leomeyer
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Gertboard and touchscreen display?

Tue Aug 19, 2014 11:55 am

Hi, another question from a noob here.

Is there a way to combine a touchscreen display, for example the Adafruit PiTFT, with a Gertboard?

Thanks for suggestions,
Leo

leomeyer
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Joined: Tue Aug 19, 2014 7:00 am

Re: Gertboard and touchscreen display?

Tue Aug 19, 2014 3:42 pm

OK, just in case this question seems too nooby, I'd like to hook a Gertboard and a touch display to an RPi at the same time; has anybody done this before and could give me some info on what works and what not?

Thanks, Leo

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Gert van Loo
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Re: Gertboard and touchscreen display?

Tue Aug 19, 2014 3:53 pm

Most touch screens use an I2C interface which is the one interface the Gertboard does not use.
So yes, I think it is possible.

PiGraham
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Re: Gertboard and touchscreen display?

Tue Aug 19, 2014 4:02 pm

Gert van Loo wrote:Most touch screens use an I2C interface which is the one interface the Gertboard does not use.
So yes, I think it is possible.
I think most small (2 - 4 inch) touchscreens (e.g. Texy's and AdaFruit PiTFT) use SPI. One channel is display and the other is touchscreen.

Adafruit wrote:Uses the hardware SPI pins (SCK, MOSI, MISO, CE0, CE1) as well as GPIO #25 and #24. All other GPIO are unused.

leomeyer
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Re: Gertboard and touchscreen display?

Wed Aug 20, 2014 6:36 am

PiGraham wrote: I think most small (2 - 4 inch) touchscreens (e.g. Texy's and AdaFruit PiTFT) use SPI. One channel is display and the other is touchscreen.

Adafruit wrote:Uses the hardware SPI pins (SCK, MOSI, MISO, CE0, CE1) as well as GPIO #25 and #24. All other GPIO are unused.
Thanks a lot. I have now read a bit more; what I found is that as long as I don't use SPI and GPIO #25 and #24 I should be fine with running Gertboard and PiTFT in parallel. Probably this means I can't use D/A and A/D but I'm fine with that. The ATmega communication should work too.

Please let me know if I misunderstood something.

PiGraham
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Re: Gertboard and touchscreen display?

Wed Aug 20, 2014 7:10 am

leomeyer wrote:
PiGraham wrote: I think most small (2 - 4 inch) touchscreens (e.g. Texy's and AdaFruit PiTFT) use SPI. One channel is display and the other is touchscreen.

Adafruit wrote:Uses the hardware SPI pins (SCK, MOSI, MISO, CE0, CE1) as well as GPIO #25 and #24. All other GPIO are unused.
Thanks a lot. I have now read a bit more; what I found is that as long as I don't use SPI and GPIO #25 and #24 I should be fine with running Gertboard and PiTFT in parallel. Probably this means I can't use D/A and A/D but I'm fine with that. The ATmega communication should work too.

Please let me know if I misunderstood something.
It won't enough to not use a device, if it's connected it will conflict. You may be able to disconnecte SPI signals on the Gertboard, but that's not ideal.

What features of Gertboard do you need? You can get i2c port expanders and lots of other devices.

PiGraham
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Re: Gertboard and touchscreen display?

Wed Aug 20, 2014 7:41 am

I found a 7 inch TFT touchscreen that has I2C interface for display and touchscreen, but that isn't it's default configuration. Most screens will use SPI for display because it's a faster interface.

Perhaps you could use a USB connected screen, or display on HDMI and touch on I2C.

leomeyer
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Re: Gertboard and touchscreen display?

Wed Aug 20, 2014 8:13 am

Are the SPI pins hardwired somewhere? I was under the impression that they go to the connectors only, so if I don't connect them using jumper cables I should be fine; they should be routed in theory to the display stacked on top of the Gertboard.

Perhaps I should really use a different IO board. I require at least five open collector outputs (for driving two 24V/2A motors using a half-bridge driver L298), at least seven buffered outputs and two or more inputs. I also want to control four 230V phase cutting channels on a separate board, that's why I liked the Atmega328 for interfacing purposes. So I reckoned the Gertboard would be fitting nicely, but I may be mistaken.

I'll try to evaluate other displays as you hinted, thanks.

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Gert van Loo
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Re: Gertboard and touchscreen display?

Wed Aug 20, 2014 8:35 am

Are the SPI pins hardwired somewhere?
No, all GPIO I/O pins are freely available and you can mix-and-match as much as you like.

PiGraham
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Re: Gertboard and touchscreen display?

Wed Aug 20, 2014 9:33 am

leomeyer wrote:Are the SPI pins hardwired somewhere? I was under the impression that they go to the connectors only, so if I don't connect them using jumper cables I should be fine; they should be routed in theory to the display stacked on top of the Gertboard.
Ah, apologies to Gert, I'm not familiar with the Gertboard. If you chose what IO to patch to what devices then you can leave the SPI unconnected on the Gertboard and use it for the TFT/Touch. If Gertboard runs OK without SPI (just losing the SPI-specific functions) then Problem solved.

leomeyer
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Re: Gertboard and touchscreen display?

Wed Aug 20, 2014 1:45 pm

OK, that sounds great. Gonna get me the hardware then ;-)

Thanks a lot!

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