# Phone Line Light?



## Radiant (Jun 11, 2004)

Anyone ever thought about making a nightlight out of a phone jack splitter by putting an LED in it? How much power can you draw from a phone line anyways? It would be good for power outages since the phone line is seperate.


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## PhotonWrangler (Jun 11, 2004)

[ QUOTE ]
*Radiant said:*
Anyone ever thought about making a nightlight out of a phone jack splitter by putting an LED in it? How much power can you draw from a phone line anyways? It would be good for power outages since the phone line is seperate. 

[/ QUOTE ]

If you draw more that around 18 milliamps, the central office will think your phone is "off-hook" and you won't be able to make or receive calls on that line while the LED is lit.

However using one of those LED boost regulator chips might work. It might be able to come up with enough drive to light the led(s) without loading down the line. *Until* the phone rings, that is.....

An on-hook phone line is nominally 48vdc. But a *ringing* phone line presents 100vac!!! That would tend to blow out a directly-connected LED or boost regulator circuit.
/ubbthreads/images/graemlins/eek.gif


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## Doug Owen (Jun 11, 2004)

PhotonWrangler has once again hit the nail square on the head. Well when he said 'LED boost regulator chips' he really meant 'down (or buck) converter', but the rest was spot on. 

And for sure that 90 volt 20 cycle square wave will get you back into church when ma bell tries to ring the bell.

OTOH, some phone jacks have 8 volts AC or so on the yellow (normally ground) and black leads. It comes from the local mains to light bulbs. This could easliy be made to serve.

Doug Owen


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## Darell (Jun 11, 2004)

[ QUOTE ]
*Doug Owen said:*
And for sure that 90 volt 20 cycle square wave will get you back into church when ma bell tries to ring the bell.


[/ QUOTE ]So the bottom line here is that those of us who expect phone calls are screwed if we've dangled an LED (with or without driver) off the line? I've toyed with this idea for years. And as usual, a little knowledge can be dangerous!


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## BatteryCharger (Jun 11, 2004)

Hmmm...I don't have a land line, only a cell phone. Might I still be able to barrow some electricity from my phone jacks? /ubbthreads/images/graemlins/smile.gif 

I was installing a phone jack once and was stripping the wire with my teeth. The phone wrang. SURPRISE! /ubbthreads/images/graemlins/icon15.gif


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## 14C (Jun 11, 2004)

The standard line has a 48VDC source (battery) but that voltage is dropped by line resistance and the voltage seen at the termination (jack) is usually lower....depends on distance from the CO.

As mentioned above the ringing generator sends (usually in the US) 90-110 VAC over the line.

The CO detects an "off hook" condition based on current, also metioned above.

One more thing the DS0 cards can only supply a limited anmount of current. This is why all phonesets used to be rated with a "ringer equivalence" number. Too many phones connected to the line could damage a DSO circuit card. They seem to be better protected today but I think there is still a limit to the current that can be drawn and the time it is drawn before damage occurs.

The local Telco will NOT be happy with you if you muss a hair on their head and could terminate service.

All that said, there is NO reason not to hand an LED off of the line if you buffer and drive it properly...but it would probably be expensive to build a circuit that would protect your LED AND the Telco off-premesis equipment.


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## gadget_lover (Jun 12, 2004)

It's not hard to do. I was a telco guy for many years. I still have a LED test light in my tool kit. I used it to check if the line was live (battery and ground). I had it set up with a 48v lamp so that I could draw dial tone.

As was said, the 48V drops unless you have a repeater on your line. If the resistance drops low enough to draw an appreciable current it will try to give dial tone, then will eventually give up and turn off your circuit.

As I recall the ringing current was actually pulsating DC. That allowed us to have 2 party lines, where a phone #1 and phone #2 had diodes in line with their bells. Only one or the other would ring, depending on the polarity applied to ringing current. It also kept us from getting fried when a call was placed to a line we were working on. I'd get stung several times each day when working in the central office.

A low current night light powered by the phone company can be accomplished. Don't be suprised if you find your phones answering and hanging up on the first ring (called ring-pre-trip). Don't be suprised if the call you make to hong-kong doesn't disconnect as soon as you hang up. It all depends on how close you get to the borderline.

Daniel


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## BatteryCharger (Jun 12, 2004)

Now that I think about it, I used to have a tester from radio shack. You plugged it into the phone line, and a green LED lit up if all was good, and a red LED lit up if something was backwards. I don't know how it worked, but there couldn't have been much more than a resistor.


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## 14C (Jun 12, 2004)

gadget_lover and BatteryCharger, the ringing generators I used were litlle (3.5x6x5 or so) steel-cased units that could be run ny the 48 VDC power supplies. I think you are right about pulsing in the sense that they put out a square wave. I too had the testers. and in fact may still have one somwhere.

The plug into the RJ-11 and some have polarity indicating LEDS.

I never saw one deal with ring voltage though so I could not say if they would survive it.

BTW it took me a few minutes the other day but when a co-worker asked I finally remembered that the handset jack is an RJ-8...how's that for stupid detail?


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## andrewwynn (Jun 12, 2004)

I was researching some telco-interfaced doorbells and stumbled into this page once:

sandman's telco-powered products 

Check 'em out... you can apparently run a fair amount from telco.

I have one of those testers that checks for polarity... i actually found a phone once that cared.. the new ones don't really. I took an old ®S model apart once and only remember an LED and resistor... they make a double-LED... one each way.. red one polarity green the other... and if you apply ac you get a mix that looks orange.... so it must use one of those.

I never had a ring come in when using the tester... but it might pull enough current to drop the dial tone, i can't remember testing that...

I simple zener diode and resistor should short the ring to ground .... i measured 20Hz 80VAC after i got ZAPPED once not realizing... the low current DC never felt it even though it usually measures between 48 and 52VDC.... now ya got me curious... think i'll have to do some playing /ubbthreads/images/graemlins/wink.gif


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## PhotonWrangler (Jun 12, 2004)

[ QUOTE ]
*Doug Owen said:*
And for sure that 90 volt 20 cycle square wave will get you back into church when ma bell tries to ring the bell.

[/ QUOTE ]

You sound like a telephony professional, Doug. /ubbthreads/images/graemlins/smile.gif
Yes, 90vac at 20 hertz exactly.

Been "surprised" by that ringing voltage many, many times! 
/ubbthreads/images/graemlins/rolleyes.gif

[ QUOTE ]

OTOH, some phone jacks have 8 volts AC or so on the yellow (normally ground) and black leads. It comes from the local mains to light bulbs. This could easily be made to serve.

Doug Owen 

[/ QUOTE ]

Good point, Doug. In the installations I've seen, that low voltage AC usually originates from a wall-wart transformer located somewhere inside the house. That was used at one time to light an incandescent lamp underneath the dial in the old "Princess" phones.


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## PhotonWrangler (Jun 12, 2004)

The tone generators that I use do indeed have a dual-color LED (back-to-back chips) and a current-limiting resistor inside. There is also a zener regulator to keep the incoming ring voltage from turning the LED into an NED.
/ubbthreads/images/graemlins/wink.gif

Sometimes my toner will cause the phone line to go off-hook and block incoming calls; sometimes it doesn't. As 14c mentioned, it depends on the sensitivity of the telco's DSO (voice) interface, as well as how much loop current is flowing on that line, which is affected by the distance from the central office, the integrity of the physical splices and punchdowns, and other stuff.

I've never measured the ringing voltage on a VOM or a 'scope to verify whether it's AC or pulsed DC, but my tester will show a dual-color flash during the presence of ringing voltage, which indicates to me that it's AC. Or pulsed DC in the opposite polarity of the -48vdc battery, which is still effectively AC.

Sandman is a cool resource for oddball and inexpensive telephone tools and gizmos. Their catalog is almost a crash course in telephony in itself.


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## James S (Jun 12, 2004)

An elderly lady phoned her telephone company to report that her telephone failed to ring when her friends called -- and that on the few occasions when it did ring, her pet dog always moaned right before the phone rang. The telephone repairman proceeded to the scene, curious to see this psychic dog .... or the senile elderly lady. 

He climbed a nearby telephone pole, hooked in his test set, and dialed the subscriber's house. The phone didn't ring right away, but then the dog moaned loudly and the telephone began to ring. Climbing down from the pole, the telephone repairman found: 

1. The dog was tied to the telephone system's ground wire via a steel chain and collar. 

2. The wire connection to the ground rod was loose. 

3. The dog was receiving 90 volts of signaling current when the phone number was called. 

4. After a couple of such jolts, the dog would start moaning and then urinate on himself and the ground. 

5. The wet ground would complete the circuit, thus causing the phone to ring. 

Which goes to show that some problems can be fixed by pissing and moaning.

--------

Thats almost certainly an "apocryphal" story /ubbthreads/images/graemlins/wink.gif but it's what I thought of when I was reading this thread /ubbthreads/images/graemlins/grin.gif


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## PhotonWrangler (Jun 12, 2004)

[ QUOTE ]
*James S said:*
...Which goes to show that some problems can be fixed by pissing and moaning.


[/ QUOTE ]

LOL!! /ubbthreads/images/graemlins/crackup.gif Thanks for the laugh, James. I'm gonna pass this along to my friends in the phone biz.


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## Doug Owen (Jun 12, 2004)

[ QUOTE ]
*Darell said:*
[ QUOTE ]
*Doug Owen said:*
And for sure that 90 volt 20 cycle square wave will get you back into church when ma bell tries to ring the bell.


[/ QUOTE ]So the bottom line here is that those of us who expect phone calls are screwed if we've dangled an LED (with or without driver) off the line? I've toyed with this idea for years. And as usual, a little knowledge can be dangerous! 

[/ QUOTE ]

Not necessarily. Several options exist, not all that practical. For instance, a bridge rectifier in front protects from reverse voltage. An inductor in line would protect from the AC from the ring generator. Still, the current available before tripping dial tone is pretty small.

And you can always build your driver to tollerate the high voltage hits.

Years ago I worked for a DC fluorescent light company (mostly 12 volt), but we made 24 (for city use) and 48 volt versions for ma bell. We tried, but failed to make one that would run on 48 from the 'ring and tip' (the two working wires) on rural pay phones at their request. I forget the number for the available current, but we couldn't run the smallest light we could build (probably under a Watt). That is we couldn't have a few dozen mA if the phone company was co-operating (using a 'high current L1 relay' at the CO), something we cannot count on at home.

There might be an option of taking a small current and charging a local battery for use when you need the phone of course (something not allowed on the pay phone project, they wanted the booth itself modestly lighted at all times).

Doug Owen


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## gadget_lover (Jun 12, 2004)

[ QUOTE ]
*James S said:*
An elderly lady phoned her telephone company to report that her telephone failed to ring when her friends called -- and that on the few occasions when it did ring, her pet dog always moaned right before the phone rang. The telephone repairman proceeded to the scene, curious to see this psychic dog .... or the senile elderly lady. 

He climbed a nearby telephone pole, hooked in his test set, and dialed the subscriber's house. The phone didn't ring right away, but then the dog moaned loudly and the telephone began to ring. Climbing down from the pole, the telephone repairman found: 

1. The dog was tied to the telephone system's ground wire via a steel chain and collar. 

2. The wire connection to the ground rod was loose. 

3. The dog was receiving 90 volts of signaling current when the phone number was called. 

4. After a couple of such jolts, the dog would start moaning and then urinate on himself and the ground. 

5. The wet ground would complete the circuit, thus causing the phone to ring. 

Which goes to show that some problems can be fixed by pissing and moaning.

--------

Thats almost certainly an "apocryphal" story /ubbthreads/images/graemlins/wink.gif but it's what I thought of when I was reading this thread /ubbthreads/images/graemlins/grin.gif 

[/ QUOTE ]


We had a similar situation.

The phone would ring once and stop. It only happened on cold, wet (fog or dew) mornings. The repairmen diagnosed is as everything from a bad phone to bad line between the pole and the house and on and on and on.

I finally talked them into testing it on a wet morning by disconnecting the wires at the pole. It still happened. A "troubleshooter"(r) was called in. He found a dead slug in the terminal box a mile from the house. 

When it was wet, the slug would conduct just enough to trip the line when ringing current was applied. When the sun dried it out it went back to it's
high resistance state.

To bring this back on topic, many slugs do floresce under UV light /ubbthreads/images/graemlins/smile.gif


Daniel


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## PhotonWrangler (Jun 12, 2004)

Hmm, so that would'a been a hardware bug. /ubbthreads/images/graemlins/ohgeez.gif /ubbthreads/images/graemlins/rolleyes.gif


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## idleprocess (Jun 12, 2004)

[ QUOTE ]
*andrewwynn said:*
I was researching some telco-interfaced doorbells and stumbled into this page once:

sandman's telco-powered products 

Check 'em out... you can apparently run a fair amount from telco.

[/ QUOTE ]

Smells.... funny to me.

Assuming that ring voltage won't screw up any of these miraculous appliances, 10mA x 48V DC = 480mW - not much in the way of power.

There are other problems with that page... Chernobyl nuclear scientist? Huh? Check out the toothbrush - notice how eerily similar it is to, oh, the Crest Spinbrush model of a year ago? The "vibrator" is a hoot - it's no coincidence that it's "glow in the dark" since it looks eerily similar to something sold in "novelty" shops. 

Then there's the TDMA cellphone - cellphones routinely dissipate more than a watt when operating. Who in their right mind would modify a cellphone to run off telco power when you could cover the entire market with a few models of battery chargers?


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## andrewwynn (Jun 13, 2004)

The telco-powered stuff for the most part certainly relies on the low-draw and store in a battery for high draw during use..

Those anecdotes are hilarious thanks for the laughs.


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## gadget_lover (Jun 13, 2004)

[ QUOTE ]
*idleprocess said:*


Smells.... funny to me.

Assuming that ring voltage won't screw up any of these miraculous appliances, 10mA x 48V DC = 480mW - not much in the way of power.


[/ QUOTE ]


480mw is a usable amount. A 1 watt luxeon underdriven to 480mw will produce a usable beam. I can see an emergency lighting system... Well not really, but it is a cute idea.

Daniel


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## PhotonWrangler (Jun 13, 2004)

How about a high efficiency solar panel and a storage battery instead? It can provide more power, you don't have to mess with that 100vac ring-voltage problem, and it won't annoy the phone company.
/ubbthreads/images/graemlins/wink.gif


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## gadget_lover (Jun 13, 2004)

Yup. got one of those in my tool shed (solar panel and a storage battery). It's good combination.

Daniel


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## PhotonWrangler (Jun 13, 2004)

[ QUOTE ]
*gadget_lover said:*
Yup. got one of those in my tool shed (solar panel and a storage battery). It's good combination.

Daniel 

[/ QUOTE ]

Do you use it to illuminate your tool shed? What kind of lamp does it use?


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## gadget_lover (Jun 13, 2004)

Yes, I use it to light the shed. I use a small solar cell to charge a left-over batttery from a UPS (12 v, 7 ah). The battery is wired to a pair of automobile dome lights from Kragens. They are the kind with a switch. 

I put a white LED in the lens of the light nearest the door. It has a simple resistor to limit the current to a few milliamps. I just want to locate the switch with the LED, not light up the shed. The lamps themselves are a couple watts. I should replace them with Luxeons, but haven't gotten that far.

Daniel


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