Raspberry Pi STL in a Box

I promised more details in the future about the Raspberry Pi STL build. Well, against all odds, I’m going to deliver!

The project exists purely to solve a problem with getting audio between two sites for a hospital radio station. They currently use a costly dedicated line that’s purely analogue. Imagine the old fashioned exchange with patch cables everywhere and you’ve pretty much got the picture. Ok, I admit it’s not quite that old fashioned, but a balanced line with “Post Office” written on the equipment doesn’t really scream the height of modern technology.

Raspberry Pi STL in a Box

To reduce costs and improve quality, we started looked at a number of other options. RF links of any form are pretty much a dead option thanks to the terrain between the two sites. It might only be three miles between them as the crow flies but there’s a ridge in the way. There’s no way we’re getting anything near “line of site” between them.

That’s pushed us to look at IP and ADSL circuits. We’re planning to get one installed which this box will be plumbed in to.

And talking of the box, it’s configured to pull a private webstream and fallback to an audio loop on failure. This is something a Raspberry Pi can do with little bother and detailed in this article about configuring LiquidSoap (the software we’re using). LiquidSoap and webstreaming was chosen over OpenOB as the station is already generating a private stream in 64k AAC+ and we needed the fallback feature.

But that doesn’t explain why I’ve gutted an old equipment box headed for the bin rather than just directly installing the Raspberry Pi. There’s two reasons for that. Firstly, we need the audio output to be electrically balanced. While something like an Alice Matchpak could have been used, it’s yet another box that has to be supported in a remote location.

Raspberry Pi STL in a Box SChematicThe second reason I’ve built this box is that it’s going into a remote location the station has limited access to (someone else’s racks room). Simple metering and a 16×2 LCD display provide information that can be relayed to us over the phone if something goes wrong. I doubt many engineers will struggle to understand a display that says “!!!ON BACKUP!!!” along with “No IP Address!”.


For more detail: Raspberry Pi STL in a Box

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