[asterisk-users] RS485 Audio device

Pete Mundy pete at fiberphone.co.nz
Wed Nov 2 14:24:24 CDT 2016

It caught my interest for the same reason! It's such an obscure query.

My guess was that the desire was to run it over an existing shared RS485 bus, which means the maximum data rate available would be even less because it would be shared with other devices.

The only way I could imagine a solution working in this scenario would be some sort of ATA attached to a router which supported PPP and had an RS232 serial port on the WAN side (eg like an old modem router), which could then be converted into RS485. You could possibly do all that in a Raspberry Pi with a USB-RS232 adapter (or even a USB-RS485 adapter directly!). Then you'd run SIP over IP over PPP to a similar device on the other end of the bus. But you'd obviously have to be sure to use a low bandwidth codec, and you'd possibly suffer audio quality issues when there was (RS485) bus contention.

But that was all guess work. It would be great if OP Jerry could expand a little more on the application scenario, even if just to whet the curious appetites :)


> On 3/11/2016, at 3:48 am, Telium Technical Support <support at telium.ca> wrote:
> This one caught my interest too...more out of curiosity!  Keep in mind that
> RS485 max speed drops to 100kbps after a relatively short distance.  And,
> 100kbps is RAW speed.  If you encapsulated your audio stream in that you'd
> lose another 10%.
> So why are you doing this?  If you are running a 100m cable (4 wire +
> shield) why not just pull at cat5/6 cable instead?  Or just send analog
> audio over 2 of the wires with the shield to keep out hum.   If there is a
> need to use rs485 you could stream your audio over that connection - but I'm
> curious why first.
> We did some work for broadcast (radio station) doing AoIP and converting
> some analog feeds but this seems unusual.
> Jason

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