Does anyone have plans for a simple off-hook detector? I need to know when someone has lifted a receiver. A dial-tone detector circuit would also work.
I don't know where this started, so I might be redundent with my comments.
1. The phone company puts appx. 50 volts on your line, through the equivalent of about 1000 ohms in series. If your phone is 'on hook', a normal Voltmeter will read that 50 volts. 2. When you take your phone 'off hook', the voltage will drop. How much? Depends on the phone. I have seen readings of 7 to 26 VDc. If another extention phone goes 'off hook', the voltage will drop a bit lower.
A 28 VDC, 5 K ohm relay wired directlt across the telephone line will normally drop out when a phone goes 'off hook', while not loading the line too badly. I made a telephone recorder activation circuit this way, and added 200 or so turns arould the coil to pick off the audio. Worked first time!
Hello! I missed the original post, but in addition to the other comments, I thought I'd mention that in *most* residential lines, the phone company's Central Office (CO) detects a Off-Hook condition when a small current is drawn on the line. This is known as "Loop Start". the alternative, mainly used in larger PBX's (Private Branch Exchange, I.E. Company phone system) is "Ground Start" where the CO equipment detects a momentary ground on the line as an off-hook condition. SAM'S has an excellent book in their "Understanding" Series (Title:Understanding Telephone Electronics) that is well worth eading if you'd like to get into telephone devices/accessories. Radio Shack also carries a book on telephone electronics. Incidentally, the "On-Hook" voltage of a standard phone line is 48VDC by spec, although this can vary depending on distance from your local CO, Etc. a typical Single-Line phone has an off-Hook resistance of Approx. 400 Ohms this provides a 120ma draw on the 48V line, which is limited to Typically 15ma. this is what causes the drop in voltage to approx 5-10VDC when a phone goes off-Hook (15ma * 400 Ohms = 6V) the variance is caused by the fact that the CO has a lot of slop in their current-Limiting :-) I seem to remember that they are required by law to limit it to less than 150ma, which leaves them a LOT of room. I hope this proves helpfull Robb Hammack
Edward Lawrence (eal) penned: : I don't know where this started, so I might be redundent with my comments.
: 1. The phone company puts appx. 50 volts on your line, through the : equivalent of about 1000 ohms in series. If your phone is 'on hook', a normal : Voltmeter will read that 50 volts. : 2. When you take your phone 'off hook', the voltage will drop. How : much? Depends on the phone. I have seen readings of 7 to 26 VDc. If another : extention phone goes 'off hook', the voltage will drop a bit lower.
: A 28 VDC, 5 K ohm relay wired directlt across the telephone line will : normally drop out when a phone goes 'off hook', while not loading the line too : badly. I made a telephone recorder activation circuit this way, and added 200 : or so turns arould the coil to pick off the audio. Worked first time!
That's way too much load on the line IHMO. The ampunt of current drawn by the relay during the on hook is way too high: several milliamps! The CO may measure this and determine that there is too much leakage current and try to repair the lines. This could cost you the service call if they find that the problem is in the CPE (customer provided eauipment). Or the current could cause the switch to think that the phone was off hook all the time, and then it would disable the line.
: Hope this helps.
-- #======P=G=P==k=e=y==a=v=a=i=l=a=b=l=e==u=p=o=n==r=e=q=u=e=s=t======# | John Lundgren - Elec Tech - Info Tech Svcs. | jlundgre@delta1 | | Rancho Santiago Community College District | .deltanet.com | | 17th St at Bristol \ Santa Ana, CA 92706 | http://rsc.rancho| | My opinions are my own, and not my employer's. | .cc.ca.us | | Most FAQs are available through Thomas Fine's WWW FAQ archive: | |http://www.cis.ohio-state.edu:80/hypertext/faq/usenet/FAQ-List.html| | "You can flame your brains out -- it won't take long." | #===T=u=z=l=a==C=o=m=p=a=n=y=.=.===t=h=r=e=e='=s==L=e==C=r=o=w=d=!==#
Robb Hammack (104056.2...@CompuServe.COM) penned: : Hello! I missed the original post, but in addition to the other : comments, I thought I'd mention that in *most* residential lines, : the phone company's Central Office (CO) detects a Off-Hook : condition when a small current is drawn on the line. This is known : as "Loop Start". the alternative, mainly used in larger PBX's : (Private Branch Exchange, I.E. Company phone system) is "Ground : Start" where the CO equipment detects a momentary ground on the : line as an off-hook condition. SAM'S has an excellent book in : their "Understanding" Series (Title:Understanding Telephone : Electronics) that is well worth eading if you'd like to get into : telephone devices/accessories. Radio Shack also carries a book on : telephone electronics. Incidentally, the "On-Hook" voltage of a : standard phone line is 48VDC by spec, although this can vary : depending on distance from your local CO, Etc. a typical : Single-Line phone has an off-Hook resistance of Approx. 400 Ohms : this provides a 120ma draw on the 48V line, which is limited to : Typically 15ma. this is what causes the drop in voltage to approx : 5-10VDC when a phone goes off-Hook (15ma * 400 Ohms = 6V) the : variance is caused by the fact that the CO has a lot of slop in : their current-Limiting :-) I seem to remember that they are : required by law to limit it to less than 150ma, which leaves them : a LOT of room. : I hope this proves helpfull : Robb Hammack
The phone line should supply a minimum of 26 mA, according to the info in "The Art Of Electronics". Anything below 20 mA, and the audio level will be reduced. I've seen short circuit currents in the 30 to 60 or more mA range, depending on the distance from the CO.
I don't understand how you can say "120 mA draw" (see above) if the current is limited to something less.
-- #======P=G=P==k=e=y==a=v=a=i=l=a=b=l=e==u=p=o=n==r=e=q=u=e=s=t======# | John Lundgren - Elec Tech - Info Tech Svcs. | jlundgre@delta1 | | Rancho Santiago Community College District | .deltanet.com | | 17th St at Bristol \ Santa Ana, CA 92706 | http://rsc.rancho| | My opinions are my own, and not my employer's. | .cc.ca.us | | Most FAQs are available through Thomas Fine's WWW FAQ archive: | |http://www.cis.ohio-state.edu:80/hypertext/faq/usenet/FAQ-List.html| | "You can flame your brains out -- it won't take long." | #===T=u=z=l=a==C=o=m=p=a=n=y=.=.===t=h=r=e=e='=s==L=e==C=r=o=w=d=!==#
John Lundgren <jlund...@delta1.deltanet.com> wrote: >Edward Lawrence (eal) penned: >: I don't know where this started, so I might be redundent with my comments.
>: 1. The phone company puts appx. 50 volts on your line, through the >: equivalent of about 1000 ohms in series. If your phone is 'on hook', a normal >: Voltmeter will read that 50 volts. >: 2. When you take your phone 'off hook', the voltage will drop. How >: much? Depends on the phone. I have seen readings of 7 to 26 VDc. If another >: extention phone goes 'off hook', the voltage will drop a bit lower.
-------------------------------------------------------------- Some outdoor connection boxes have the new loopback tester modules that permit remote operator performed loop-back testing, and free of charge, then the operator can test your line to, but not including, your home wiring. The voltage past these is 25 or 26 volts, so lately the off-hook voltage is much lower, down in the 3 to 7 volt range during dial and busy tones and for talking when connected. -Steve
>: A 28 VDC, 5 K ohm relay wired directlt across the telephone line will >: normally drop out when a phone goes 'off hook', while not loading the line too >: badly. I made a telephone recorder activation circuit this way, and added 200 >: or so turns arould the coil to pick off the audio. Worked first time!
>That's way too much load on the line IHMO. The ampunt of current drawn by >the relay during the on hook is way too high: several milliamps! The CO >may measure this and determine that there is too much leakage current and >try to repair the lines. This could cost you the service call if they >find that the problem is in the CPE (customer provided eauipment). Or >the current could cause the switch to think that the phone was off hook >all the time, and then it would disable the line.
>: Hope this helps.
>| John Lundgren - Elec Tech - Info Tech Svcs. | jlundgre@delta1 |
----------------------------------------------------- If the person, whose net address was deleted, is in the USA or Canada, the co will simply busy out your line and drop voltage to it till it is repaired. Under our current (sic) service agreement it is the user's responsiblity to arrange for private repair of their own lines or report and schedule repairs done by The Phone Company. The computers recheck the line periodically to see if the shorted condition has been changed. Telephone techs regularly short the pair of wires to busy them so they don't get bit by the 90V square wave ring signal anyway without any harm to the system and without telling the co.
They also do this in event of emergencies and excessive calling making an overdemand on the exchange. You simply leave the phone off the hook till your place in the queue comes up, and then you can make your call when the dial tone pops on!
Richard Steven Walz (rste...@armory.com) wrote: : In article <4gq4su$...@news2.deltanet.com>, : John Lundgren <jlund...@delta1.deltanet.com> wrote: : >Edward Lawrence (eal) penned: : >: I don't know where this started, so I might be redundent with my comments. : > : >: 1. The phone company puts appx. 50 volts on your line, through the : >: equivalent of about 1000 ohms in series. If your phone is 'on hook', a normal : >: Voltmeter will read that 50 volts. : >: 2. When you take your phone 'off hook', the voltage will drop. How : >: much? Depends on the phone. I have seen readings of 7 to 26 VDc. If another : >: extention phone goes 'off hook', the voltage will drop a bit lower.
It seem to me like basically, when the phone is on-hook, it is taken out of the loop, and when it is on-hook, it acts like a resistor across the two wires???
So what happens when the phone is supposed to ring (ie. how does the phone know when to ring and what kind of voltage is across the two wires?).
Also, how much current can the phone line provide (thinking of using it to power some transistor for switching etc).
I do have a simple circuit that detects a phone off the hook condition and lights an LED (or opto-isolator). This can then be used to drive other circuitry.
It is self powered (from the line) and complies with the line loading requirements, ie 50uA on the hook, 5mA off the hook.
Hundreds of these have been built. If you want a copy of the circuit, I can mail it to you as text plus 2 off UUEncoded GIF files. The circuit is only three transistors, five diodes and a few resistors.
In article <4gifp6$...@fcnews.fc.hp.com>, Edward Lawrence <eal> wrote:
>I don't know where this started, so I might be redundent with my comments.
> 1. The phone company puts appx. 50 volts on your line, through the >equivalent of about 1000 ohms in series. If your phone is 'on hook', a normal >Voltmeter will read that 50 volts. > 2. When you take your phone 'off hook', the voltage will drop. How >much? Depends on the phone. I have seen readings of 7 to 26 VDc. If another >extention phone goes 'off hook', the voltage will drop a bit lower.
> A 28 VDC, 5 K ohm relay wired directlt across the telephone line will >normally drop out when a phone goes 'off hook', while not loading the line too >badly. I made a telephone recorder activation circuit this way, and added 200 >or so turns arould the coil to pick off the audio. Worked first time!
I don´t know about the US tele systems but with the scandinavian systems, measuring the voltage is not sufficient according to specifications. This is because modern telephone switchers can have as low voltage as 7-15 volt when on-hook and nearly zero volt when on-hook.The only safe way is to measure the current as the specification tells that a absolute minimum of 9ma will always float when off-hook and a maximum of 25ua when on-hook. Of course there is still problem measuring current... The maximum serial resistance added should be 75 ohms. This gives a pretty low voltage fall over the resistor...
Stig Andersson (y...@multi.se) penned: : I don´t know about the US tele systems but with the scandinavian : systems, measuring the voltage is not sufficient according to : specifications. This is because modern telephone switchers can have as : low voltage as 7-15 volt when on-hook and nearly zero volt when : on-hook.The only safe way is to measure the current as the : specification tells that a absolute minimum of 9ma will always float : when off-hook and a maximum of 25ua when on-hook. : Of course there is still problem measuring current... : The maximum serial resistance added should be 75 ohms. : This gives a pretty low voltage fall over the resistor...
: Stig
If most phones only had 9 mA of current, the sound would be too weak to be heard. I think Bell standards require 3 times that much.
If the telephone instrument is powered by the line, then there has to be enough power to get the job done. The subscriber loop can have more than a thousand ohms resistance, so there has to be enough voltage to overcome this and give the needed current. That's why the on-hook voltage is 48 volts in the U.S., and off hook is may drop to under 10 volts.
Whatever method is used to sense the voltage, it should be isolated from the high voltages and currents that can be on the phone line when lightning storms are nearby.
-- #======P=G=P==k=e=y==a=v=a=i=l=a=b=l=e==u=p=o=n==r=e=q=u=e=s=t======# | John Lundgren - Elec Tech - Info Tech Svcs. | jlundgre@delta1 | | Rancho Santiago Community College District | .deltanet.com | | 17th St at Bristol \ Santa Ana, CA 92706 | http://rsc.rancho| | My opinions are my own, and not my employer's. | .cc.ca.us | | Most FAQs are available through Thomas Fine's WWW FAQ archive: | |http://www.cis.ohio-state.edu:80/hypertext/faq/usenet/FAQ-List.html| | "You can flame your brains out -- it won't take long." | #===T=u=z=l=a==C=o=m=p=a=n=y=.=.===t=h=r=e=e='=s==L=e==C=r=o=w=d=!==#
On 21 Feb 1996 08:42:47 -0500, oron...@aol.com (ORONITI) wrote:
Here´s a simple and working solution. Use two optocouplers with the diode side in serial with the line and pointing one in each direction. Connect outputs in paralell and use as "OC".
I have used two PC815 which have sufficiient CTR to work at currents as low as 5ma. If line currents exceeds 50ma you may connect a pair of diodes in series, paralell with the opto-diode, pointing each way.
Stig Andersson (y...@multi.se) penned: : On 21 Feb 1996 08:42:47 -0500, oron...@aol.com (ORONITI) wrote:
: Here´s a simple and working solution. Use two optocouplers with the : diode side in serial with the line and pointing one in each direction. : Connect outputs in paralell and use as "OC".
That's kind of a waste of opto's. Why not use a diode in series to make sure it will not work if connected backwards.
: I have used two PC815 which have sufficiient CTR to work at currents : as low as 5ma. If line currents exceeds 50ma you may connect a pair : of diodes in series, paralell with the opto-diode, pointing each way.
: Stig
CTR = Current Transfer Ratio?? I'm not sure.
MCT-2 opto's seem to be the popular choice for this app in the schems I've seen. I thought about using this circuit for a long time, but I abandoned it because of a couple reasons.
It has to be put in series with the line at the point where the line enters the dwelling if it is going to sense all the phones. So that means that another pair of wires has to be run to all the locations where the off-hook condition is to be used/sensed. That can add up to a lot of wire.
It can be damaged be high fault currents that might be caused by lightning or other high voltages. The LED of the opto should have a low value resistor across it, such as 100 ohms or maybe less. Or if the rectifiers are placed across it, then they should be high current ones. The resistor wil reduce the current from the line at all times, so it has to be selected for the particular line, which may have a large difference in current depending on the distance from the CO. This is another problem.
The voltage sensor that runs off batteries is the best solution. The one I built and works is the one in the group of schematics that uses three volts from two D cells and has two transistors. The header says that it was posted by a guy from Canada whose last name is Boisvert.
Never use any of those circuits that have one side of the phone line connected to the circuit or to ground. That's BAD. The phone line will become unbalanced and it could be hazardous.
-- #======P=G=P==k=e=y==a=v=a=i=l=a=b=l=e==u=p=o=n==r=e=q=u=e=s=t======# | John Lundgren - Elec Tech - Info Tech Svcs. | jlundgre@delta1 | | Rancho Santiago Community College District | .deltanet.com | | 17th St at Bristol \ Santa Ana, CA 92706 | http://rsc.rancho| | My opinions are my own, and not my employer's. | .cc.ca.us | | Most FAQs are available through Thomas Fine's WWW FAQ archive: | |http://www.cis.ohio-state.edu:80/hypertext/faq/usenet/FAQ-List.html| | "You can flame your brains out -- it won't take long." | #===T=u=z=l=a==C=o=m=p=a=n=y=.=.===t=h=r=e=e='=s==L=e==C=r=o=w=d=!==#
On Tuesday, February 13, 1996 3:00:00 AM UTC-5, James W. Lynch wrote:
> Does anyone have plans for a simple off-hook detector? I need to know
> when someone has lifted a receiver. A dial-tone detector circuit would
> also work.
> Any suggestions?
> Thanks,
> Jim.
was there a receiver off hook tone called a queue tone?
In article <v6bt98970ban0ktp8t8e5icffifqq5e...@Osama-is-dead.net>,
G. Morgan <sealte...@osama-is-dead.net> wrote:
> Andrew Smallshaw wrote:
> >On 2012-11-10, robbiedca...@gmail.com <robbiedca...@gmail.com> wrote:
> >> On Tuesday, February 13, 1996 3:00:00 AM UTC-5, James W. Lynch wrote:
> >>> Thanks,
> >>> Jim.
> >> was there a receiver off hook tone called a queue tone?
> >I think it is unlikely Jim is still looking at this 16 years after
> >initially posting.
> Lol... good catch. I almost answered!
Look! It's the amazing Google NecroThread<TM>
This just might be the oldest one I've seen to date. About 3 weeks ago in another group I haunt, one came to life (obviously another google groups inspired incident) after 7 years dead.
-- If the door is baroque don't be Hayden. Come around Bach and jiggle the Handel
On Sat, 10 Nov 2012, Don Bruder wrote:
> In article <v6bt98970ban0ktp8t8e5icffifqq5e...@Osama-is-dead.net>,
> G. Morgan <sealte...@osama-is-dead.net> wrote:
>> Andrew Smallshaw wrote:
>>> On 2012-11-10, robbiedca...@gmail.com <robbiedca...@gmail.com> wrote:
>>>> On Tuesday, February 13, 1996 3:00:00 AM UTC-5, James W. Lynch wrote:
>>>>> Thanks,
>>>>> Jim.
>>>> was there a receiver off hook tone called a queue tone?
>>> I think it is unlikely Jim is still looking at this 16 years after
>>> initially posting.
>> Lol... good catch. I almost answered!
> Look! It's the amazing Google NecroThread<TM>
> This just might be the oldest one I've seen to date. About 3 weeks ago
> in another group I haunt, one came to life (obviously another google
> groups inspired incident) after 7 years dead.
They go back further. The lefendary thread where Linus announces Linux (and the one where Andrew Tannenbaum argues that Minix is better, if that is a separate thread) has been vandalized in the minix newsgroup, and the announcement is 1991.
In that case, google brought the vandalism on itself. At one point years back they put up a timeline of Usenet, pointing to some "key" threads, which included that Linux announcement. The last time they changed the interface, they "forgot" to keep the ability to reply limited to 30 days (which had always been the case previously), so it allowed the vandalism, and people wanted to leave their mark on important threads. I never did check at google to see if they removed the recent replies or not, I know I complained a bunch of times at the time, including about replies to that thread. Soon/eventually, they fixed that "bug".
But then it happened again when they changed the interface recently, and more vandalism of that thread. INdeed, about the only traffic in the minix newsgroup right now is people replying to that thread, they don't even seem aware of what they are doing.
It's easy to notice these replies to old threads. Suddenly someone is replying to a message you've never seen. Sometimes they even quote the date, other times you just know since it's already happening. Yes, I know messages can go astray, but that happens less and less, unlike the old days. I remember when I was reading some Usenet newsgroups via a local BBS starting in late 1994, and it was relativley common for messages to not make it there, or for a reply to appear before the original post.
The only other reason for seeing a post you haven't seen before is if someone is reading another newsgroup and feels the need to add another one to their reply. It seems to happen a lot less than in the old days.
I think I've seen people reply via google to messages older than 1991, but I'm not certain.
I still can't figure out what someone is replying to an old message. They'd have to do searching going quite far back to find the old message, which then can't be accidental.
On Tuesday, February 13, 1996 3:00:00 AM UTC-5, James W. Lynch wrote:
> Does anyone have plans for a simple off-hook detector? I need to know
> when someone has lifted a receiver. A dial-tone detector circuit would
> also work.
> Any suggestions?
> Thanks,
> Jim.
At this former Concord Telephone Exchange that i've been talking aboutthe receiver off hook tone at the Concord Telephone Exchange that was a medium pitch sound that went like a horn. Was it a siren or buzzer?
On 11/10/2012 06:09 AM, robbiedca...@gmail.com wrote:
> On Tuesday, February 13, 1996 3:00:00 AM UTC-5, James W. Lynch wrote:
>> Does anyone have plans for a simple off-hook detector? I need to know
>> when someone has lifted a receiver. A dial-tone detector circuit would
>> also work.
I once built a circuit to connect two phones to one land line. It
consisted of two relays with each relay's coil put in series with a
phone and a capacitor in parallel to the relay: if you take the receiver
off-hook, a direct current will flow which will cause the relay to
switch and disconnect the other phone. The capacitor was there to allow
the alternating current which carries the voice to pass through.
IIRC the relays' voltage was matching the DC voltage (24V?) and the
capacitors were some very large unpolar (i.e. no tantals or electrolytic).
Please don't ask me to dig the circuit up, it's very deeply buried ;-)
On Tuesday, February 13, 1996 3:00:00 AM UTC-5, James W. Lynch wrote:
> Does anyone have plans for a simple off-hook detector? I need to know
> when someone has lifted a receiver. A dial-tone detector circuit would
> also work.
> Any suggestions?
> Thanks,
> Jim.
What was the telephone receiver off hook tone for the Concord Telephone Exchange Inc. Company in Farragit Tn.
On Tuesday, February 13, 1996 3:00:00 AM UTC-5, James W. Lynch wrote:
> Does anyone have plans for a simple off-hook detector? I need to know
> when someone has lifted a receiver. A dial-tone detector circuit would
> also work.
> Any suggestions?
> Thanks,
> Jim.
What kond of of hook tone did the Concord Telephone Exchange Inc. Company have?
On 2012-11-12, robbiedca...@gmail.com <robbiedca...@gmail.com> wrote:
> On Tuesday, February 13, 1996 3:00:00 AM UTC-5, James W. Lynch wrote:
>> Does anyone have plans for a simple off-hook detector? I need to know
>> when someone has lifted a receiver. A dial-tone detector circuit would
>> also work.
>> Any suggestions?
>> Thanks,
>> Jim.
> What kond of of hook tone did the Concord Telephone Exchange Inc. Company have?
In 1996 line voltage droped from 48V to about 12V when the phone is
taken off hook for any reason (eg to make or answer a call) nothing
has changed since then.
