mgrant@cos.com (Michael Grant) (10/01/88)
A long while ago someone posted a question about how to build a simple
circuit which would light a LED (or a simple lamp) when an extension
was lifted elsewhere in the house. The requirements are:
- The LED lights when another extension is lifted, showing that it
is in use.
- The LED must be powered off the phone line.
- No extra wires must be run to the telephone.
- The circuit should be reasonable small so that it can fit inside a
desktop style phone.
No one was able to come up with a simple schematic to do this that
worked. The upshot was that one could buy such a device for about $30
off the shelf. Having let some time pass, anyone want to give a stab
at this?
-Michael Grantmgrant@cos.com (Michael Grant) (10/05/88)
For $24.95, Hello-Direct makes a device called the "Privacy Device" on
Page 8 of their Fall catalog. It has an annoying "feature" though...
"Make sure no one is listening in on your calls."
"You're assured of privacy when the Silent Patrol is on duty on
your single-line telephone. Just plug it in between your phone and
the wall and it will let you know any time someone is listening in on
an extension or tapping your line. In the event of either of these
invasions of your privacy your line will go dead and an LED will give
you a visual warning. Just press an over-ride button if you want to
resume your conversation without clearing the line. An On/Off switch
lets you activate/deactivate the device."
Part No. 1039-A
Hello-Direct's number is: 1-800-444-3556 in the USA.
I am not associated with Hello Direct in any way.
-Mike Grant
p.s. There's got to be an easy way to build something similar.pozar@toad.com (Tim Pozar) (10/10/88)
{{{ Quoted text edited down to make inews happy. -CR }}}
mgrant@cos.com (Michael Grant) wrote:
> For $24.95, Hello-Direct makes a device called the "Privacy Device" on
> Page 8 of their Fall catalog. It has an annoying "feature" though...
>
> "Make sure no one is listening in on your calls."
This device will not work for a proper phone tap. If some
one bridges across your lines with a high impeadence phone
tap, these devices will not notice the change in current or
impeadence.
Timsteves@tekgen.bv.tek.com (Steve Shellans) (10/11/88)
In article <telecom-v08i0153m04@vector.UUCP> mgrant@cos.com (Michael Grant) writes: >X-Administrivia-To: telecom-request@vector.uucp (USENET Telecom Moderator) > >For $24.95, Hello-Direct makes a device called the "Privacy Device" on >Page 8 of their Fall catalog. It has an annoying "feature" though... > > "Make sure no one is listening in on your calls." > > "You're assured of privacy when the Silent Patrol is on duty on > your single-line telephone. Just plug it in between your phone and > the wall and it will let you know any time someone is listening in on I can readily understand how one of these devices would work if someone clips on a low-impedence handset (or phone) on your line. You can usually hear a drop in volume when someone picks up an extension phone, and this condition should be pretty easy to detect electronically. But suppose someone has a very high-impedence input to an amplifier, puts this across your line, and then just amplifies the signal as necessary. Can these privacy devices detect this situation, and if so, how? Steve Shellans Tektronix, Beaverton OR steves@tekgen.BV.TEK.COM
aem@umbio.MIAMI.EDU (A. Mossberg) (10/11/88)
Mike said: >I might even be willing to let $30 for such a device (maybe). Where is >one available? There's a device in the most recent DAK catalogue (I don't have it handy, but you can call 800 information for their number) which looks like a standard rj-11 y-connector, but with 2 leds on top. One jack is a priority jack, lifting anything on that line will kill anything on the other, and the other is blocked if the priority circuit is in use. I believe it was under $15 for this unit. They're primarily selling it for use with answering machines (pick up the phone, machine is disconnected from line) but mention these other uses.. (I's just a customer, no kickbacks here!) aem -- a.e.mossberg - aem@mthvax.miami.edu - aem@mthvax.span (3.91) Why, sometimes I've believed as many as six impossible things before breakfast. - Lewis Carroll
sleat@ardent.UUCP (Michael Sleator) (10/14/88)
In article <telecom-v08i0150m11@vector.UUCP> jetzer@studsys.mu.edu (jetzer) writes: [discussion of indicator light to show phone off hook] >I would also be interested in such a device - my roommate has this >nasty habit of picking up the phone while I'm using my modem. Seems to me that maybe what you need is an "exclusion circuit". You can buy these (from Radio Smack?) or make one with an SCR, a Zener diode, and a resistor. It works as follows: The circuit is put in series with a phone or modem. If the line is in the on-hook state and the phone goes off-hook, the phone is connected as normal. However, if the line is already off-hook, then the phone is completely dead. As a side effect (at least with the circuit I use), if the line is off-hook and the phone is taken off-hook, and then the other load that was holding the line off-hook goes on-hook, the previously dead phone gets the line before it goes on-hook. (If you can follow that description...) Thus, hanging up the phone that was on the line immediately transfers the line to the waiting phone without dropping the call. I also tend to put a bypass switch on a phone when I install one of these, so that if I deliberately want to break in, I can. I put these things on phones and modems whenever they share a line so that people don't trash the data and so that when uucp fires up it doesn't blast people off the line. Works like a charm. Michael Sleator Ardent Computer ...!{decwrl | hplabs | ubvax | uunet}!ardent!sleat
sleat@ardent.UUCP (Michael Sleator) (10/15/88)
In article <telecom-v08i0153m04@vector.UUCP> mgrant@cos.com (Michael Grant) writes: >For $24.95, Hello-Direct makes a device called the "Privacy Device" on >Page 8 of their Fall catalog. It has an annoying "feature" though... > > "Make sure no one is listening in on your calls." > > "You're assured of privacy when the Silent Patrol is on duty on > your single-line telephone. Just plug it in between your phone and > the wall and it will let you know any time someone is listening in on > an extension or tapping your line. In the event of either of these [etc.] ^^^^^^^^^^^^^^^^^ don't believe it! I hate advertising hype, so I just wanted to correct this. Sure, you can build a device that detects another load such as a phone, but anyone who knows anything about electronics can tap a subscriber loop in such a way that nothing will be able to distinguish the minute effect of the tap from normal effects. (Hint: imagine clamping an oscilloscope current probe around one of the conductors.) Anyone who tries to sell you something with the claim that it will detect "any" tapping on the line is most likely lying. Michael Sleator Ardent Computer ...!{decwrl | hplabs | ubvax | uunet}!ardent!sleat
dave@uunet.UU.NET (Dave Horsfall) (10/18/88)
In article <telecom-v08i0148m08@vector.UUCP>, mgrant@cos.com (Michael Grant) writes: [ An "in-use" LED for a telephone extension ] A local electronics hobbyist magazine "Silicon Chip" published such a circuit, involving monitoring the line voltage and triggering an LM3909 LED flasher when it drops to around 12v or so. There was also a companion circuit, which blocked other extensions when one was picked up - useful! This worked on a similar principle, and it fires an SCR across each extension instead. The device has gone a long way to keeping my wife off the phone when I'm on the modem... I see no reason why an Australian design should not work elsewhere; they merely compared the line voltage (50v on-hook) against a reference zener, and did its magic when it dropped (about 12v off-hook). A diode bridge supplied the power, and the LM3909 is quite an efficient flasher. The diagrams won't reproduce too well on a terminal screen, so I'll send photocopies of the articles to anyone who wants them, although I'd prefer not to be inundated... Perhaps the first few enquirers (assuming there are any :-) can supply others in their country. Oh, and Telecom get stroppy when they find you connecting non-approved devices to their network, so y'all are warned. -- Dave Horsfall (VK2KFU), Alcatel-STC Australia, dave@stcns3.stc.oz dave%stcns3.stc.OZ.AU@uunet.UU.NET, ...munnari!stcns3.stc.OZ.AU!dave PCs haven't changed computing history - merely repeated it
dave@uunet.UU.NET (Dave Horsfall) (12/05/88)
Some time ago, mgrant@cos.com wanted a circuit for an "in-use" indicator
for a telephone extension, and I offered to send a copy of a circuit to
anyone interested.
Well, here are the people I sent the circuit to, in case you want to
contact them:
Steve Lemke
steve@ivucsb.UUCP; lemke@apple.COM; pyramid!comdesign!ivucsb!steve
Jerry Glomph Black
black%micro@ll-vlsi.arpa
Michael Grant
mgrant@cos.com
I see that Michael took the trouble to type up the circuit in ASCII
form - phew!
I hope you find the circuit of use - it works for me.
--
Dave Horsfall (VK2KFU), Alcatel-STC Australia, dave@stcns3.stc.oz
dave%stcns3.stc.oz.AU@uunet.UU.NET, ...munnari!stcns3.stc.oz.AU!dave
PCs haven't changed computing history - merely repeated it