Unicorn Hat not lighting up at all

I just got my Unicorn Hat (PIM054) and installed it on a Raspberry Pi3B+. Everything on the pi is up to date. I ran several examples after the installation and nothing happens, none of the leds turn on at all on the UnicornHat. Examples run without errors.

Ran as sudo? I do believe for some strange reason you have to use sudo?
Firmly attached to the Pi’s GPIO?

Hi alfanumeric,
I am running the examples using sudo, checked the good attachment to the PI, still do not see any led lighting up.
Any ideas?

Nothing comes to mind? I have two Unicorn HD’s and an HD Mini. I get error messages if for example SPI isn’t enabled. Or I’m missing a required font etc. I have yet to get no LED’s lit without some kind of error message as a hint to what’s wrong.
Anything else attached to that Pi? If you have ever had other things attached and installed software for them, I recommend starting over with a clean PiOS image.

Thanks alphanumeric. I have rebooted the PI with a clean OS without luck but I have found a quick workaround. I have downgraded the piOS from the latest to a previous 2020 release: https://downloads.raspberrypi.org/raspbian/images/raspbian-2020-02-14/
and the unicorn Hat is now working as expected.

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Nice to hear you found a solution. I have resorted to older builds in the past to confirm something in the latest and greatest broke something that worked before.
My Unicorn Hat HD’s work OK in the latest 2020-12-02. I don’t think I’ve tried my Unicorn Mini’s with that build yet though?

I had a similar problem where only two lights would light up - on (a fresh install of) the default raspbian package available today in the Raspberry Pi Imager. I installed the light version of the raspbian from 2020-02-14 linked by oeolartep and now it works fine. That said, I also said “NO” to the install script for unicorn hat making changes to my audio, as I was also previously getting no audio out of my headphone out. Now, both the unicorn hat and audio out are working (haven’t tried simultaneously - guessing that won’t work)!

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I suspect GPIO 18 may be used for i2s. I would think saying yes or no would have no effect on the onboard HDMI or jack out audio. Might mess up a hat with a DAC on it though. Just my best guess really.

Thanks evilunix - I’ve lost several hours today trying to get my Unicorn HAT working with buster desktop version until I found your note. I knew it wasn’t the Pi or HAT at fault as going back to an old SD with raspbian on made everything worked fine as oeolartep said.

The current download of “Raspberry Pi OS Lite” followed by update everything and install unicornhat by curl and all works well. However with the current “Raspberry Pi OS with desktop” all I get is the two LEDs flashing in one corner. Obviously something in the desktop breaks the unicornhat.

I even tried the latest nightly build of desktop and it breaks too.

I’ll try and report this as a bug on the github page as the solution to this thread “go back to raspbian” isn’t really a solution and nor is “don’t use the desktop”.

Just FYI post, you can get any and all of the official images here,
Index of /raspbian/images (raspberrypi.org)

If you don’t have an older card on hand this will bail you out.