# Working on Pi3, gibberish on Pi4

**URL:** <https://rpi-rgb-led-matrix.discourse.group/t/working-on-pi3-gibberish-on-pi4/759>\
**Category:** Uncategorized\
**Created:** [December 2, 2023, 10:49am UTC](https://rpi-rgb-led-matrix.discourse.group/t/working-on-pi3-gibberish-on-pi4/759 "2023-12-02T10:49:42Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![Kudzju](https://avatars.discourse-cdn.com/v4/letter/k/59ef9b/32.png) [@Kudzju](https://rpi-rgb-led-matrix.discourse.group/u/Kudzju)\
**Post date:** [December 2, 2023, 10:49am UTC](https://rpi-rgb-led-matrix.discourse.group/t/working-on-pi3-gibberish-on-pi4/759/1 "2023-12-02T10:49:42Z")

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Hello,

I have a chain of 4x 128x64 1/32S panels connected to a Pi3 (Model A+ with 512 Mb) via an Electrodragon Hat.  
When I run the -D0 demo everything works fine (altough there is a little flicker)

This is the command I’m using:  
`sudo ./examples-api-use/demo -D0 --led-cols=128 --led-rows=64 --led-slowdown-gpio=5 --led-chain=4 --led-parallel=1 --led-row-addr-type=3 --led-multiplexing=0 `

![picture 1](https://global.discourse-cdn.com/free1/uploads/rpi_rgb_led_matrix/original/1X/81bae6b3f2b416b3d5205b200367c30c45bfd031.jpeg)

When I take out the SD card and put it into a Pi4 (tried 2 Model B’s, one with 2Gb and one with 4Gb, with the same Electrodragon hat) and run the exact same command, the display is unrecognizable: dots and horizontal stripes are shown where the rotating square is supposed to be. (See picture 2).

Picture 2 command: same as picture 1 command  
 ![Picture2](https://global.discourse-cdn.com/free1/uploads/rpi_rgb_led_matrix/original/1X/4d548b5ef147f7423b06c3d9a66d58f71b7ec621.jpeg)

Changing `slowdown-gpio` slightly improves the displaying. With a value of 2 I can - sort of- distinguish the rotating square, however the image is still very very malformed with a lot of horizontal stripes in the neigboorhoud (see picture 3).

Picture 3 command (best result on Pi4):  
`sudo ./examples-api-use/demo -D0 --led-cols=128 --led-rows=64 --led-slowdown-gpio=5 --led-chain=4 --led-parallel=1 --led-row-addr-type=3 --led-multiplexing=0 --led-slowdown-gpio=2 `

![Picture3](https://global.discourse-cdn.com/free1/uploads/rpi_rgb_led_matrix/original/1X/56635bca4a3cd03fb5a4968f0b81c48e40f3f462.jpeg)

I experimented with the various swithes like `--led-pwm-lsb-nanoseconds`, `--led-no-hardware-pulse` and `--led-slowdown-gpio` (tested from 1 up to 5) but I could not get the image as it is supposed to be.

Any suggestions on this would be greatly appreciated!

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**Author:** ![megashub](https://yyz2.discourse-cdn.com/free1/user_avatar/rpi-rgb-led-matrix.discourse.group/megashub/32/321_2.png) [@megashub](https://rpi-rgb-led-matrix.discourse.group/u/megashub)\
**Post date:** [December 6, 2023, 8:01pm UTC](https://rpi-rgb-led-matrix.discourse.group/t/working-on-pi3-gibberish-on-pi4/759/2 "2023-12-06T20:01:42Z")

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Caveat: I’m using an older version of this library via a forked project: [GitHub - jenissimo/pico8-led: Run pico-8 and display it on the LED matrix](https://github.com/jenissimo/pico8-led)

With that version of the library, for what it’s worth, my Pi 4B 4GB works fine using the following arguments: `--led-rows=64 --led-cols=128 --led-chain=2 --led-slowdown-gpio=4 --led-brightness=80`

I resolved any remaining minor flicker via tuning my PSU’s voltage dial.

One thought: What happens if you temporarily reduce the number of panels in your chain to 2? Does the behavior change at all?

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**Author:** ![jackjacquejack](https://avatars.discourse-cdn.com/v4/letter/j/34f0e0/32.png) [@jackjacquejack](https://rpi-rgb-led-matrix.discourse.group/u/jackjacquejack)\
**Post date:** [December 19, 2023, 6:36pm UTC](https://rpi-rgb-led-matrix.discourse.group/t/working-on-pi3-gibberish-on-pi4/759/3 "2023-12-19T18:36:08Z")

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see if the --led-slowdown-gpio=4 sorts it. =)