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Neopixel Ring doesn't correctly light with no HDMI
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Neopixel Ring doesn't correctly light with no HDMI

by sambenge on Wed Sep 14, 2016 4:06 pm

Hey,

I currently have a Neopixel 24 Ring connected to a Raspberry Pi using the rpi_ws281x library following this tutorial https://learn.adafruit.com/neopixels-on-raspberry-pi/software. It works perfectly when I have HDMI connected to my monitor, but the ring doesn't light correctly when there is no monitor connected. It appears to somewhat light the lights individually in RGB (as in the first light is red, the second is green), but this pattern isn't consistent and a section of the lights (grouped together, I believe the last 8 lights) unpredictably strobe. This is only when HDMI isn't connected though, as when a HDMI monitor is connected, everything works perfectly.

Unfortunately, I can't have a HDMI monitor connected to my Pi for it's use, so this really isn't ideal. However, it works perfectly on my 1080p monitor directly from HDMI, but didn't work correctly when connected to a lower resolution monitor connected with DVI, so I'm not sure whether this is due to the HDMI to DVI connection or the resolution. Regretably I don't have access to the HDMI to DVI cable anymore so I can't test more with this.

Is this a known issue, and if so is there a fix? The only thing I can think of is to try and trick the Pi into thinking it's connected to a monitor using HDMI, presumably using the config.txt file, but I wanted to check if this was a known issue before messing with that file. I've tried connecting a HDMI cable without a monitor attached, but this doesn't fix the issue.

Thank you for your help,
Sam

sambenge
 
Posts: 6
Joined: Sat Jul 02, 2016 12:36 pm

Re: Neopixel Ring doesn't correctly light with no HDMI

by avanderspek on Sun Feb 11, 2018 5:28 pm

Hi sambenge
I'm getting that sane symptom with a project I'm working on now. It only works with HDMI monitor plugged in. Did you discover a solution?

avanderspek
 
Posts: 2
Joined: Sun Feb 11, 2018 5:26 pm

Re: Neopixel Ring doesn't correctly light with no HDMI

by avanderspek on Sun Feb 11, 2018 5:53 pm

Fixed! The neopixel driver and default audio driver conflict over use of PWM. When an HDMI monitor is plugged in, the HDMI audio driver is used instead. I worked around it by adding:
hdmi_force_hotplug=1
hdmi_force_edid_audio=1
to /boot/config.txt

avanderspek
 
Posts: 2
Joined: Sun Feb 11, 2018 5:26 pm

Re: Neopixel Ring doesn't correctly light with no HDMI

by sambenge on Mon Feb 12, 2018 12:09 pm

Yeah, that looks like the solution I used too!

Glad you managed to find it, and good luck with the rest of your project.

sambenge
 
Posts: 6
Joined: Sat Jul 02, 2016 12:36 pm

Please be positive and constructive with your questions and comments.