horatio
Posts: 4
Joined: Mon Apr 23, 2018 5:25 am

Capacitive touchscreen + controller board for Raspverry Pi

Mon Apr 23, 2018 6:09 am

Hi, I've just bought my first Raspberry Pi (3 B+), and now I'm trying to build a Raspberry Pi smartphone with it.

Now I'm looking for a 5-inch capacitive touchscreen. I found the following touchscreen that seemed perfect, but for the physical flexibility I wanted the display and the board separately.

5-Inch-800x480-Capacity-Touch-Screen SKU: EP-0081
https://wiki.52pi.com/index.php/5-Inch- ... U:_EP-0081

There were some touchscreens on Alibaba. The ones with parallel RGB interface were easy to find. There was even a 1080*1920 high-resolution touchscreen with MIPI DSI interface:

https://www.alibaba.com/product-detail/ ... 99749.html

So I'm trying to find a controller board that works with this display and Raspberry Pi.

There were several DSI to HDMI boards, but the problem is that I coundn't find one with a touch controller.

Should I just go with the already assembled touchscreen & board, or is there any way to use the 1080*1920 display?

Thank you in advance!

horatio
Posts: 4
Joined: Mon Apr 23, 2018 5:25 am

Re: Capacitive touchscreen + controller board for Raspverry Pi

Tue Apr 24, 2018 3:07 am

I found out that there's a more promising option to have an independent touch controller board separately from the DSI to HDMI controller board, rather than to have one combined board, but I'm yet to find the capacitive touch controller that surely works with RPi.

For those who seek a resistive version, there was a perfect item from adafruit:

TFP401 HDMI/DVI Decoder to 40-Pin TTL Breakout - With Touch
https://www.adafruit.com/product/2219

The chip AR1100 seems to be perfect for RPi, with which the touch screen behaves just like an ordinary mouse, but I'm still trying to find the capacitive alternative. I'd appreciate any information. Thank you.

horatio
Posts: 4
Joined: Mon Apr 23, 2018 5:25 am

Re: Capacitive touchscreen + controller board for Raspverry Pi

Mon May 07, 2018 4:09 am

After research, I found out that capacitive touchscreens are more complicated than resistive touchscreens.

Firstly, there are a number of interfaces of the touchscreens. The interface for input can be one tail:

https://www.alibaba.com/product-detail/ ... 6105R6Theu

or two tails:

https://www.alibaba.com/product-detail/ ... 61f67zDsr5

The second tail is for touch obviously (or it is integrated in one tail). So there should be different controller boards for each type.

The official 7 inch Raspberry Pi touch display comes with a controller board that deals with a LVDS, one-tail touchscreen, but they don't sell the board alone.

https://www.raspberrypi.org/products/ra ... h-display/

For two-tail touchscreens, there are of course HDMI to LVDS converters or HDMI to DSI converters that are video-only and don't deal with touch, but I'm still trying to find out how to deal with the second tail (for touch). I at least found out that the interface of the touch tail seems to be I2C, but I'm not sure whether merely connecting the second tail to the Raspberry Pi via an I2C to USB converter would work or not.

So far, the most promising option would be to buy the official 7 inch touchscreen (just for the board) and also a 5 inch, LVDS touchscreen to combine with the official controller board, but I hope there are some smarter ways. I appreciate any information. Thank you for reading.

mbt28
Posts: 29
Joined: Wed Feb 04, 2015 10:35 am

Re: Capacitive touchscreen + controller board for Raspverry Pi

Mon May 07, 2018 12:24 pm

Hi,

Capacitive touch screens you can use if they have i2c or spi interface. Most of the linux drivers are already available.

Otherwise, for I2c to usb I already wrote an arduino firmware which is a usb hid actually but the code is in big mess and I never had a chance to upload it to github. Since I have no interest at all I dont think I will fix it up.

The best is the to use native driver with I2C interface.

For dsi interface, if you are experienced you may try to use anthols driver with dsi screen or with a dsi to lvds bridge. For this please also note that current pi only have 2 dsi lanes available.

horatio
Posts: 4
Joined: Mon Apr 23, 2018 5:25 am

Re: Capacitive touchscreen + controller board for Raspverry Pi

Tue May 08, 2018 11:06 am

Thank you!

Now I know connecting the I2C (or SPI) tail to RPi should work without specially installing additional drivers, and also (after research) that the I2C interface on FFC (Flexible Flat Cable) can connect to RPi's GPIO pins through jumper wires, if I am correct.

It's also good to know that it could be rather more messy to give a role to USB here.

I'm still wondering between using GPIO with I2C tail or just relying on the official driver board by paying more, but thanks to you, now I have all the necessary information to wonder between them.

> if you are experienced

I'm a hopeless application-side programmer who doesn't know things about hardware but decided to tackle this project. Thank you for your help! I will report here after I try either of the choices, and I hope some people who read this thread in the future will also try to make a RPi smartphone or tablet. Good to have genuine Linux on your phone, at least for me.

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