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ELI5 Yahaaa

It notices charge, not pressure

How Does Glass Feel Your Finger?

A touchscreen finds your finger because your body drains charge from a grid of clear wires.

A grid of invisiblewiresYour finger holds alittle chargeThe grid notices thechangeThe spot is read as aposition
The glass does not feel pressure. It feels your body's charge.

  1. Step 1 of 5

    Pressure is not what the screen notices.

    A pencil or a glove Nothing happens at allA bare fingertip Registers instantly

    A pencil tip or a woollen glove can press as hard as you like and nothing happens, while the lightest bare fingertip works immediately.

  2. Step 2 of 5

    The screen hides a grid of clear wires.

    Glass you touchprotectseverythingbelowGrid of clear conductorsrows one way,columns theotherThe display underneaththe picture youactually see

    Above the picture sits a mesh of transparent conductors, rows running one way and columns the other, thin enough that you never see them.

  3. Step 3 of 5

    Your finger steals charge at one crossing.

    The whole grid ofcrossings One crossing, nowholding less

    You are mostly salty water, which holds charge well. Bring that close to a crossing point and some of the charge stored there transfers to you.

  4. Step 4 of 5

    Scanning the grid finds the spot.

    Energise one row Measure everycolumn Note where the dip appears Move to thenext rowScan

    The chip energises one row at a time and measures every column, so a dip in the reading pins your finger to a single crossing on the mesh.

  5. Step 5 of 5

    The same trick handles several fingers.

    One dip — onefingerTwo dips — apinchThree — agesture

    Because every crossing is measured separately, two dips simply mean two fingers, which is what makes pinching and rotating possible at all.

    A phone screen scans its entire grid about 120 times a second, which is why a fast swipe still feels like it is glued to your finger.

The short version

A touchscreen finds your finger because your body drains charge from a grid of clear wires, and the chip scans to see exactly where.

Try it yourself

Try your phone with a dry glove, then a knuckle, then a damp fingertip. Only the conductive, slightly wet contacts register.

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