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I wanted to rebuild this RPi Zero Project: https://learn.adafruit.com/pigrrl-zero/overview

But instead of paying 50(!) Dollars for a 2.8 Inch TFT i wanted to get some other lcd... I do still need some spare GPIOS for the custom controls (12 GPIOS to be exact). The LCD Display that i wanted to use plugs in with a 2x 20 pin, but doesnt use all GPIOS:

Interface Define:

24--GPIO7 --------> TP_CS

26--GPIO8 --------> LCD_CS

22--GPIO25 --------> TP_irq

23--GPIO11 --------> SPI_CLK

21--GPIO9 ---------> SPI_MISO

19--GPIO10 ---------> SPI_MOSI

5v ---------> 5v

GND ---------> GND

Does this mean that when i define the GPIO Button controls in the Retrogame config and only use GPIOS that are "green" (3.3v) and not used by the LCD, I can just solder jumpers to all the GPIOs That the LCD would need and plug them into the LCD, while using the rest for the controls?

Pinout of my Zero

The Numbers That are written as "GPIO[x]" are the ones sued by the software and listed for the LCD

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Yes, you can wire the LCD to just the pins that it needs. You will have to be careful about large differences in signal wire length due to propagation delay differences causing unpredictable behavior; but aside from that, you should be fine, as the signal is relatively low speed compared to the modern high-speed buses on-board like the CSI and DSI interfaces.

Another option would be to use a ribbon to connect to the display and solder your wires to the bottom of the pi. Some displays, such as the adafruit piTFT, have a second header that allows you to access the unused GPIOs without much extra work.

  • So if i use jumpers with 5-10 cm length it won't have any impact? can i also put switch across the GND jumper to be able to turn the display off? – Steff Jun 4 '17 at 16:55
  • @Steff, Yes that should be fine. but I would recommend placing the switch across the power rails instead of ground. (use a dual pole switch to kill both 5v and 3.3v in one go) Note that this method of disabling the display may cause either the device or the driver to freak out and either go haywire or crash. the piTFT in particular has a GPIO pin for controlling the backlight, which is probably safer. – BaconWaifu Jun 6 '17 at 5:19

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