AM335x Touchscreen Controller - DAC instead of touchpanel

Felix Reinold

My config looks like this: Instead of a 4-wire touchpanel i use a dac to feed the controller with different voltages for simulating the touches.
The first dac is connected to AN0 (XPUL) the second to AN2(YPLL) and the output voltage range is 0-1,25V with a resolution of 0,05V (touchcontroller with internal voltage reference). For switching the voltage on/off I use simple npn transistors.

1st question: Do i use the right pins of the touchcontroller for the dac output?
2nd question: I already made a few tests. Generally nothing happens but sometimes i get touches in the middle of the screen or in one corner, i can't figure out what's the reason (maybe wrong pinning, could the npn transistor be the reason?).

It would be really great if someone can help me!

Thanks

over 12 years ago

0 Biser Gatchev-XID over 12 years ago

TI__Guru**** 393215 points

Hi Felix,

The following pins are used for 4-wire resistive touchscreen:

AIN0 - X Left

AIN1 - X Right

AIN2 - Y Up

AIN3 - Y Down

0 Toshe Mitev over 12 years ago in reply to Biser Gatchev-XID

Prodigy 20 points

Hello Biser,

I would like to know about pin assignment for 5-wire, 8-wire configuration as well as driver config/modification if necessary.

Thank you

0 Miroslav Kiradzhiyski XID over 12 years ago in reply to Toshe Mitev

TI__Mastermind 25235 points

Hi Toshe,

Signals AIN0 - AIN7 are used for the TSC/ADC. The TSC pins are always mapped first, so for 5-wire mode, the TSC signals will be AIN0 - AIN4, and for 8-wire mode, the TSC signals will be AIN0 - AIN7. For more information please read the AM335x ADC Driver's guide.

Best regards,
Miroslav