Today I completed the basic touch screen driver. The task included
- Learning the "Theory of Operation" of 4 wire resistive touch screens.
- Learning the about the working of AD7843 touch screen controller IC.
- Learning about the SPI peripheral of STM32
- Writing basic SPI drivers (to init, read and write to SPI1)
- Writing basic drivers to command and read AD7843 touch screen controller.
- Filtering the touchscreen data using Median Filter to remove noise.
- Learning about the three point touch screen calibration method.
- Writing a routine to convert touch screen co-ordinate (ranges from 0-4095 in X and Y direction) to LCD co-ordinates.
- Finally ploting a cross-hair at the touched point.
The final result is shown below.
Then I moved on to implement a GUI 3D Button.
After that I went to try a “Free Hand Drawing” application. And what I made is shown in the video below.
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