Linux/AM3352: ADC voltage in 5-wire resistive touchscreen

Jian Zhou

Intellectual 1930 points

Part Number: AM3352

Tool/software: Linux

Hi expert,

My customer now bring up the 5-wire resistance touch screen based on AM3352, and they find that voltage of VIN and VDD_ADC is about:

1.785

1.807

It has about 0.022V difference value between VIN and VDD_ADC and the resistance touch screen can not work normally, is it normal?

over 6 years ago

0 Biser Gatchev-XID over 6 years ago

TI__Guru**** 393215 points

Voltage on AIN inputs in TS mode is not necessarily a criteria. In this mode voltage can be sourced from the AIN pins. How is the TS connected? What is the Linux version used?

0 Jian Zhou over 6 years ago in reply to Biser Gatchev-XID

TI__Intellectual 1930 points

Biser,
Customer use the latest SDK, and do we have the HW reference design for the 5-wire resistance touch screen?
In customer's case, AM3352 receive many pen down event after a finger press, and they also want to know the logic of pen up event.
Thanks!

0 aojiang xie over 6 years ago in reply to Jian Zhou

Prodigy 50 points

Hi expert
In my case, AM3352 receive many pen down events rather than 1 pen down event after a finger press up, which element should cause this issue? and we also want to know the detailed logic of pen up event for the future debugging .

0 Biser Gatchev-XID over 6 years ago in reply to aojiang xie

TI__Guru**** 393215 points

Refer to this post by Tyler for the correct wiring: e2e.ti.com/.../931189

I have asked the Linux team to address the SW issues. They will respond here.

0 aojiang xie over 6 years ago in reply to Biser Gatchev-XID

Prodigy 50 points

Can you give me the reference the circuit principle diagram about 5-wires resistive touchscreen in HW way?

0 Biser Gatchev-XID over 6 years ago in reply to aojiang xie

TI__Guru**** 393215 points

This is the HW connection diagram:

I don't understand what else you mean.

0 Nick Saulnier over 6 years ago in reply to aojiang xie

TI__Guru 71925 points

Hello Aojiang & Jian,

Are you both working on the same project? if so, great. If you are not on the same project, Aojiang may need to start a new thread so we do not get your projects mixed up.

As far as I understand it, we would expect pen down events to continue occurring for as long as the finger was touching the screen (to allow us to detect motions like swiping a finger along the screen), and then there would be a single pen up event when the finger is lifted. I am checking with our touchscreen experts to verify how the ti_am335x_tsc.c driver works.

Regards,
Nick

0 Jian Zhou over 6 years ago in reply to Nick Saulnier

TI__Intellectual 1930 points

Nick,

Thanks for your support, it is the same project, Aojiang is our customer.

0 aojiang xie over 6 years ago in reply to Biser Gatchev-XID

Prodigy 50 points

Can you give me the demo design?

0 aojiang xie over 6 years ago in reply to Nick Saulnier

Prodigy 50 points

The problem is that when the finger is lifted the driver cannot detect a pen up event interrupt.

0 Nick Saulnier over 6 years ago in reply to aojiang xie

TI__Guru 71925 points

Hello Aojiang,

Could you share your device tree settings for tsadc? Could you also share the event output you see when a touch occurs?

I misspoke earlier: it looks like an "pen down" IRQ / TRN_TOUCH = 1 event should only be generated once when the touch starts, and then we should get a "pen up" IRQ / BTN_TOUCH = 0 event when the user lifts their finger. I've been told that you should not have to do extra steps for the driver to generate a "pen up" interrupt.

Regards,
Nick

0 aojiang xie over 6 years ago in reply to Nick Saulnier

Prodigy 50 points

My Software SDK Verison is 6.0.

The relate code is that:

static struct tsc_data am335x_touchscreen_data = {

.wires = 5,

.x_plate_resistance = 200,

.steps_to_configure = 5,

}

0 Nick Saulnier over 6 years ago in reply to aojiang xie

TI__Guru 71925 points

Hello Aojiang,

I made an assumption earlier - When Jian said you had the most recent SDK, I thought he was referring to Processor Linux SDK 4.02 or 4.03. The touchscreen driver has changed a lot between AM335x Linux SDK 6.0 from 2013 and the current SDKs from 2017/2018.

1) Could you verify your SDK?
2) Could you post the serial output you see when a touch occurs?

Regards,
Nick

0 aojiang xie over 6 years ago in reply to Nick Saulnier

Prodigy 50 points

Hello Nick,

I used the latest version, the problem still exists.

Do you have 5-wire resistive touchscreen demo design?

aojing

0 Nick Saulnier over 6 years ago in reply to aojiang xie

TI__Guru 71925 points

Hello Aojing,

I am not aware of any demo designs. While I check to see if we have any designs, please

1) verify your SDK
2) post the serial output you see when a touch occurs

Regards,
Nick

0 Nick Saulnier over 5 years ago in reply to aojiang xie

TI__Guru 71925 points

Hello Aojing,

TI has not made any reference designs that use 5-wire resistive touch.

Regards,
Nick

0 Nick Saulnier over 5 years ago in reply to aojiang xie

TI__Guru 71925 points

Hello Aojing and Jian,

I'm going to mark this thread resolved. If we can offer any more help, please post a reply.

Regards,
Nick

0 aojiang xie over 5 years ago in reply to Nick Saulnier

Prodigy 50 points

I don't think there is proof that Am335x can support 5-wire resistive touchscreen.

0 Nick Saulnier over 5 years ago in reply to aojiang xie

TI__Guru 71925 points

Hello Aojiang,

Whether AM335x can support 5-wire resistive touchscreen:

TI does not have any 5-wire resistive touchscreen EVM designs, so 5-wire functionality is not validated on each release of Processor Linux SDK. HOWEVER - the drivers have been tested on non-TI 5-wire resistive touch boards in the past (see this post).

Reference 5-wire design:

Please look up the 4DCAPE-70T Datasheet - the 5-wire schematics are in the second half of the datasheet. This is NOT a TI design and NOT supported by TI, but it shows 5-wire resistive touchscreen designed for use with a beaglebone black.

What TI can do for you:

TI cannot test the driver for you because we do not have the 5-wire hardware. However, if you are using a recent release of Linux Processor SDK we can help you debug and help provide a software patch if needed like we did in this post.

I need these things from you if you want help:

1) what version of Linux Processor SDK you are using, and the version of the Linux kernel being loaded onto the board

2) debug output from the command line

3) all your device tree settings for touchscreen/ADC

Regards,

Nick

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Linux/AM3352: ADC voltage in 5-wire resistive touchscreen