Scroll pHat HD - "pixelation" problems

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1

I’ve got a Scroll pHat HD on a Raspberry Pi Zero W with a Button Shim sandwiched between it and the Pi. The Scroll pHat HD and the Button Shim were added to the female header with the Hammer Header.

I’ve installed the libraries and examples via:

curl -sS https://get.pimoroni.com/scrollphathd | bash

Both the Scroll pHat HD and the Button Shim appear to be available:

i2cdetect -y 1

     0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f
00:          -- -- -- -- -- -- -- -- -- -- -- -- -- 
10: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
20: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
30: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 3f 
40: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
50: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
60: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
70: -- -- -- -- 74 -- -- --                         

uname -a

Linux raspberrypi 4.9.35+ #1014 Fri Jun 30 14:34:49 BST 2017 armv6l GNU/Linux

lsb_release -a

No LSB modules are available.
Distributor ID:	Raspbian
Description:	Raspbian GNU/Linux 8.0 (jessie)
Release:	8.0
Codename:	jessie

However, when I run any of the example python scripts, there appears to be “pixelation” or “interference” with seemingly constant random LEDs switching on or off. The Button Shim is working as expected. This is my second Scroll pHat HD where this has occurred, I put the issue with the first one down to my soldering. I’ve tried this on another Pi Zero, albeit with the same SD card, so it’s quite possibly a system configuration issue on this card. It is running off the official Raspberry Pi power supply.

The photos show the output from the examples/tests directory (with a diffuser cover), i.e. the Scroll pHat HD is supposed to be showing the text 1234.

python transform-test.py -m 1234

DSC_0242
DSC_0242.JPG1948×1032 772 KB

DSC_0246
DSC_0247

I created this test script - for every loop of brightness, the display changes with seemingly random incorrect LEDs light.

import time
import scrollphathd
from scrollphathd.fonts import font5x7


def do_test(text):
    for bright in [0.1, 0.25, 0.4, 0.55, 0.7]:
        scrollphathd.clear()
        scrollphathd.write_string(text, font=font5x7, brightness=bright)
        scrollphathd.show()
        time.sleep(0.75)

for test in range(3):
    for chars in ['ABC', 'DEF', 'GHI', 'JKL', 'MNO', 'PQR' ,'STU',
                  'VWX' ,'YZ0', '123', '456', '789', '!#?', '<>*']:
        print chars        
        do_test(chars)

Not sure if this is similar to the “flickering” report in https://github.com/pimoroni/scroll-phat-hd/issues/33. I’ve ran the bash script from user jose1711 from this GitHub issue, but it also shows incorrect LEDs being displayed.

Any ideas?

2

Is the Scroll pHAT HD robustly attached to the hammer header? They aren’t really designed to be used with a SHIM and a pHAT at the same time, so I suspect that the Scroll pHAT HD isn’t making a stable electrical contact with the header?

The code you posted worked fine for me, so that’s not an issue.

Any chance you could take the diffuser off and take a photo from the side to see how the header looks?

1 Like
3

Here’s a close-up with the diffuser off.

DSC_0252
DSC_0252.JPG2532×976 1.13 MB