Intro

I found on the internet (www.ledsee.com) a very cheap, only € 17,95 128*64 graphic display with touchscreen. It was sold with a controller for the touchscreen, but it would be nicer to read the touchscreen with the ad-converter that's build in much of the avr processors.

The big advance of a touchscreen is that all is in the software. If you make the traditional keypad and you need an extra key, or maybe change the key layout. It's not possible, or I will cost you money. For the touchscreen just write some code and finished.

The display has a Ks-108 controller, so controlling the display is easy, Mark has done all the work for this.

For this display a different datasheets on the net all with other connections. After some research the correct connections are;

1	Cs1	11	Db2
2	Cs2	12	Db3
3	Gnd	13	Db4
4	+5V	14	Db5
5	Contrast	15	Db6
6	Cd	16	Db7
7	Read	17	Reset
8	Enable	18	Negative pwr
9	Db0	19	Backlight A
10	Db1	20	Backlight K

Pin 18 generates a negative voltage to drive the contrast for the display, this is not really necessary the circuit below works just fine for me.

Circuit diagram

I didn't connect pin 19 & 20 for the backlight. If you close the jumper (figure 1) on the back of the display the backlight it's connected with the display's powersupply. Also here you can see how to connect the touch screen with the Avr. In the circuit diagram there are some resistors in series with the touchscreen. This is not really necessary, but only for protecting the avr if you make a program mistake and shorting the io pins.

Figure 1

The basics of a touch screen

The touchscreen that's used here is a 4 wire resistive touchscreen. It's not more then 2 big resistors, one with the connection leads to the top and the other with the leads to the side. By pressing on the screen your making contact between the top and bottom layer. To determine the cordinates you read first the x value and then the y value. To say it simple;

Touchscreen x read, Set PF0 high and PF2 low and read PF1 or PF3.

Touchscreen y read, Set PF1 high and PF3 low and read PF0 or PF2.

Figure 5

The application note

First of all i created a virtual keypad on the touchscreen.

Figure 4

I have chosen for a 3x4 matrix where the upper row is smaller.

To determine the values as shown in figure 4, unremark the “Print Value” lines in the subroutine “Readtouch”, we need those values in the “Whichkey” subroutine to determine the begin and end of each key.

The buttons that i have used are 32x24 pixels. This is a nice size that you can operate with your finger.

The build in font's of the display or bascom are too large for my application so i draw my own buttons with build in fonts, see the bmp's in the download file.

The result

The BIG guys are using a calibration function, temperature compensation, but i don't think this is necessary for such small screen.

And here is the result created with the source code below:

Figure 2 Mainmenu

Figure 3 LichtEetafelmenu (menu 13)

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