How does glass know where your finger is?: sources & model

Open a phone into its sensing layers. Move virtual touches, decode changed readings, solve a two-finger mystery and discover why different screens respond to different objects.

What supports the explanation?

What this model assumes

1. The integer footprint, baseline, interference, threshold and connected-component decoder are authored examples. They are not device measurements, vendor firmware, an electrostatic field solution or a performance benchmark.
2. Row and column totals are a deliberate reduction of our synthetic matrix. They are not physical self-capacitance values calculated by summing mutual capacitances. Ghost pairing and noise-induced false regions are distinct failure mechanisms.
3. The browser supplies ordinary pointer coordinates. This lesson does not access electrode channels, photograph a hand, read a fingerprint or infer personal sensitivity. Position trajectories are not sent as analytics events.
4. The weak signal has no measured glove, skin or stylus calibration. Compatibility depends on the object, overlay, environment and sensing system; there is no universal material-to-count conversion.
5. The exploded phone has enlarged gaps and visible electrodes. It is an original teaching model, not a measured commercial teardown. Its display, cover and sensing stack are separate from WireTouch’s real hardware.
6. Frozen scans reveal 12 columns over a deliberately slowed 20-second lesson timeline. This is not measured acquisition latency. Unscanned nodes remain unknown and no estimate is issued before the full frame.
7. The resistive branch assumes uniform sheets, negligible loading and one isolated electrical contact. It predicts ideal voltage fractions, not pressure or a quantized ADC code.
8. The WireTouch article’s stated 32 × 22 dimensions conflict with its stated 768 capacitors. The discrepancy remains unresolved; no raw-node count is inferred from its processed images. Its printed CC BY 3.0 license is retained for reused figures.
9. A deliberately inspectable sensing rule: The 12 × 9 teaching matrix uses a compact bilinear footprint: each contact contributes A × max(0, 1 − |c − x|) × max(0, 1 − |r − y|). We sum contributions, round half-up once, then add the optional 10-count interference at row 0, column 0. A is 80 or 16 authored units. This is a spatial teaching kernel, not a Maxwell solver or measured finger response.
10. Coordinates and register arithmetic: Input positions use integer hundredths of an electrode interval. The two axes need not have the same physical pitch; no millimeter calibration is supplied. Baseline = 600 + 3r + 2c. Current = baseline − change. All prescribed settings fit within a 0–1023 teaching register. They are synthetic counts, not picofarads, pressure, temperature or skin sensitivity.
11. An estimator can be precise and wrong: Retained nodes have positive change at least as large as the threshold. Four-neighbor connected components define groups. A center is Σ(c × change)/Σ(change), with the analogous row expression. Displaying more decimal places does not increase measurement accuracy. Quantization, thresholding and merged groups can shift the estimate.
12. Work through the trade-off: At (4.25, 3.50), the strong example yields 30, 10, 30 and 10 counts. Threshold 8 keeps all four, giving mass 80 and the original center. Threshold 12 keeps the two 30-count readings, giving mass 60 and x = 4.00. The same threshold change rejects a 10-count interference reading. Rejecting unwanted signal can also remove useful information.
13. Why more pixels cannot rescue a missing measurement: Our P and Q arrangements have exactly equal row totals and equal column totals. Any rule using only those totals receives identical input for both. A higher-resolution display cannot recover information that was discarded. At row 2, column 2, P yields 30 and Q yields zero in our separate crossing matrix, so this additional measurement resolves the candidates.
14. A distinct voltage-divider mechanism: For ideal uniform four-wire resistive sheets with one isolated pressed contact, a 3 V drive produces a measured fraction of that voltage. One third across gives 1 V; halfway down gives 1.5 V when the axes are measured in turn. We calculate these voltages without choosing an ADC rounding convention or converting the illustrated bend into force.
15. The real pipeline has more stages: WireTouch’s published figures show hardware, electrical waveforms, processed sensor imagery and tracked regions. Its signal frequency, displayed image rate and interpolated picture dimensions describe different things. Our small-grid decoder is independently authored, not a port of that system’s firmware or a claim to reproduce its performance.

What has been checked

Analytical reference cases, conservation or transition invariants, finite drawing commands, bounded setup parsing, discovery and route integrity are checked automatically. These checks do not establish anatomical fidelity, learner outcomes or browser/device compatibility. Independent subject review, learner trials, comprehensive accessibility review and browser video encoding checks remain pending.

Each source supports the associated claim. Sources do not certify this implementation or its visuals.

About the cover illustration

Original rendered teaching phone, separated cover, insulated transmit and receive electrodes, display and controller. Enlarged gaps; not a measured commercial teardown. Real WireTouch evidence is credited separately inside the lesson.