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FM Transmitter issue

Started by Kensington Graves, November 25, 2022, 07:16:41 AM

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Kensington Graves

I came acros an odd problem last night while trying to deploy a Signstek ST-05B on my master FPP.  Heretofore, I used the VAST FMT-212 without issue.

My setup: FPP 5.4.1 running on a BBB with a SB Play! USB soundboard.  I know. I should upgrade FPP.  I haven't wanted to mess with anything while getting the kinks worked out this year.

FPP recognizes the Soundblaster.  The Soundblaster tests good—it drives a directly attached speaker when a sequence is played.

When the VAST transmitter is reconnected, it works fine.

Symptoms of the problem.

0. Si473/VAST FMT212 plugin is installed.  I don't think this is relevant, but I mention it just in case.

1. If the Signstek transmitter is attached to the SB Play! and is powered on when FPP boots, no sound device is detected.  Either "Dummy" or no devices at all appear in the drop-down box.

2.  If the Signstek transmitter is connected to the SB Play! and is powered off when FPP boots, the SB Play! Is detected.

3.  In case 2, if the Signstek is powered on after boot, the audio device field is wiped clear and no sound device appears in the drop down box under audio/video settings.  I also get an error message of "Could not open audio device - ALSA: Could not open audio device: No such file or directory.

I've posted screen shots of the status page with the error message, and the audio/video tab.

The Apache2-error.log shows:

Thu Nov 24 20:25:18.507712 2022] [php7:notice] [pid 19236] [client] Error getting mixer devices!
[Thu Nov 24 20:37:59.929933 2022] [php7:notice] [pid 2348] [client] Error getting mixer devices!
[Thu Nov 24 20:44:27.870599 2022] [php7:notice] [pid 2775] [client] Error getting mixer devices!
[Thu Nov 24 20:48:16.759941 2022] [php7:notice] [pid 1576] [client] Error getting mixer devices!

fppd.log shows nothing unusual.  Just messages related to multi sync and scheduler. 

I suspect that there is some backfeed along the audio input line from the transmitter when it powers on/is on, and that is causing the USB device to reset.  Any thoughts?


Had the same problem. Had to move my transmitter further away from the SB ( 6' in my case). 

Kensington Graves

Interesting.  Mine is on a 1.5m audio cable.  I'll order a 2m cable and see if that helps.  Thanks, Rudybuddy.


You might also want to check the transmit power setting, if it's on high (I believe default) will also cause a problem with the SB. The low power setting will allow it to be closer to the SB and still provide plenty of range for your show.

Kensington Graves

The longer cable did the trick.  Thanks again.


Useful to know that the SoundBlaster is that RF sensitive.  I am using a SoundBlaster 3 for my show audio (plugged into a PC, not a FPP instance), but it's about 100 feet from the transmitter.

BTW, you pretty much can't just plug in a 100 foot cable from an audio source to the transmitter and get good audio.  If you need to do something like that, ask me how...  Radio broadcast engineer background comes in handy once in a while.
Using LOR (mostly SuperStar) for all sequencing - using FPP only to drive P5 and P10 panels.
My show website:


Kensington Graves

I will cheerfully endure your critique of my system if you make it out my way this year.

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