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I now have a Raspberry Pi 3B, and a 3.5inch touch screen. The screen connects to the Pi by connecting to GPIO pin 1 to 26, so it holds up all the UART and I2C pins. However I would want to connect another device to the Pi by serial. Is there any possible way to achieve this with the remaining pins, like by emulation or something?

I have looked at many screens but they all seem to hold up GPIO 1 to 26, even for some ones that has HDMI connection, I suspect they use the GPIO to pull power. Does there exist any screen that does not hold up all the GPIOs?

Is it possible to initiate a parallel connection from I2C 3 and 5 while the screen is connected?

Or should I simply use the usb ports and connect to a USB-to-serial device?

I simply want to build a Raspbian with display and barcode scanning ability, perhaps there are better ways to go?

UPDATE:

Just a bit of update, I think I should be using USB instead so the question asked was no longer an issue, and did found a monitor that does not hold up the unused slotsKeDei Screen.

But I think pico hat hacker is the correct answer for this question, in fact I have just ordered one. so I am going to credit Mat for the answer, and thankyou Steve for your insight.

Jimmy Chi Kin Chau
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  • You don't mention what pins your screen uses if it uses the tx/rx pins you may need to use the USB ports, but if there are no pin conflicts you could use something like this https://shop.pimoroni.com/products/pico-hat-hacker. These come in two or three variations (based on size) I only linked to the most recent/smallest. – Steve Robillard Aug 02 '17 at 10:56
  • this has some additional ideas https://raspberrypi.stackexchange.com/questions/3475/how-to-get-more-than-one-uart-interface – Steve Robillard Aug 02 '17 at 11:05
  • Do you have any specifications or (unlikely) schematics for the screen? Without knowing why the screen needs all of the GPIO pins, we can't say whether the RX/TX pins are usable when the screen is connected – DividedByZero Aug 02 '17 at 12:22
  • Try connecting the screen and running a program that uses the serial pins (a simple loopback should suffice). If the screen and program both behave as expected, you then just need to branch the pin. If either of the two start doing weird things (which they probably will), you can't use both together. USB to serial would be fine, however. – DividedByZero Aug 02 '17 at 12:35
  • Yes, thankyou for all your comments, the screen came with a 2x13 inlet so I just assumed it uses up all the pins. Pico hat hacker seems the way to go. I just got it off taobao in China so there is not much documentation coming with it. The extra dimension seems a bit of concern but I think thats the price to pay. – Jimmy Chi Kin Chau Aug 02 '17 at 13:33
  • @SteveRobillard Just out of question, will soldering to the bottom of the Pi board also work? – Jimmy Chi Kin Chau Aug 02 '17 at 14:58
  • If you are good with an iron you could solder a wire to the underside of the board; just be careful to remember that the pins are reversed left to right. – Steve Robillard Aug 02 '17 at 17:59
  • @SteveRobillard, yes I mean the underside, sorry for the sloppy English. – Jimmy Chi Kin Chau Aug 03 '17 at 00:45

2 Answers2

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If its Adafruits 3,5 "

https://learn.adafruit.com/adafruit-pitft-3-dot-5-touch-screen-for-raspberry-pi/overview

Uses the hardware SPI pins (SCK, MOSI, MISO, CE0, CE1) as well as GPIO #25 and #24. GPIO #18 can be used to PWM dim the backlight if you like. All other GPIO are unused.

And YES you have to get a breakout as the Pico HAT Hacker from Pimoroni or eq to access the unused GPIOs.

MatsK
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  • What does the link have to do with the OP's question? The first line of his question says he has a 3.5 inch screen. – Steve Robillard Aug 02 '17 at 12:03
  • The screen connects to the Pi by connecting to GPIO pin 1 to 26. Without knowing the brand I gave a example from the screen I have... – MatsK Aug 02 '17 at 12:08
  • In general, it is better not to guess or assume, that is what comments are for. – Steve Robillard Aug 02 '17 at 13:03
  • Agree, but if you have surveyed the market, you will notice that there are a few variants of these kind of products and they interface quite the same, so it is a assumption that is well founded. – MatsK Aug 02 '17 at 13:21
  • Thanks Mat and Steve for your information, yes as Mat mentioned pretty much every screen I have came across seemed to have that configured outlook, in fact mine was visibly identical to what is in the link. – Jimmy Chi Kin Chau Aug 02 '17 at 13:34
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GPIO "functions" such as SCK, MOSI, MISO, CE0, CE1 etc. are programmable at register level.

Jan Hus
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