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Cacodemon
Posts: 21
Joined: Mon Jul 09, 2018 4:32 pm

RB-TFT3.5 pin usage

Mon Jul 09, 2018 4:51 pm

I bought a touch display for my Raspberry Pi some time ago. It's been pretty cool not having to plug my Pi into my PC screen anymore, but recently I've been thinking if I could also attach another hat to my Pi without having to remove the touch display. This one is using GPIO pins only, but I couldn't find resources on the display's pin usage. This far I've checked my retailer's site, the manufactorer's site (Joy-IT) and pinout.xyz but got nothing. The manufacturer has published only the basic installation guide of this touch screen model apparently.

I'm still quite a beginner regarding to how to figure out which pins are being used by which hat, unless it can be checked on sites such as pinout.xyz. With that in mind, could anyone help me out figuring which pins RB-TFT3.5 touch display is using, so I could then determine if another hat can be used in parallel with it through GPIO expansion board for example? I would appreciate it!

DirkS
Posts: 10516
Joined: Tue Jun 19, 2012 9:46 pm
Location: Essex, UK

Re: RB-TFT3.5 pin usage

Wed Jul 11, 2018 7:05 am

There are probably some driver entries in /boot/config.txt that could tell us more about the GPIO usage.
Can you post those entries (or the complete file, preferably in code tags).

The back of the PCB quite often has a lot of info on it. Can you post a photo of that

At a guess I would say that it probably doesn't use the physical pin 29-40 and the i2c (physical pins 3 and 5) and uart (pins 8 &10)

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Cacodemon
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Re: RB-TFT3.5 pin usage

Sat Aug 04, 2018 7:04 am

Sure. I had to install raspbian using their customized image given here (1.2) since I had trouble getting the touch screen work after trying to set it up manually. So, the boot/config.txt is just as it has been since installing that image.

Code: Select all

# uncomment if you get no picture on HDMI for a default "safe" mode
#hdmi_safe=1

# uncomment this if your display has a black border of unused pixels visible
# and your display can output without overscan
#disable_overscan=1

# uncomment the following to adjust overscan. Use positive numbers if console
# goes off screen, and negative if there is too much border
#overscan_left=16
#overscan_right=16
#overscan_top=16
#overscan_bottom=16

# uncomment to force a console size. By default it will be display's size minus
# overscan.
#framebuffer_width=1280
#framebuffer_height=720

# uncomment if hdmi display is not detected and composite is being output
hdmi_force_hotplug=1

# uncomment to force a specific HDMI mode (this will force VGA)
hdmi_group=2
hdmi_mode=4

# uncomment to force a HDMI mode rather than DVI. This can make audio work in
# DMT (computer monitor) modes
#hdmi_drive=2

# uncomment to increase signal to HDMI, if you have interference, blanking, or
# no display
#config_hdmi_boost=4

# uncomment for composite PAL
#sdtv_mode=2

#uncomment to overclock the arm. 700 MHz is the default.
#arm_freq=800

# Uncomment some or all of these to enable the optional hardware interfaces
dtparam=i2c_arm=on
#dtparam=i2s=on
#dtparam=spi=on

# Uncomment this to enable the lirc-rpi module
#dtoverlay=lirc-rpi

# Additional overlays and parameters are documented /boot/overlays/README

# Enable audio (loads snd_bcm2835)
dtparam=audio=on
dtparam=spi=on
dtoverlay=joy-IT-Display_Driver-35a-overlay:rotate=270,swapxy=1
start_x=1
gpu_mem=128
enable_uart=0
Back of the screen

Obviously physical pins 20-40 would be free in any case but I doubt all of those 1-20 are in use either.

DirkS
Posts: 10516
Joined: Tue Jun 19, 2012 9:46 pm
Location: Essex, UK

Re: RB-TFT3.5 pin usage

Sat Aug 04, 2018 7:40 am

Seems to be a waveshare 3.5 (clone?).
That uses SPI0.0 and 0.1 (see https://pinout.xyz/pinout/spi) plus GPIOs 17, 24 and 25 (physical pins 11, 18 and 22)

See https://www.waveshare.com/product/3.5inch-RPi-LCD-A.htm for the pin usage.

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Cacodemon
Posts: 21
Joined: Mon Jul 09, 2018 4:32 pm

Re: RB-TFT3.5 pin usage

Sat Aug 04, 2018 10:16 am

The screen being a clone would explain the lack of resources on Joy-IT's site! Might require some additional testing for my part, but hopefully toying with additional hats will become simpler as there's more info on the Waveshare product. Thanks for the help, I appreciate it!

DirkS
Posts: 10516
Joined: Tue Jun 19, 2012 9:46 pm
Location: Essex, UK

Re: RB-TFT3.5 pin usage

Sat Aug 04, 2018 12:35 pm

Cacodemon wrote:
Sat Aug 04, 2018 10:16 am
The screen being a clone would explain the lack of resources on Joy-IT's site! Might require some additional testing for my part, but hopefully toying with additional hats will become simpler as there's more info on the Waveshare product. Thanks for the help, I appreciate it!
Well I decompiled the dtb file and apart from the 'waveshare35a' text in it, all the GPIO were the same...

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