rm-hull/luma.led_matrix

Display output issue

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Ombruz commented

Hello, I installed all the required drivers, I'm running a 4in1 max7219 display connected to a Raspberry Pi zero W and raspian os.
The display is connected to a separated external 5V power supply.
Python is the latest version, and I had no errors while installing or building dependancies.
While running example scripts to test the display output or any kind of script (clocks, messages etc) the output from the display results in fast flickering bogus symbols, solids squares and random led turning on and off in fast sequence.
I tried to reinstall several times, as well as changing the display, the result is still the same.
Any idea about a workaround? Thank you vey much.

Linux raspberrypi 4.14.62+ #1134 BST 2018 armv6l GNU/Linux

rm-hull commented

Have you got a common ground between the pi and the external 5v supply?

I would try just using the 3.3v power rail from the raspberry pi to isolate any noise issues as the first step. (I have been able to power 12 led matrices from the Pi successfully)

Ombruz commented

I tried either 5v and 3v (including solely from the PI rail), either from the PI and external power sources, still result even with a common ground.
I made a video to show you the display behaviour:
https://www.youtube.com/watch?v=aGjg98i2fpg&feature=youtu.be

Ombruz commented

Good evening,
As suggested I run the spidev_test, and this is the output:
20180918_014748
20180918_014723
According to the output seems there is no RX altough every new instance of the test shows different random static patterns on the display as you can see on the second pic.
I checked the correct connection between the MOSI/SCLK pins, also tried those on SPI1 (pins 20 and 21).
Apparently nothing has changed.
Any idea?
Thank you in advance!

rm-hull commented

Could you take a picture showing the wires going out of the RPi header onto the LED matrix pins?

Can you supply a URL/link where you bought the LED matrices please? Did you solder them yourself or did they come preassembled?

For the SPI test, please remove all / any external wires from the GPIO headers, and as per https://github.com/rm-hull/spidev-test#testing-the-spi-bus, connect pin 19 (BCM 10 = MOSI) to pin 21 (BCM 9 = MISO) to form a loopback connection. If you aren't seeing the same bytes be transmitted as received, then this would be something that needs addressing before we can investigate the LED matrices.

Ombruz commented

Good evening
These are the connection I made between the two MAX7219 4in1 matrix:
20180919_204821

These are the cables from the display:
20180919_204800

And these from the raspi side:
20180919_204731

The test using the loopback connection in the way you suggested resulted satisfactory, reading the same bytes on TX and RX.

The unit come from an online shop called Taobao (a sort of aliexpress) but I can't recall exactly the vendor. I just soldered the two blocks made of 4 display each.

Gadgetoid commented

It's hard to see- but from tracing your wires it seems that you have the "CS" (SPI Chip-Select) pin on your matrix chain connected up to the "SCLK" (SPI Clock) pin on your Pi Zero via the yellow wire, and the "CLK" pin on your matrix chain connected up to the "CE0" pin on your Pi Zero via the orange wire. Was this intentional?

Ombruz commented

Sorry, this is the connection diagram:
connections

I followed several guidelines about how to connect this kind of display on the raspi pinout.

Ombruz commented

You're great! I changed the order of wires this way:
DIN on MOSI pin
CLK on CE0
CS on SCLK
And I have the first success:
https://www.youtube.com/watch?v=aLpn27vG3r0&feature=youtu.be

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