Re: gEDA-user: OT - non-contact digital current loop sniffer

["David C. Kerber" <dkerber@xxxxxxxxxxxxxxxxxxxxxxxxxx>]

Yes, we have access to a single wire carrying the signal current (I remember enough of my 27-year old EE degree to catch that).  

But I had my doubts about a current transformer, because of the chance of having several bits at the same level, either high or low current, not giving any signal; ie a dc current for a short period, causing the signal from the CT to go to 0.  ISTM that this case would require some rather extensive signal processing, but I could easily be wrong about that; that's why I was thinking of a hall-effect transducer, which would detect dc signals.

Am I worrying about non-issues here?

Dave



> -----Original Message-----
> From: geda-user-bounces@xxxxxxxxxxxxxx 
> [mailto:geda-user-bounces@xxxxxxxxxxxxxx] On Behalf Of Andy Fierman
> Sent: Thursday, July 14, 2011 3:49 AM
> To: gEDA user mailing list
> Subject: Re: gEDA-user: OT - non-contact digital current loop sniffer
> 
> As long as you have access to a single wire and not the return path!
> 
> :)
> 
>          Andy.
> 
> signality.co.uk
> 
> 
> 
> 
> On 13 July 2011 22:48, Stephen Ecob 
> <silicon.on.inspiration@xxxxxxxxx> wrote:
> > On Thu, Jul 14, 2011 at 1:18 AM, David C. Kerber 
> > <dkerber@xxxxxxxxxxxxxxxxxxxxxxxxxx> wrote:
> >> Hi, electronics gurus -
> >>
> >> We have an application where we need to passively monitor 
> a digital current loop (no data sending by us), with a data 
> rate of 9600 baud.  We already have solutions for tapping 
> into the circuit, but in some of our customers' cases the 
> circuits don't have enough drive capability to add another 
> load to it.  So we're looking for a non-loading, and 
> preferably non-contact solution, such as a inductive pickup 
> or hall-effect pickup, that hopefully wouldn't require us to 
> break into the circuit.
> >>
> >> Does anybody know of such an animal?  If not, it's also 
> possible that we might contract to have one designed, but 
> that's not decided for sure yet.  It's a fairly electrically 
> noise environment, but not extreme, and the sensor itself 
> would likely be installed inside an already-existing box on 
> the wall.  The circuit runs at 45mA for the high signal, and 
> the low is <2mA.
> >
> > Is the current flowing through a length of accessible wire at some 
> > point, or is it only accessible in a PCB trace ?
> > If it flows through a length of wire then running it 
> through a current 
> > transformer could work well.
> >
> >
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> >
> 
> 
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