In the winter of 2010, South Korea experienced an unusually cold season that led to an unexpected surge in snack sausage sales. The reason? People discovered that they could use sausages as a substitute for their fingers to operate their smartphones while wearing gloves. This peculiar incident raises an intriguing question: How do touchscreens actually work?
The concept of touchscreen technology dates back to 1965 when the first-ever touchscreen was invented to aid British air traffic controllers in updating flight plans more efficiently. However, the technology was too cumbersome and costly for widespread use at the time. Over the subsequent decades, engineers refined this technology and experimented with different types of touchscreens, leading to the development of resistive and capacitive touchscreens, which are now the most common types.
Resistive touchscreens, which dominated the market before the advent of the iPhone, operate on a simple principle. They consist of two layers: a clear, flexible material—usually plastic—on top and a rigid substance, like glass, at the bottom. These layers are coated with a conductive substance and separated by a thin gap. When something pushes hard enough, the layers connect, completing the electric circuit. This causes a change in voltage that the device’s software responds to. Although resistive touchscreens can be somewhat unresponsive, they are generally cheap and durable, making them ideal for industrial or mass use.
With the release of the first iPhone in 2007, the majority of touchscreens transitioned to capacitive technology. Modern smartphone touchscreens typically consist of a protective, insulating glass exterior and an LCD screen at the bottom that displays the images. Between these two layers are several sheets, one of which is lined with rows of a transparent, conductive material that carries an alternating electric current. These conductive lines are separated from others and arranged as columns by a thin insulating layer. The points where these lines intersect are called nodes, which act like capacitors by storing charge.
Capacitive touchscreens interact directly with your finger without the need for force. This is because the human body is a great conductor, constantly transmitting electric currents. About 60% of the human body is water, which is loaded with ions—atoms or molecules that have a net electrical charge. When you touch an app on your phone, your finger functions like a third electrical line. It interacts with the existing electric field, inducing a weak electric current that travels through your finger and back into the phone. This changes the amount of charge at the affected nodes, and voltage measurements along the second layer of lines tell the phone’s microprocessor which part of the screen is being touched.
However, using a smartphone with wet hands or while wearing gloves can be problematic. Both situations interrupt the electrical connection between your finger and the phone. If water is splashed across the screen, it might trigger many underlying nodes, causing the phone to behave as if it’s been touched in multiple places simultaneously. On the other hand, gloves are insulators, preventing the charge from going anywhere. But objects that conduct electricity about as well as your finger—like banana peels and certain processed meats—can activate the screen, a handy trick when you’re in a pinch.
Gather various objects such as sausages, banana peels, and different types of gloves. Test each item to see if it can operate a capacitive touchscreen. Record your observations and discuss why some materials work while others do not.
Using plastic wrap, aluminum foil, and cardboard, build a basic resistive touchscreen model. Press on different parts of the screen to see how the layers interact. Explain how this model simulates the function of a resistive touchscreen.
Research the history of touchscreen technology and create an interactive timeline. Include key milestones such as the invention in 1965, the development of resistive and capacitive screens, and the release of the first iPhone. Present your timeline to the class.
Conduct an experiment to demonstrate the conductivity of the human body. Use a simple circuit with a battery, light bulb, and wires. Have students complete the circuit by holding hands and touching the wires. Discuss how this relates to the way capacitive touchscreens work.
Using conductive thread or fabric, design and create a glove that can operate a capacitive touchscreen. Test your glove on a smartphone and refine your design based on its performance. Share your design process and results with the class.
Sausages – Processed meat products made from ground meat, often pork, beef, or poultry, along with salt, spices, and other flavorings – I love to grill sausages on a sunny day.
Smartphones – Mobile phones that offer advanced capabilities beyond traditional calling and texting – He uses his smartphone to check his emails and social media.
Touchscreens – Display screens that respond to the touch of a finger or stylus – The new laptop has a high-resolution touchscreen for easy navigation.
Resistive touchscreens – A type of touchscreen that relies on pressure to register touch input – The resistive touchscreen on the old mobile phone required more pressure to operate.
Capacitive touchscreens – A type of touchscreen that uses the electrical properties of the human body to detect touch input – Most modern smartphones and tablets use capacitive touchscreens.
Conductive substance – A material that allows the flow of electric current – Copper is a highly conductive substance commonly used in electrical wiring.
Electric circuit – A path along which electric current flows – The lightbulb wouldn’t turn on because there was a break in the electric circuit.
Nodes – Points or junctions in a circuit where two or more components are connected – The technician identified a faulty node in the network that was causing the connection issues.
Human body – The physical structure of a human being – Regular exercise is important for maintaining a healthy human body.
Wet hands – Hands that are moist or damp with water or another liquid – She dried her wet hands with a towel after washing them.
