An MPPT circuit would be an excellent idea but it would have to be done REALLY well. You're probably not going to make a great efficiency buck converter at 10 mucriamps input and 5 meg-ohms though.
I would say that what you care about is grabbing the higher powers available when OFF hook and when it rings.
A real POTS line will not be 0 mA... If that were the case, the line would not be able to be held up or a bias a carbon microphone in the handset.
Rick I think you said you do NOT have a POTS landline ? How are you going to test this devce ? What is the market ?
In Australia there used to be a model of phone, provided by the monopoly phone company, that did something pretty much like that. In the time of dial-up modems when households had to take turns and share the same line for internet and voice calls, such phones were a source of periodic mystery disconnections. Once identified, they were thoroughly despised.
is that the maximum power drawn from the phone line when off hook requires an MPPT circuit. But that's not terribly important. I did some simulation s using a circuit that emulated a fixed resistor of about 7 kohms. It woul d charge up 1 mF to 5 volts in about two ring times.
operating voltage. So clearly that was a bad design.
a phone line via a VOIP box which plugs into your home? That may be. But they can't give you that if you aren't on a fiber. Where my one house is t hey would need to run fiber for some 12 miles or more and they ain't gonna do that. My other house could never use a 56 kbps modem because it's on a pair gain amplifier. Know what that is? When you figure it out you may un derstand that the phone company doesn't update old equipment if they don't have to.
they don't call it an amplifier. That was the term the phone guy used at t he time. Seems it was installed in the 70s when people were getting second lines and they didn't have the copper for it. I was told it was a digital mux using three phone lines to provide some dozen or so connections. I wo uld guess that's one pair each for data in each direction and one for clock ing and sync or just clocking and the sync was in the data.
is what we have until something drastic happens like hover boards (not the ebay kind, the Back to the Future kind).
You aren't thinking this through. The MPPT would be for the off hook and/o r ringing circuit to account for the line resistance. Actually, I'm not ce rtain either one is needed. The ultimate current is limited by spec, so th e MPPT would have limits on the operating envelope.
I think I've said very clearly that all three modes can be useful. Ringing is the highest power mode, but also the most brief. Off hook is second hi ghest power, but still limited in duration in normal operation. On hook is the light weight, but virtually unlimited time with limited average load.
Two modes would have benefit of an MPPT design but I'm not sure just how mu ch benefit. The third mode is highly current limited so MPPT is not useful , just draw the max current you can get away with, ~10 uA. Considering tha t the voltage is 48, this can be a useful buck design, but since it is simp ly on all the time, it might be better to just charge a cap to high voltage and put the buck on the other side operating only when needed and shut dow n the rest of the time.
Not sure what your point is. Who said anything about 0 mA? The carbon mic is only connected when off hook at a voltage of some 3 to 12 volts.
Who said anything about a market? If I were planning to produce the device it wouldn't be a stretch to get a POTS simulator since it is illegal to co nnect it to the phone line until approved. There are adapters that allow c onnection of an unapproved device... at least there used to be. I think th ese days that company may be out of business.
This is a thought experiment.
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Yeah, it was more wishful thinking, I guess. I spent a summer working in the racks at a major exchange, and I still think of rotary switches! Nice dream, tho..
Perhaps, it worked for 99% of the people. Everything is a compromise.
Verizonatal has been deploying fiber to the home (FTTH) for about a decade. It's a GPON network with passive splitters in the outside plant. Your house gets an ONT with passive splitters in the outside plant. The ONT has dedicated phone bandwidth.
Pair gain schemes came in several forms. Some earlier ones were analog FDM, with the second call being hetrodyned up to
3KHz~6KHz; they were awful. In parts of the US, they deployed ISDN-based systems with 2B+D invisible to the user, but that was it under the cover.
I'm not familiar with one using that scheme, but that does not mean they were not used.
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A host is a host from coast to coast.................wb8foz@nrk.com
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No need for compromise. On hook is very close to 48 volts. Off hook is 15 volts or lower. Using 10 volts as a threshold is an engineering error, no t a compromise.
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That means nothing if you already have a copper pair and are in a location where it is awkward for them to install fiber.
Was there something in particular in the links you provided??? You provide links and don't mention anything about them.
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This system is hardly invisible. No 56kbaud modem (not that it matters now , but it did back then, I was lucky to get 14k connections), no DSL. I ask ed if they could swap my line with a true copper pair since they were still available. Since that wasn't required by the tarrif, they wouldn't consid er doing it.
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Still looking for my hover board. When I am here I get Internet through a WISP at maybe 7 Mbps. That's fine, but with everyone staying at home now t here can be congestion in the local network. Over the holiday it was prett y much dysfunctional. Today not so bad. Later this evening it will be slo w. People with hard connections are lucky.
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he systems that carry IP are rather much more prone to interruption by the very sorts of events that require emergency communications. The land line based phone system in comparison is a rock.
ns
I'm in an area where everything is vulnerable. AC, Cell, Internet. The only thing that might still work is a land line. If I really need it, I kn ow where the box is at the end of the lane and can clip onto it. I don't t hink they support pulse dialing anymore, so I couldn't dial by touching the leads with a jumper.
That event has happened exactly zero times in my years. However, I have ha d loss of electricity for days after a hurricane. The roads weren't blocke d, but the power lines were so down it took them over a week to get power r estored. Other times the power has been out for a day. But even if the po wer is only out for an hour or two it is important for the phones to work. Cells only work some percentage of the time here even on a good day. Many areas they work not at all. Verizon doesn't even have coverage in West Vi rginia. If you have a Verizon phone in WV you are always roaming. A cous in couldn't set up her husband's phone because of that. They had to wait u ntil they were in Maryland next.
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There are also various specs for China Export devices :-)
Take a look a "ground bounce" issues caused by finite grounding resistance.
Grounding everything to a single point using equipotential bonding reduces the risks of having different ground bounces in different networks. It doesn't remove the ground bounce, but everything bounces in unison, reducing damage risks.
An example of an equipotential bonding is a short common grounding bar into which all overvoltage protectors for mains, telephone, internet, cable TV etc. entering a house are connected, in addition to any antenna mast ground and the local grounding electrode.
Until they pry it from your cold, dead hands? I have no use for a landline . I don't spend all my time in one place... or I didn't until recently. T his damn virus has me in lock down in central Virginia and the one good thi ng about it is that it's hard to tell the difference from any other time an d now.
But Verizon got their land line back from me 20 years ago when mice got int o the central office and they insisted on coming to the house first. At th e time I was only coming once a month or so. So I'd show up on Saturday an d the phone would be dead. Schedule an appointment at least a week away. The local guy would say it was in the central office. A few days later the y'd call and say it was fixed. A month later I'd check and it was still do wn. Later, rinse, repeat. So after two iterations I called and asked tha t they stop billing me for the charges when the phone is not working. They said they couldn't do that. At the end of three months the phone didn't w ork, but now it was because I was cut off for not paying my bill during the time I didn't have service. Not only would they not fix up the bill, phon e service is paid in advance so they owed *me* for that first month. On to p they wanted $50 to reconnect. It has remained disconnected ever since.
The phone company has always been a big dick. I remember a comedy movie fr om the early 60's about TPC (the phone company) like they were the evil org anization in a spy story. "The President's Analyst" with James Coburn and Godfrey Cambridge. The phone company was portrayed rather accurately I tho ught.
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Yeah phone spammers are extremely sophisticated, they use trojan horses/zero-day exploits to hijack PBX servers and re-purpose them into the equivalent of POTS email-spam servers; and can route calls with spoofed caller ID to telco VOIP exit points anywhere in the world pretty much
Start educating yourself e.g. by doing a Google search e.g. with the following search terms (with quotes)
"lightning" "ground bounce"
When there are multiple networks each grounded by a different grounding electrode, those ground connections have different grounding resistance (and inductance) and different currents (and transients) flowing from/into the ground electrode, the different network reference potentials are going to be different.
In mild cases, ordinary galvanic isolation, such as optoisolators and signal transformers (audio, ethernet etc.) are enough, but these usually withstands only a kilovolt or two.
In severe cases, a much better isolation may be needed, such as fiber connections or using just a single network (e.g. Power over Ethernet avoiding local power supplies).
Niw there;s a good thought experiment and more likely a much more useful thought experiment. How to harness lightning and atmospheric energy. Like maybe baloons with wires in a thunderstorm. NASA like.
Ah yes. my modem had a 12V AC supply and I modified my modem to put
32VDC (via a voltage doubling rectifier) onto the pass-through jack when the modem was off-hook so that I could keep the phones speed dial memory alive, and avoid random disconnections.
Use the playback button to take the phone off hook then if you must play games with scavenging power for free off the utility company. That way you have about 20mA at 48v to play with for powering your answerphone.
You should be able to put the CPU into hibernate mode to wake on keypress sleep currents these days are around 0.1uA.
not explaining how any of this is relevant to the discussion at hand.
You continue to not understand the context. None of this is relevant to th e discussion. Please either explain why you think this is relevant or stop discussing it. Your condescension does not help either.
That is factually incorrect. Optos are commonly found that work up to 5 kV . Transformers are the traditional way of coupling audio from the telephon e network, but are bulky and heavy. As I've already said, capacitive isola tion is more commonly used to couple audio either as a chopped analog or as digital.
You continue to not explain why fiber would be needed to couple a telephone to the telephone network. Are you suggesting we've been doing it wrong fo r the last century?
I think you have taken a left turn from this conversation and are having yo ur own discussion that the rest of us are not a part of.
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