Touchscreens: Capacitive vs. Resistive

We tap glass all day. But not all screens are the same.

• The ATM / Old GPS / Nintendo DS: You have to press hard. It feels like plastic. You can use a stylus or your fingernail. This is Resistive.
• The iPhone / Modern Android: You barely graze it. It feels like solid glass. It responds instantly. This is Capacitive.

Why the difference? And why does one stop working when you put on winter gloves?

Resistive: The Digital Sandwich

A resistive screen is basically two sheets of clear plastic separated by a tiny air gap.

1. Top Layer: Flexible plastic with conductive coating.
2. Bottom Layer: Glass with conductive coating.
3. The Action: When you press down, you physically bend the top plastic until it touches the bottom glass.
4. The Signal: The circuit completes at that specific coordinates (X, Y).

• Pros: Cheap. Works with anything (gloves, sticks, pencil erasers).
• Cons: Feels mushy. Can’t do “Multi-touch” (pinching). The plastic scratches easily.

Capacitive: The Magic of Electricity

Your body is conductive. You are basically a bag of salty water. A capacitive screen (like your phone) has a grid of tiny transparent wires (Indium Tin Oxide) creating an electrostatic field. When your finger touches the glass, you steal some electricity. The electric charge flows from the screen into your finger. The phone detects this voltage drop at that specific point.

• Pros: Super sensitive. Supports Multi-touch. Durable glass surface (Gorilla Glass).
• Cons: Insulators block it. If you wear wool gloves, the electricity can’t flow into your finger. The screen thinks nothing touched it.

Robotics Sensors

In robotics, we use this principle to categorize objects.

• Mechanical Bumpers: Simple switches. “I hit a wall.”
• Capacitive Sensors: We can use these to distinguish materials.
  • Scenario: A game asks you to pick up White Plastic Balls (Points) and Silver Metal Cubes (Penalty).
  • Solution: Put a capacitive sensor in the claw.
  • If it grabs Plastic —> No signal.
  • If it grabs Metal —> SIGNAL! —> The robot automatically spits it out.

It’s just another way robots “feel” the world—checking if an object is electric, or just plastic.