jrseriel
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Joined: Fri Mar 31, 2017 7:45 pm

3 touch screens with Rasberry Pi Zero

Sun Apr 02, 2017 1:30 am

I am designing a project to be used with the raspberry pi zero, possibly. Would the raspberry pi zero be able to drive 3 independent 1.8 inch touch screens?

Any input would be greatly appreciated.

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Gavinmc42
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Re: 3 touch screens with Rasberry Pi Zero

Sun Apr 02, 2017 4:16 am

These would be SPI screens?
There is only two CE pins, but these could be muxed with GPIO help.

Drivers?
Price of a Zero, use three of them :lol:
I'm dancing on Rainbows.
Raspberries are not Apples or Oranges

jrseriel
Posts: 6
Joined: Fri Mar 31, 2017 7:45 pm

Re: 3 touch screens with Rasberry Pi Zero

Sun Apr 02, 2017 4:38 am

Correct. These would be three tft screens. What do you mean by 'muxed GPIO'? Consider me a noob of raspberry pi zero.

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Gavinmc42
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Re: 3 touch screens with Rasberry Pi Zero

Sun Apr 02, 2017 6:52 am

Quick SPI lesson
https://en.wikipedia.org/wiki/Chip_select

SS is the slave selector or chip select input.
The Wiki shows SS1, SS2, SS3 but the Pi only has two called CS0, CS1.

A mux or expander can have 2 CS inputs and 4 CS outputs.
It uses an extra GPIO input to select which 2 of the 4 outputs are connected to CS0, CS1

You cannot write to the LCD via the SPI at the same time, you select which one to talk to.
I'm dancing on Rainbows.
Raspberries are not Apples or Oranges

notro
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Re: 3 touch screens with Rasberry Pi Zero

Sun Apr 02, 2017 11:01 am

I guess you're going to use fbtft.

This post talks about adding more chip selects: viewtopic.php?t=157994&p=1028222
Here's a DT overlay with 2 fbtft devices: https://github.com/notro/fbtft/issues/2 ... -290314992

jrseriel
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Joined: Fri Mar 31, 2017 7:45 pm

Re: 3 touch screens with Rasberry Pi Zero

Mon Apr 03, 2017 7:44 pm

It would have to be able to run three of them at the same time, in an extended desktop fashion. This may not be possible.

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Gavinmc42
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Re: 3 touch screens with Rasberry Pi Zero

Tue Apr 04, 2017 4:04 am

It would have to be able to run three of them at the same time, in an extended desktop fashion. This may not be possible.
You could use a FPGA?
The one SPI in from the Pi, to 3 SPI outputs to the LCDs.

Considering the price of FPGA dev tools you might be better off using Pi Zero's and seeing is this works
http://www.piwall.co.uk/

Probably would need to use USB ethernet gadget mode, but that's a bit over the top for your ap.
Maybe there is a micro that has 4 SPI ports, one slave, 3 masters and enough ram to hold the image data.

For weird stuff like this I also go to the Cypress PSoC family, 32bit ARM core with programmable CPLD type blocks
A 4200L micro can fit 4 SPI's no problem, but only 32K SRAM, if you need more you will need to use another chip.
You can get ARM Cortex M0 micros with 256K SRAM.
I'm dancing on Rainbows.
Raspberries are not Apples or Oranges

jrseriel
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Joined: Fri Mar 31, 2017 7:45 pm

Re: 3 touch screens with Rasberry Pi Zero

Tue Apr 04, 2017 5:26 am

I'll check it out! Thank you for the tips!

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