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Using the touch screen of the CFAF320240F 035TTSCB

mpholmes

New member
I'm trying to get the touch screen to work. I have xLow and xHigh become inputs, and yLow and yHigh become outputs, set yLow to 0, yHigh to 1, and then do an AD sample on xHigh. Then I swap things so the x's become the outputs, and the y's become the inputs. It's not working. Has anyone gotten it to work doing this route, rather than a special dedicated chip for dealing with the touchscreen?
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mpholmes

New member
OK, it works, but when you aren't touching the screen, the x and ys fall SLOW toward 0. Is it standard to put a pull down resistor on the A/D inputs to help it along? I don't want to wait 30 seconds before I know someone isn't touching the screen. haha.
 

mpholmes

New member
It does work much better with pull down resistors (1k I'm using) from each AD input to ground. Now it takes about less than 1/10 second for the A/D input to read ZERO when you transition from touching the screen to removing your finger. Similarly, it takes about 1/10 of a second, or slightly more for the A/D result to settle on the point that your finger is touching.
 

mpholmes

New member
It does work much better with pull down resistors (1k I'm using) from each AD input to ground. Now it takes about less than 1/10 second for the A/D input to read ZERO when you transition from touching the screen to removing your finger. Similarly, it takes about 1/10 of a second, or slightly more for the A/D result to settle on the point that your finger is touching.
better make that a 20kOhm. haha. Does anyone know the impedance of the resistive network on the touchscreen?
 
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