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I'm building a DIY tablet with Orange Pi & A20 SoC (maybe I will change for LeMaker Bass) & Android 4.2.2 (v.5 with Bass). This is a 17.3' screen tablet. I already have a IPS screen, and all works, 4h30 autonomy

Anyway, now I'm looking for a cheap but quality solution for a touch screen. So, multitouch, and easy interface: USB is the better choice for me.

I have seen the "HP ENVY TouchSmart 17 t" touch screen. The others touch screen are about 180$, because not a serial manufacturing... Here a pic of the PCB:

enter image description here

It seems that the chip is eGalax (so no problem for the driver: /drivers/input/touchscreen/usbtouchscreen.c), and the interface looks USB (CN1 ref VDD, D+, D-, Ground).

But, because of norms of USB which is VDD, D-, D+, Ground:

Here, D+ and D- are inversed... It distrub me a little.

So, my question: Does somebody can confirm this is really an USB device ?

Thanks

Edit: Here a second pic, but the PCB is a little different:

enter image description here

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  • \$\begingroup\$ You should be able to see if it is USB if you look up the datasheet of that eGalax chip. The partnumber is hard to read though from the photo. I would be surprised if it is not USB though. \$\endgroup\$ Jul 9, 2015 at 6:16
  • \$\begingroup\$ I think it's eGalax exc7920 but I'm not sure. Here a second photo of the PCB \$\endgroup\$
    – Guillaume
    Jul 9, 2015 at 6:23
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    \$\begingroup\$ OK, I found some info on the EXC7920-EG32 and that has a USB and a UART (serial) interface. For a UART interface it would be silly to use D+ and D- as signal names so I'm quite sure it must be USB. I would just ignore the order of the D+ and D- (in relation to ground and 5V) and connect them as they should be connected. Good luck ! \$\endgroup\$ Jul 9, 2015 at 6:27
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    \$\begingroup\$ It may not be 5V. Internal usb devices are at times 3.3v or different. \$\endgroup\$
    – Passerby
    Jul 9, 2015 at 7:07
  • \$\begingroup\$ Yeah, you helped me, thx a lot. It's in reality EXC7920-SG11 chip. (I can read it now on the pics). So, according to this document, operating voltage is 2.7 to 3.3V and USB 1.1. But I don't know if this operating voltage correspond to D+ and D-, or VDD and Ground. Do you know this ? \$\endgroup\$
    – Guillaume
    Jul 9, 2015 at 10:08

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Some good news, after receive the touch panel (I had to try!)

The chip is Egalax 7920-SG11: enter image description here

The internal connector is very very small, (4mm x 2mm), so I had to found another solution to plug the device. Hopefully, I have found !

There are some plots on the pcb, they are indicated: (thanks HP !)

enter image description here

So, I have soldered an old laptop screen cable (need small wires, each plot is 1 mm diameter) to each point, after checking each connection with a multimeter.

enter image description here

Then, the following is not hard. Here the result, and the Windows detection :)

enter image description here enter image description here

Now, let's go on Linux and Android, the final destination. But it's another story...

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  • \$\begingroup\$ The best: it works with hid-multitouch.ko in Android \$\endgroup\$
    – Guillaume
    Jul 22, 2015 at 14:34

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