I need to detect a DC current of about 0.3 - 0.4 mili-amps, but uncoupled.

[Chris]

Here is another possibility, where the opto section on the phone line
side doesn't require a power supply at all (and it loads the line
perhaps a little less than your example, even so) and where it is
possible to actually observe the line voltage by counting pulses. It's
a voltage to frequency converter. The other side of the opto will
require power, of course. Another difference is that the pulse
frequency would need to be handled:


I kept all the resistors of the same value, except for R5 which is
needed to help current limit at times, in case that helps any. I
think the frequency will vary roughly linearly with voltage, at about
10Hz/volt or so.

Jon

Rudy -- Forget the cobble I gave you -- this circuit is kewl. If you
feel you can handle the added complexity, go for it. I printed Jon's
circuit out, and I'm going to perf it up the next time I go to the lab
just to see it go.

I was actually considering offering you a relaxation oscillator using a
cap and a diac discharging through the opto, but they don't make 'em
like they used to -- minimum trigger voltage these days can be well
over your specified 30V.

Many thanks, Jon. You gave me a laugh -- elegant simplicity, sir.

Cheers
Chris

 

[R.Wieser]

Chris <[email protected]> schreef in berichtnieuws
[email protected]...

Hello Chris,

Rudy -- Forget the cobble I gave you -- this circuit is kewl. If you
feel you can handle the added complexity, go for it.

<snip>

Thanks for the thumbs-up.
It looks like I have no choice now than to *at least* try it.

Regards,
Rudy Wieser



I printed Jon's

 

[Jasen Betts]

Hello all,

I'm in the need to detect a phone-lines status, and the specs tell me that
I'm allowed to use the equivalent of a 80 KOhm resistor. In that case I
expect (hope) that the voltage of the line will stay at least 30 Volts,
which than results in a current of just 0.375 mili-amps.

Now the fun part : I need to detect the status while my electronics are not
DC-coupled to the phone-line (the lines should be able to float, while my
electronics should be able to connect to a computer, which will pull it to
ground-level (or close to it) ).

I thought about using an Opto-coupler. The problem is that I've only used
opto-couplers that use, in comparision with the above, massive ammounts of
current (5-30 mA). As I'm entering unknown territory I could use some
advice ....

A allso won't say "no" to a pointer to an allready existing design
Suggestions to do it another way are welcomed allso.

if it's a one-off take the isolating DC-DC convertor off an old 10-base-2
(coaxial) ethernet card and use that to provide current for the optocoupler.


Bye.
Jasen

 

[R.Wieser]

Jasen Betts <[email protected]> schreef in berichtnieuws
[email protected]...

Hello Jasen,

if it's a one-off take the isolating DC-DC convertor off an old 10-base-2
(coaxial) ethernet card and use that to provide current for the

optocoupler.

Although I would like to be able to replicate the design for the few people
that show intrest, your suggestion is a nice one, I'll have to keep it in
mind.

Regards,
Rudy Wieser

 

[Michael A. Terrell]

Funny : My previous message told you the same, only with a bit less ...
ranting in it


I'm sorry, did I miss something ?

Regards,
Rudy Wieser

Yeah, Phil thinks that he's a man.


--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida