Case of the Zombie Finger: Why Some Capacitive Screens Don’t Respond to Touch?
You may have noticed that sometimes your smartphone does not respond to your touch. There is actually a reason for this (an embedded developer will be able to tell you why). Basically, a capacitive screen, like the one on your smartphone or laptop touchpad, is covered by an electrical field. This electric field is sensitive to conductors. A resistive screen does not have this field, which is why you have to press such screens harder to register your command.
When you bring your finger close to this electric field, your finger absorbs some of the electricity (the human body is a conductor). It creates a disturbance in the field. The disturbance is detected by electrodes just under the screen, which enables the phone to respond to your command.
You don’t even have to touch the screen to make the sensor detect your finger. But if you have callouses on your finger or if you are wearing gloves or if you have dry hands, the conduction of electricity is disturbed and capacitive screen won’t respond.
Other factors can also disturb the capacitive screen. These include grime or grease on the glass and overlapping electrical fields (from charging stations, fluorescent lights and even components in the phone). A software developer has to take these factors into consideration when designing software algorithms for capacitive screens.