Using and Understanding Touchscreens

Programmable devices often require both inputs ( keyboards, tempature sensors, mice ) and outputs ( screens, sound amplifiers, motors ).  The development of a touchscreen allowed both inputs and outputs to be combined into a single module.  A touchscreen uses a mathematical coordinate system and an electronic input device built into the screen.The adjective "Cartesian", used to describe this system, honours the name of the mathematician Renee Descartes.

  • In this phone , shown here, the finger touching the screen creates a small voltage drop at that point on the screen.
  •   Most modern touchscreens use a capacitor sensor to detect a finger.  The finger provides a negative earth point on the screen.
  • The finger acts like an input sensor which the Arduino uses to react with the graphic objects at that screen coordinate.
  • Sample code might look like this setCursor(130,142)
  • In the touchscreen shown here a very small screen is worn on the wrist.  It uses a coordinate system to detect the position of the finger.
  • When drawing a graph in a mathematics class, the coordinates may have negative coordinates.
  • When drawing a pixel on the TTGO watch the coordinates are positive.  They are never negative.  The negative number creates a coding translation problem.
  • An example of a coordinate change from a graph to a screen is the point (100,-100) would become (100,100)

Tasks and Activities

  1. What is a "touchscreen" ( please do not copy or paste an Internet definition )
  2. How do most touchscreens work?
  3. How does the touchscreen coordinate system differ from a cartesian coordinate in a mathematics class  (Hint! Read the dot points above)
  4. On a typical touch screen watch what is the probable coordinate of the top left hand corner?

 

  
  1. Descartes ( the mathematician ) developed the coordinate system to link ge......... and al............ branches of mathematics.   ( Hint! Look at this web page )

Don't forget to email your choices/answers to Mr. Widmer by the end of this week.  Keep a copy of that email in your Google Docs folder.