Electronics > Projects, Designs, and Technical Stuff
syncronise multiple ADCs over an Ethernet network?
nctnico:
--- Quote from: Yansi on December 12, 2019, 12:08:04 am ---
--- Quote from: nctnico on December 11, 2019, 08:59:40 pm ---
--- Quote from: FenTiger on December 08, 2019, 06:39:44 pm ---10kHz is one sample every 100us.
NTP might not reach that accuracy, but PTP (IEEE1588) will keep a pair of clocks synchronised much more closely than that over a single Ethernet hop.
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For PtP for work well you need to use fiber ethernet connections and you'll need special add-on hardware which can synchronise to PtP to get a reasonable accuracy. Also PtP will lose accuracy if you pump a lot of data over the network.
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No, unless you try to sync for timenut nonsense precision. .. which more then likely is not required here, neither for generic audio applications.
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The point is that PtP can be accurate but the achieved accuracy will depend on many IFs. If the system the OP wants to build is intended for a local installation then distributing time directly is a much more cost effective and reliable solution.
mansaxel:
--- Quote from: nctnico on December 11, 2019, 08:59:40 pm ---
For PtP for work well you need to use fiber ethernet connections and you'll need special add-on hardware which can synchronise to PtP to get a reasonable accuracy. Also PtP will lose accuracy if you pump a lot of data over the network.
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The medium is irrelevant, as long as it is a cable. I have lots of end nodes connected via copper, and they behave just nicely.
The special hardware, yes. The switch needs to be talking PTP, anything else is an invitation to headache. Network cards in end nodes also need to support PTP.
If you have PTP support in the switch and end nodes, you can go near flatline full on the link without much problems. If you do not prioritize or otherwise handle the PTP traffic as important (and having a switch that is boundary clock is, in my experience, by orders of magnitude the best way to do it.), you will have problems at everything above say 40% load.
Evan.Cornell:
--- Quote from: jbb on December 11, 2019, 10:30:42 am ---I think Analog Devices have a new series of “A2B” chips for distributing audio over twister pair in a car. Maybe some of that stuff could be repurposed?
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Un-obtainium for small guys.. they've got all the good info behind NDA-walls. I was looking at this for a multi-drop data acquisition system (several nodes to one main board via 10m cables), but ended up going with individual point-to-point SerDes links instead (DS90UA101-Q1 & DS90UA102-Q1 from TI).
Yansi:
Audio over twisted pair, like what? AES3? (AES/EBU aka professional SPDIF) - that's long known, no need for special chips for that.
DIT4192 and DIR9001 to the rescue. ^-^ (or any generic FPGA or even MCU these days)...
For multi-channel, there is the long known MADI over coax or SFP. Not a twisted pair, but certainly could be pushed throuch any kind of physical medium, including twisted pair. Note, that Soundcraft, those freaking bastards, use a RJ45 ports in between their mixing desks and stage boxes and call it "MADI". How the hell can one call that MADI? Especially, when there runs also some RS485/422 withing the same cable to control the stage box. Why, Soundcraft, why calling that MADI?!
GeorgeOfTheJungle:
If this is a dedicated network whose sole purpose is to control/communicate with these devices and not to download torrents and video streams from Netflix and youtube at the same time, I don't think he needs anymore than broadcast packets to synchronize/trigger the ADC conversions and a single UDP packet to transmit the samples back to the controller. IOW the clock signal are the broadcast packets. The smallest enet packet payload is fifty something bytes more than plenty enough to send a sample with a timestamp and more, back to the controller. Any switch can do that, even the cheapest ones are fast enough nowadays, and there won't be any dropped packets nor much jitter in a switched network that's being used well below the ports traffic limits.
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