I want to put an LED to test my phone line, which I found to be ca 50v.
Where/how do I find the right LED?
THe LEDs at Radio Shack are all like 2v (yea I remember VCC of 2.3 on diodes in my EE2 for non EEs course).
Should I just use a regular bulb, like the kind used for Christmas lights, instead? (what about the LEDs used for CHristmas lights? Shouldn't they work?)
Are yo trying to use the phone line to light an LED and save electricity???? The led will make it look like you want to make a phone call and will get the phone company disconnecting your line in short order. If you only want the led to glow dimly, then use a series resistor to limit the current to 1-2 milliamperes. That may not be enough to trigger the phone company circuits into believing you want phone service.
Reminds me that back in the day, the radio studio phone had two lights that flashed instead of a ringer. The lights looked like a salt and pepper set. Maybe the OP could put a neon lamp across the phone line.
It depends on what he wants the leds to do, light up the room, or only light up when the phone is ringing. 50 years ago I designed the telco circuits that detected when a customers wanted service. It was a pain to distinguish between a real off-hook from the customer and line leakage due to poor cable insulation, squirrels, etc.
If he wants it to light up the room, he'll have to protect it when ringing voltage is present on the line.
I had an old Automatic Electric phone containing a pot marked off in terms of distance from the CO. I guess there were some long loops in the rural areas served by the independent telcos who were Automatic Electric's main customers.
Here's a picture of one of the "saltshaker" ringer lamps. Although this one is stuck to the dial of a dialless phone:
Telco keeps screwing up my phone line (ca every 18mo for the pst 10yrs) and insists they need to come in because it's my fault. Usually they cut my line while they are installing a neighbor's line. Most recently, it prolly was the squirrels. So, instead of removing ten gadgets to prove it's their fault, I want a one second op
I found the earliest undivided phone line netering my house and put a 2way
2pole switch on it so I can switch from the main ingoing line to an RJ11 jack.. but I said, why should i need to hook up a phone to this to test the line, why not an LED.. Ok, it seems I need 2.7K resistor in series.. seems easy'nuff.. since it switches on only momentarily, I wonder if I'm overkilling
And as soon as you tell them you did that they will have justification to blame YOU for the whole damn thing, or whatever it is that you're complaining about. You might even find a charge for a service call on your bill as well.
If you understand anything about telephone equipment, your line sits at 48VDC when the phone in on hook, (hung up). When it rings, an AC voltage, usually at a frequency of 20HZ is superimposed on the line. When you, your fax machine, or modem etc. "answers" the call your line goes "off hook". During this condition a line "loop" current, usually in the order of around 20ma. between your house and the central office), commonly referred to as the CO is developed. The central office equipment detects this current and removes the ringing voltage, and a conversation is established between you and the caller. At this point your line is sitting at about 6VDC until you hang up, whereupon the line returns to 48VDC.
An LED, (along with the appropriate series resistor) will only draw a few milliamps from a 48V line so I don't think that it would trigger an off hook detection, however I really don't understand what it is you are actually trying to accomplish.
If you need an indication of the 48V look at it with a meter or just pick up the phone and listen for dial tone. If it's a visual indication of ringing current you need I'm sure that you can find a schematic on line to build one, or as previously mentioned you can just use an NE2 neon bulb with a small resistor in series. This will draw no current until the phone rings. There are also several commercially made units available that will do this. I would start with Radio Shack. They used to have these. I don't know if they still do. Keep in mind though that if anything you hang on a phone line in any way interferes with it, and it is determined that the device was not FCC registered, ( or probably even if it was) the phone company can come at you full bore. Lenny
good explanation. I just reread what I posted, arrrrggg!
To find the EXACT ranges involved look for the FCC Part 68 telco requirement [antique] that later became the IEEE??? spec
That document will tell you the EXACT ranges to expect [required] from your telco company.
from memory holding current for the OFF HOOK state can be as high as
100mA *and* the resistor required to get that OFF HOOK status can get really warm - if you use a resistor If you use a transistor, you need to use a metal can type [again, for the potential heat] something like
2N2222A, or such.You can actually kill a 2N3904, plastic.
Your problem can be the house wiring. Once I had excessive noise on the line that sounded like a stick rubbing the side of the house. I compained and they said it was inside our building! also didn't charge me anything to tell me that. I started removing 'legs' of the telco wiring, until I found a section that if removed all noise went away!. Seems the red/black wiring spool from Radio Shack had turned 'leaky' Didn't need that section so left it out. Then the next year same type of problem, but this time they said it was a failed pair inside one of those huge cable bundles they string through the city underground. They switched pairs and all was fixed.
Lesson? pretty much HAVE to be able to CUT the wiring at your house as though you're never connected to find what's wrong, else there is endless finger pointing.
You can do a lot with a simple voltmeter/ohmeter and switch out your phone system. to make measurements. You can use a 9V battery to drive your lines and check for how much current is flowing, should be less than 10uA [again from memory] and typically less than 1uA, else you have problems. You can check the 'balance' on your lines by disconnecting from the telco and use the capacitance measurement to check each line to GND - pipe or gnd in an outlet. That capacitance should be pretty close too, else you'll have problems. That LED won't tell you much might as well use a cheapy phone to check your line with the rest of the house disconnected. Or, just carry a phone out to your connection point.
Ok, I set up a 2p2t switch that turns off my in-home lines and instead goes to an RJ11 jack. The telco says I should test this to see if the problem is mine or theirs. SO far this is SOP.
So then me thinks, why should I have to scramble for a tel set to make a test? Why not just put an LED there? So I need a 2700 ohn resistor in series with the LED. I can still plug in the tel set, but the LED will tell me immediately what is going on as soon as I swich from whole-house to test-circuit.
It depends on what your problem is, you haven''t said if it is a noisy line, no service at all, or WHAT IS YOUR PROBLEM you're trying to fix. If you told us, you might get a good answerrr!!!!!
You would still need to watch out for the AC ringtone, as this will try to stick a huge reverse voltage across your LED on every half cycle. Your resistor can be much higher than 2.7k with modern high efficiency LEDs. I think I would go for around 10k as the series resistor, and also put a
1N4007 diode in inverse parallel with the LED. Of course, this only all works at all, if your telephone operator doesn't use line polarity reversal for line status signalling. It's been a lot of years since I learnt all this stuff at college, but I seem to recall that this used to be the case - at least here in the UK anyway - and was the reason that there was a bridge rectifier in the telephone, so that the polarity inside remained the same, irrespective of what was going on polarity-wise on the line. Perhaps Robert would be more current on that.
Here in the US the telco sometimes would also do line reversal AFTER you acquired the connection! Translates to Touch Tone Dialer didn't work anymore! I haven't heard of it happening lately, but moot point, every phone I've seen simply bridge rectifies and is done with it.
My 1970s WECo phone will not generate dialing tones if tip and ring are reversed -- no rectifier there.
When I worked for the telephone circuit company, two-party lines had tuned ringers: 20 Hz for one party and 30Hz for the other. Is that what line reversal was used for in the UK? to distinguish between parties? Here you had to go to single party service if you wanted touch tone dialing.
I honestly can't remember why it was done. I never worked directly in phone service provision, but back 40 years ago, college courses were 'well rounded' affairs, and as well as the radio TV and electronics course that was my primary module, we also had classes in math and telecom principles. As an apprentice, I did a full 12 hour day at college, one day per week, for five years ...
However, as Robert says, I seem to recall that the line reversal took place after connection acquisition, and was for some kind of signalling purpose. Maybe, it was used by other equipment in the chain to determine that the line had been looped ?
I don't recall ever being taught anything about how party line routing worked here, but it does seem as though that might be a valid way of using line reversal signalling. There is an ex British Telecom engineer lives a couple of doors up from me. He was an exchange engineer as far as I recall, so I guess he should know the system backwards. Next time I see him out in his garden, I'll ask.
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