Seeking Help: Mounting Pi Display 3.5 Inch in Front of Printer with Raspberry Pi 4 on back

I’m looking for assistance with mounting my Pi Display 3.5 Inch in front of my printer. Despite having a Raspberry Pi 4 mounted on the back side, I couldn’t get it to work by simply extending the cable. Does anyone have advice on how to achieve this setup effectively? Thank you!

Maybe your cable was badly/or wrong assembled.
Maybe the cable disturbs the SPI bus.
Did you check the display is still working mounted on its supposed place?

when i plug the display directly on Pi it works fine
when I use the extension cable it does not work.
i used a 1meter length FRC cable(photo is just for reference I used 1 meter long cable)

AFAIK these displays are connected via SPI and as such I’m not surprised that it fails when you put a 1m unshielded cable in between.
Likely it is just not intended for this use-case.

  • Maybe with a high quality shielded cable
  • Maybe the driver offers to reduce the SPI speed and you might get some success

I can reduce the cable length to 0.7 meters if I rearrange the mounting place.
which types of shielded cable can you suggest?

There is none, the SPI driver strength is not high enough.

get a DSI display.
I am running a Pi 3B with a Waveshare 4.3" DSI touchscreen using a 1m flexcable without problems.

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I would not make this broad statement. I have seen SPI buses of 1.5m length.
Generally, you are correct. SPI is not meant for this type of application.

Well, DSI is a completely different bus and cannot be compared to SPI driven ones.

I’d recommend not to use this setup, as it probably will be causing more issues than do any good.
You need around 16 wires (some can be saved due to multiple GND, VCC) but getting and setting up a cable is likely more effort / cost compared to getting a display that is meant to be used in this way.

As recommended by @Igl, either get a DSI display or a HDMI one.

I do! I use such a display, so far from broad.

Could you share your wiring information (wire gauge(s) selected along with images)?

If you use the rule of thumb that transmission line effects are negligible for anything less than 1/10th of the signal wavelength, you will find that 1.5m should be good for 20MHz. Doubling that reduces the bandwidth to 10MHz, still plenty fast for what is being discussed here.

1.5m is not a significant length to expect signal degradation for SPI, especially for the data rates used in 3D printers.

Sorry, chances are there’s an issue with your wiring/connectors/board impedance/pull ups-pull downs (that are acting as terminating resistors) that is limiting the length your SPI signals will work with.

I guess @Arshil uses a standard ribbon cable 1,27mm pitch. Ribbon cable - Wikipedia