phone line switch
Archiver
Posts: 46,084
I want to use my Basic Stamp II to switch my house phone line on and
off. Does anyone know what type of relay I will need? I don't know
phone line voltages and currents. I assume that I will need a 2 pole
relay as I use only the red and green phone wires. Thanks.
off. Does anyone know what type of relay I will need? I don't know
phone line voltages and currents. I assume that I will need a 2 pole
relay as I use only the red and green phone wires. Thanks.
Comments
wake you up if standing in the rain (and most likely even if it's not
wet in your location) when the phone rings. When your phone is not
picked up their is approx. 48 VDC on the line. When you pick up the
line an approx. 600 ohms is switched in to the circuit which all but
eliminates the DC, the phone company uses this signal to tell when you
have picked up your phone. And finally as you are talking on the phone
the actual AC voltage that represents your voice on the line is around
600 MV or .6 volt. This I believe is called 'line level'. I would
recommend you search out circuits that are specially made and UL
approved to connect to the phone. There are chips out their that do
this well. I have used a 600 ohm to 600 ohm transformer with a DPDT
switch or relay to work with limited results. Note: this IS NOT phone
company approved. Your design needs to take into account what happens
when all the above line conditions occur, especially the ring condition.
HTH,
Leroy
southernpost wrote:
>
> I want to use my Basic Stamp II to switch my house phone line on and
> off. Does anyone know what type of relay I will need? I don't know
> phone line voltages and currents. I assume that I will need a 2 pole
> relay as I use only the red and green phone wires. Thanks.
>
> To UNSUBSCRIBE, just send mail to:
> basicstamps-unsubscribe@yahoogroups.com
> from the same email address that you subscribed. Text in the Subject and Body
of the message will be ignored.
>
>
> Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
>I want to use my Basic Stamp II to switch my house phone line on and
>off. Does anyone know what type of relay I will need? I don't know
>phone line voltages and currents. I assume that I will need a 2 pole
>relay as I use only the red and green phone wires. Thanks.
First off, if this is for some sort of lightening protection, forget
it. If lightening comes in the line, it will jump the relay contacts as if
no gap is there. Induced voltages from nearby strikes not hitting the
lines directly will probably be stopped, but no guarantee even there. The
spark gaps in your connection block outside the home are supposed to shunt
the worst of a heavy strike, but something always gets thru and an open
relay isn't likely to stop it.
Assuming you just want to connect or disconnect your phone to/from the line
(control accessibility or ringing), you need a 2-pole relay to sit between
the red-to-red and green-to-green connections.
The max voltage *spec* is about 150 volts AC during ringing, but 40 - 90
VAC is more typical. Pretend it's 150 VAC when it comes to safety
considerations. On-hook voltage is 48 volts DC. Off-hook impedance is 600
ohms and voltage is "low" - meaning I don't know exactly, but it's easy
enough to measure if you want to know. Under all conditions, including
ringing, current isn't a significant consideration. A set of 500 ma
contacts with appropriate AC and DC voltage ratings should be more than
adequate.
Since you don't mention plans to connect any active devices to the line
other than type accepted phone equipment, I don't see any other
considerations practical, legal, or phone tariff related.
You could stop here unless you're interested in my continued rambling.
I'm wondering what you're really trying to achieve here. Cutting off the
main line kills everything, so calling parties get either a ringing
indication with no chance of an answer, or an out of service indication. I
don't know which, but I suspect the latter and that doesn't seem
desirable. A line to an answering machine bypassing the relay to the
line(s) to all phones sounds better to me, but it's your thing.
Some phone companies used to "scan" their subscriber lines looking for
"proper" on-hook impedance and automatically log a service problem if a
"nothing there" indication was found. At that point you could find
yourself logged out of service and it could take a while, maybe 30 minutes
and maybe much longer, to reacquire dial tone after reconnecting your phone
to the line. That's probably an all but obsolete practice, and even so
modern digital switches are probably quicker to handle return of dial
tone. But be aware of this possibility and maybe check to see how long it
takes to get a dial tone after reconnecting following a long
disconnection. If I were to call my telco and ask about this I think
they'd just say "huh?" You might be luckier.
Good luck. And if you (or anyone) figure out how to zap the telemarketers,
let me know. The SOBs pay the telcos to broadcast a caller ID that
contains no info, but isn't "blocked," so my CID device (commercial device,
not Stamp device) can't filter them on any criteria that doesn't also zap
friends whose really old crossbar or old digital switch exchanges originate
no CID info. Lately they're taken to leaving robotic recorded messages on
my answering machine. I'm going to have to try changing my voice
announcement to start with a SIT tone - that three-tone sound that
indicates a problem that prevents connection. The so-called ZAPPER claims
to work on that principle and that the telemarketer's autodialers log the
number as not working and never call again. My best guess is that
telemarketer's machines aren't set to pay it any attention and it's really
worthless. Anyone know for sure?
Jim H
what and why I am doing:
I want to disconnect the phone of my girl friends 15 year old
daughter at a certain time each night as we seem to be unable to stop
her friends from calling the house at all hours of the night.
I can disconnect her phone as well as our bedroom phone but leave
other phones connected which won't wake us up. I want to automate the
process so that I don't have to run around turning ringers off every
night as well as to prevent her from simply turning the phone back on.
I have the real-time clock chip and crystal but need to appropriate
relay. I am an experienced computer programmer but am just learning
the electronics part.
The voltage and current details which you gave are great. Do you know
of any sources for the type of relay that I need?
Thanks again.
Scott
switch it one way or the other. This way you would not have to supply power
to the relay coil constantly and could let the Stamp sleep or do other
things. Most of the older phones and modems that had relays used the small
ones that fit in a 14- or 16-pin IC socket.
Keep in mind some latching relays require you to reverse the coil connection
to unlatch it -- this is a bigger pain than its worth.
***********
> I want to disconnect the phone of my girl friends 15 year old
> daughter at a certain time each night as we seem to be unable to stop
> her friends from calling the house at all hours of the night.
>
> I can disconnect her phone as well as our bedroom phone but leave
> other phones connected which won't wake us up. I want to automate the
> process so that I don't have to run around turning ringers off every
> night as well as to prevent her from simply turning the phone back on.
>
> I have the real-time clock chip and crystal but need to appropriate
> relay. I am an experienced computer programmer but am just learning
> the electronics part.
>
> The voltage and current details which you gave are great. Do you know
> of any sources for the type of relay that I need?
>it. If lightening comes in the line, it will jump the relay contacts as if
>no gap is there. Induced voltages from nearby strikes not hitting the
>lines directly will probably be stopped, but no guarantee even there. The
>spark gaps in your connection block outside the home are supposed to shunt
>the worst of a heavy strike, but something always gets thru and an open
>relay isn't likely to stop it.
Hi Jim,
While no guarantee, I do think that relays can provide significant
protection. After all, very few hits are direct, and a relay with an
isolation rating of 1000 volts coupled with the telco spark arresters
and some heavy transorbs can divert moderate induced ESD surges.
We had about 80 stations along the lightning prone gulf coast
configured to dial out to a central computer (BBS text-based system)
once each per day. They only connected to the phone line during the
few minutes it took them to upload the accumulated data. At first
we did not have the relay and suffered losses, but after the relay it
became a non-issue. Those were DIP type DPST relays that only needed
to be closed for a couple of minutes a day.
I don't think the phone company does much testing these days for
ringer equivalence on lines. Most modern equipment has a ringer
equivalence somewhere near zero. I recall that the voltage on the
line when off hook drops to about 6 volts DC.
I can sympathize with Scott's dilemma. No too long ago I had 3
teenagers at home at once, and I refused to get extra phone lines.
(No disrespect meant to the teens on this list!) Maybe phone-line
control would be a good stampsinclass project?
-- Tracy
Good info on your direct experience with relay line isolation! I've not
had much luck with cheap no-name phones and nearby lightening strikes when
I had above ground wiring, but the AT&T cordless kept on ticking. I wasn't
using isolation however.
>I can sympathize with Scott's dilemma. No too long ago I had 3
>teenagers at home at once, and I refused to get extra phone lines.
>(No disrespect meant to the teens on this list!) Maybe phone-line
>control would be a good stampsinclass project?
It sure could be for some - esp if it integrated - in modular fashion -
CID, incoming and outgoing blocking of certain area codes (900 and
Caribbean for example) or specific numbers, or during specific hours; i.e,
enforcement of "You're grounded and no phone!" during the hours the subject
might be home alone.
But in closing... admit it now... you did smile to yourself when you heard
the teenagers fuss at each other to get off the line, didn't you? Was the
sensation of hearing that perhaps akin to the delicious irony of hearing
the crunch of metal while driving and stopping to find that, as long as
there had to be a wreck, at least it's two drunks that have hit each
other? (Even better if they get out and start fighting!)
Jim H
>Thanks Jim. You bring up some good points. A little more detail on
>what and why I am doing:
>
>I want to disconnect the phone of my girl friends 15 year old
>daughter at a certain time each night as we seem to be unable to stop
>her friends from calling the house at all hours of the night.
>
>I can disconnect her phone as well as our bedroom phone but leave
>other phones connected which won't wake us up. I want to automate the
>process so that I don't have to run around turning ringers off every
>night as well as to prevent her from simply turning the phone back on.
>
>I have the real-time clock chip and crystal but need to appropriate
>relay. I am an experienced computer programmer but am just learning
>the electronics part.
>
>The voltage and current details which you gave are great. Do you know
>of any sources for the type of relay that I need?
I bet Radio Shack has what you need. Since you're not looking for
isolation from lightening most anything will do as long as it's at least
double pole. Just pay attention to the coil voltage and coil current
requirements so you can use something like one of the cheaper standard wall
wart power supplies most of us have several of laying around.
I'm guessing a stealth location is needed for the device and that its
existence is to be a secret, otherwise the hunt for it could be on. If so,
then leaving at least an answering machine connected seems to be necessary
so friends don't report an "out of service message" when they call. I'm
still assuming that's the result from absolutely zero load on the line. If
I had a cell phone, I'd unplug all my home phones and call myself, but I
don't have one.
And not to spoil your Stamp fun, but one of those cheap 24-hour timers that
turns lamps off and on connected to a 110 VAC double pole relay would be a
lot cheaper than the Stamp + clock chip solution. Settability wouldn't be
as precise, but probably good enough. And these devices don't gain or lose
time any more than AC powered clocks do - meaning it usually takes a power
outage to get them out of synch with real time.
Jim H