Data on 12V supply wires
in [Design]
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From: Jeff Johnson on 2 Aug 2010 20:49 "James" <nospamplease(a)nonsuch.com> wrote in message news:odaen1nxgwjk.1ppgdsfplxaie.dlg(a)40tude.net... > Hello, > > I want to send half duplex digital data - moderate rate, say 1k bps or a > bit faster - on a 12V, 2 wire, supply cable a few tens of metres long. It > is to connect a remote sensor to the user's display unit, both portable. > > The parts need to be fairly small (eg a chip and a few resistors). I was > hoping to be able to find a chip that will generate a modulated signal, > that could be connected to the supply cable. But I haven't been able to > find a chip that's designed for this. Please can anyone suggest anything? > > James If the load is not to large you can simply toggle the power line using a mosfet and filter afterwards. That is, a cap supplies temporary power to the device while the power line is off representing a change in state. As long as the data rate is fairly fast then it shouldn't be too much of a problem. The faster the better. This would require a mosfet, a cap, and a diode/mosfet for upstream only. Else it is more complex for bi-dir or downstream. Basically the device sending the data cuts it's power temporarily to signify a change in state. As long as the device has backup power then it will should surive. A long string of zero's of course might cause a problem and there are easy ways around this.
From: James on 4 Aug 2010 04:27 On Mon, 2 Aug 2010 10:13:28 +0100, James wrote: > Hello, > > I want to send half duplex digital data - moderate rate, say 1k bps or a > bit faster - on a 12V, 2 wire, supply cable a few tens of metres long. It > is to connect a remote sensor to the user's display unit, both portable. > > The parts need to be fairly small (eg a chip and a few resistors). I was > hoping to be able to find a chip that will generate a modulated signal, > that could be connected to the supply cable. But I haven't been able to > find a chip that's designed for this. Please can anyone suggest anything? > > James Thanks to all for ideas. I have put in a simple circuit to detect voltage pulsing of the supply line - by about half a volt or prehaps slightly more. Current pulsing at the sensor end. I don't know how it will be for noise immunity. If not good enough I will try adding a PLL later, looking at M-BUS and HART as well. James
From: JosephKK on 8 Aug 2010 17:50
On Mon, 2 Aug 2010 10:13:28 +0100, James <nospamplease(a)nonsuch.com> wrote: >Hello, > >I want to send half duplex digital data - moderate rate, say 1k bps or a >bit faster - on a 12V, 2 wire, supply cable a few tens of metres long. It >is to connect a remote sensor to the user's display unit, both portable. > >The parts need to be fairly small (eg a chip and a few resistors). I was >hoping to be able to find a chip that will generate a modulated signal, >that could be connected to the supply cable. But I haven't been able to >find a chip that's designed for this. Please can anyone suggest anything? > >James How about rethinking the requirement and use PoE, which has chips and other standard stuff. |