TSC2007: Touch Screen Drivers Interface Y+/Y- cannot work

Are you writing any data to registers? How do you read the data?

Hi Sanjay,

Before issue has been resolved. as now current issue is about the stability of the touch board. Is there any recommended value for the touch board model?

Can you please explain what you mean by touch panel stability ?

Hi Sanjay,

the issue is, when the touch pen slide on the touch panel, the touch point sometimes will not follow the touch pen's slide path, instead it will jump to to the left bottom 

Customer are now using Linux driver and setting as below, 

tsc2007@48 {

              compatible = "ti,tsc2007";

              reg = <0x48>;

              pinctrl-names = "default";

              pinctrl-0 = <&ts_default>;

              interrupt-parent = <&pio>;

              interrupts = <0 0x8>;

              gpio = <&pio 0 0>;

              ti,x-plate-ohms = <650>;

  };

Can you help review if any suggestion?  thanks!

Please send me your schematic

Hi Sanjay,

customer's schematics attached, pls help check !

trk-06-m_tsc2007.pdf

Sometimes switching noise can disrupt behaviour of the touchscreen. We normally suggest 1n capacitors on X+,X-/Y+,Y- pins.

Is there some switching supply in the vicinity? 

Hi Sanjay,

The X+/X-/Y+/Y- routing short in inner L8 layer and surround by ground plane (adjacent layer are also ground ).

The X+,X-/Y+,Y- pins. layout out should be fine, is it ? 

Also customer had tried add 0.01uF on X+,X-/Y+,Y- pins. but problem the same. Should i ask customer try 1nF ? 

is there any thing else we can check? 

thanks!

Is this an intermittent issue or is it always present

Hi Sanjay

This issue is always present and easy to duplicate.

I shall reply shortly

You can try the below.

Remove the touchscreen connections. Take a DC Power supply and connect its output through a 470 ohm resistor to X+ pin.

Take a second DC Supply and connect it with 470 ohm resistor to y+

Fix the Y+Voltage to 1.65v DC. Then shift X+Voltage from 0v to 3v

Does the touch panel create a stable  x coordinate from left to right of screen? 

Hi Sanjay,

Customer had done the test as you suggest. 

Fix the Y+Voltage to 1.65v DC. Then shift X+Voltage from 0v to 3v. 

For 0.7V < X+ < 3V the the touch panel does create a stable  x coordinate from left to right of screen. 

However when X+ < 0.7V we begin to see the touch point is not stable as below video show  

Below video show X+ = 0V the touch point is not stable 

We also had captured the waveform of X+ pin and see a lot of pulse sending out from X+ pin as below  

Any idea what it is ? and any suggestion for next step ?

Let me try to understand the setup.

The Touch panel is removed but the digital output of the TSC is used to put the blue pointer at x,y coordinate.

Is that correct ? 

Is this waveform when you drive the X+ pin with a 470 ohm resistor?  When you increase the level of the DC Voltage Does the bottom level

of the waveform go up. At the DC supply set at 0v does this level go below 0.5V?

Also at position of X+=0 V connect the input side of 470 ohm to ground and let me know if the situation changes

-----------------------

Also as an additional test make x+=1.65v and move the Y+ with the DC Supply. Does this go all the way from top to bottom?

The Touch panel is removed but the digital output of the TSC is used to put the blue pointer at x,y coordinate.

Is that correct ?

JOE:  The touch panel is removed.

          The blue pointer is TSC x,y coordinates under Android.

Is this waveform when you drive the X+ pin with a 470 ohm resistor? 

JOE: I derived X+ and Y+ with 470ohm resistor individually , and connect to adjustable DC power supply PST-3202.

When you increase the level of the DC Voltage Does the bottom level

of the waveform go up. At the DC supply set at 0v does this level go below 0.5V?

JOE:  The bottom level of the waveform is 0.5V when input from 0V to 0.5V.  It will go up when input is over 0.5V.   The X+/Y+ are same behavior.

Also as an additional test make x+=1.65v and move the Y+ with the DC Supply.

Does this go all the way from top to bottom?

JOE:  Base on our SW setting and the test result is as below,

      Fixed X+=1.65v , increase the Y+ form 0V to 3.3V, the pointer goes from left to right.

      Fixed Y+=1.65V , increase the X+ form 0V to 3.3V, the pointer goes from up do down.

Thanks for the detailed reply. Does the Y also show the same jump as the X ?

Hi Sanjay,

Yes, X+/Y+ are the same.  The bottom level of waveform is 0.5V when its DC input from 0V to 0.5V. 

Can you now connect the touch panel. Take a scope shot of the x+Voltage . Move your finger from left to right and see the bottom of the waveform of the

X+. Can you let me know what you see as you move finger to the left of the screen? 

Hi Joe,

from your video it looks that its stable at for moment at the left of the screen. The voltage seems to go from 0 to about 1.8V

Do you possibly have the movement of the waveform where you see the issue on the left of the screen?

Hi Sanjay,

When my finger pressed on the touch panel, the pointer is stable.  But when finger released from panel, the pointer often moves to left-down side.  Please see below video, the pointer has abnormal movement at third time I tried.    Pressing on other location of touch panel, it also has this issue.

Removing the finger off the screen results in the coordinates no longer being present. The y and X coordinates go to 0 and the pointer goes to the bottom of the screen.

I believe this is the expected behaviour