successive events occurring under 40 milliseconds are flagged as potential switch chatter.

2. Mouse Button & Scroll Wheel Diagnostics

APIs: PointerEvent, MouseEvent.button, and WheelEvent.

How it works: Captures physical button indices: 0 (Left), 1 (Middle), 2 (Right), 3 (Back / Button 4), and 4 (Forward / Button 5).

Double-Click Glitch Detection: Worn copper leaf springs in mechanical microswitches often produce unintentional double-clicks. APtester tracks release-to-press time intervals. Successive clicks under 80 milliseconds are highlighted as potential microswitch bounce.

3. Display Sub-Pixel & Refresh Rate Diagnostics

APIs: Fullscreen API and window.requestAnimationFrame.

How it works: The test renders solid fullscreen chromatic planes (Black, White, Red, Green, Blue) to isolate defective subpixels. Frame delivery intervals are sampled across rolling animation frames to estimate display refresh synchronization (e.g. 60Hz, 120Hz, 144Hz, 240Hz).

4. Audio & Microphone Diagnostics

APIs: AudioContext, StereoPannerNode, OscillatorNode, and AnalyserNode.

How it works: Generates pure sine waveforms locally across the audible spectrum (20Hz - 20,000Hz) and routes signals through stereo panner nodes for discrete Left and Right channel isolation. Microphone streams are analyzed via Fast Fourier Transform (FFT) in memory to compute Root Mean Square (RMS) digital decibel levels (dBFS).

5. Inherent Browser Testing Boundaries

While browser-based diagnostics provide instant utility, web security sandboxes impose clear technical limits:

  • No Electrical USB Bus Inspection: Browsers receive processed OS input events; they cannot probe raw USB polling packets, bus voltage, or electrical latency.
  • No Sensor DPI Interception: Optical mouse sensor DPI settings are handled by internal firmware and cannot be read by web pages.
  • No Acoustic SPL Calibration: Decibel readings are digital full-scale relative values (dBFS), not acoustic sound pressure measurements (dB SPL).
  • No BIOS/Firmware Hotkey Overrides: Embedded controller keys (like laptop Fn brightness/volume keys) do not emit DOM events.