27-12-2012, 04:25 PM
Interfacing Touch screen via lpc21xx
[attachment=45452]
INTRODUCTION
Resistive touch screens can be a great way to enable complex user input in your projects inexpensively and with a minimum number of pins.
With just four wires you can capture gestures, buttons clicks, constantly track the position of a finger or stylus, and other interesting things. Best of all ... thanks to the success of current touch-enabled devices like the Nintendo DS, there is also a steady supply of inexpensive touch screens available (which is precisely why we've chosen to use the Nintendo DS touch screen as an example).
Operation of touch screen
Resistive touch screens operate on the same principle as a simple potentiometer ... you apply 3.3v and GND on opposite ends, and measure the resulting current in between the two on a third pin (using an analog to digital converter).
The only diturning a dial, you adjust it by touching a certain part of the screen. Like a potentiometerfference is that rather than adjusting the resistance by, the resistance varies depending on the position you touch, allowing you to accurately determine exactly where you are touching
Reading method
To read the current position on one axis, you simply need to apply 3.3V on one side, GND on the other, and measure the current on the bus running 'across' the axis you wish to check (see the diagrams and table below for an example of how to read both the X and the Y axis):
PCONP register in lpc2148
Power control for peripherals (PCONP) allows you to turn the internal peripherals of the microcontroller (for example USB, analog to digital converters, etc.) on or off.
The advantage of doing this is that you can save power by turning off any peripherals that you aren't using, which can make a big difference if your device is running off batteries or a similarly 'limited' power source.
[attachment=45452]
INTRODUCTION
Resistive touch screens can be a great way to enable complex user input in your projects inexpensively and with a minimum number of pins.
With just four wires you can capture gestures, buttons clicks, constantly track the position of a finger or stylus, and other interesting things. Best of all ... thanks to the success of current touch-enabled devices like the Nintendo DS, there is also a steady supply of inexpensive touch screens available (which is precisely why we've chosen to use the Nintendo DS touch screen as an example).
Operation of touch screen
Resistive touch screens operate on the same principle as a simple potentiometer ... you apply 3.3v and GND on opposite ends, and measure the resulting current in between the two on a third pin (using an analog to digital converter).
The only diturning a dial, you adjust it by touching a certain part of the screen. Like a potentiometerfference is that rather than adjusting the resistance by, the resistance varies depending on the position you touch, allowing you to accurately determine exactly where you are touching
Reading method
To read the current position on one axis, you simply need to apply 3.3V on one side, GND on the other, and measure the current on the bus running 'across' the axis you wish to check (see the diagrams and table below for an example of how to read both the X and the Y axis):
PCONP register in lpc2148
Power control for peripherals (PCONP) allows you to turn the internal peripherals of the microcontroller (for example USB, analog to digital converters, etc.) on or off.
The advantage of doing this is that you can save power by turning off any peripherals that you aren't using, which can make a big difference if your device is running off batteries or a similarly 'limited' power source.