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Questions tagged [telephone]

A telephone, is a telecommunications device that converts sound into electronic signals suitable for transmission via cables

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1answer
46 views

SIM to RJ: emulating SIM card as a RJ connector [closed]

i recently got in a Goodwill store one of the 2500 model phones https://en.wikipedia.org/wiki/Model_500_telephone#Model_2500 and i want to use it. the problem is that i don't have a phone line in my ...
1
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1answer
68 views

Detect phone call termination

I am designing an automated telephone circuit that will work with the PSTN line. I already had a question to detect the incoming ring signal. Now I want to detect whether the opponent person in the ...
5
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4answers
1k views

CAT5 for telephony

I wish to extend my incoming telephone connection using CAT5 as I've heard it could provide better performance than standard single stranded telephone wire over long distances. There are only two ...
0
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4answers
117 views

TDMA in telephone circuit switching - isn't there delay in transmitting a particular user's speech? [closed]

Let's do a simple case on the left with X and A user telephones. So the way an analog signal (user's speech X) is handled, is that it is sampled at 8000 bits / sec. The high-speed C-channel has 128 ...
0
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1answer
39 views

600 ohm modem transformer impedance calculation by formula

From the datasheet of a modem transformer we have: Impedance, Primary: 600 Ω Typ. @ 1 kHz 1 Vrms* Shunt Inductance Lp, Primary: 3.2 H min. @ 1 kHz D.C. resistance @20°C: Primary = 82 Ω ± 15% ...
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4answers
57 views

Which capacity measurement is the correct way to measure?

So I've seen batteries showing their capacity in mAh and I've seen others showing in Wh. Phone batteries are always measured in mAh, while for some reason BatteryInfoViewer on my computer only shows ...
1
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0answers
137 views

Why telephone lines use -48V not +48V? What’s the difference practically in -ve and +ve voltages? [duplicate]

Why telephone lines use -48V not +48V? What’s the difference practically in -ve and +ve voltages? Detailed answer would be appreciated.
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1answer
172 views

Is it legal to use electricity from a phone line?

I saw a video by ElectroBOOM where he wiretapped his home phone. So, apparently, there is around 40v coming through the phone line, with higher peaks when it rings etc. I have a few questions about ...
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2answers
91 views

General questions about the telephone line a.k.a “last mile” [closed]

Before the digital data gets conveyed over the "last mile", it passes a modem, which converts this digital data into audio signals (Which is often called analog) (but the binary system still is there, ...
0
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1answer
46 views

3x AA battery phone charger input voltage drop

I am using a 0.9-5 V to 5 V dc-dc step up converter to charge a phone using 3 AA batteries, but whenever I plug in the phone it starts charging but the input voltage drops from ~4.5 V to less than 2 V ...
2
votes
2answers
108 views

How are severed phone lines, the ones on utility poles, repaired when they are severed

I have been searching for this answer for a long time and I haven't found any info on the way severed lines are repaired. There must be tens of thousands of tiny wires that must reconnected, and in ...
2
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2answers
302 views

Analog (POTS) telephone off-hook detection

With a single POTS telephone line and two or more handsets, when a call comes in, each handset can join in with the call. This can sometimes be an issue when one user doesn't know the line is in use, ...
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3answers
406 views

How does this old telephone ringer work?

I bought an old rotary phone with the hopes of cannibalizing it for a doorbell/intercom thing in my apartment building. It looks absolutely marvelous inside: However, I'm having trouble figuring out ...
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1answer
3k views

Using a usb-c laptop charger to charge a phone [closed]

I don't really know anything about electronics and I'm not sure if it's the right place to ask, but still. Is it OK to charge my phone with my laptop's charger? Here's info on the laptop charger: ...
11
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3answers
3k views

How does the telephone's keypad work?

I disassembled some old telephone and mobile phone. Every keypad is different, and yet, all of them have those "spirals" (see the image below) under the button or something similar. What I don't ...
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1answer
151 views

Fast charging 2.0: 7V×2.5A, 9V×2A or 12V×1.5A?

The FastCharge 2.0 standard has these charging specifications in the exact same charger (a VoltCraft car charger): 5 V up to 2.0 A (10 W max.) 7 V up to 2.5 A (17.5 W max.) 9 V up to 2.0 A (18 W ...
4
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5answers
112 views

How well does telephone delay correlate to geographic distance?

I have a friend who lives on the other side of the world, and every time we speak over the phone, there's roughly a second of delay between one of us saying something and the other hearing it. I've ...
21
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4answers
4k views

Why do push button telephones use dual-tone for signalling?

Here is a related information from wikipedia: For touchtone service, the signal is a dual-tone multi-frequency signaling tone consisting of two simultaneous pure tone sinusoidal frequencies. ...
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1answer
73 views

iPhone not charging when plugged last [closed]

The power extension has two USB slots. I noticed that when a Xiaomi phone is plugged first, and then iPhone next, the iPhone doesn't charge. However, if it's done in reverse, iPhone first, Xiaomi ...
0
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2answers
1k views

Is it dangerous to continue to remove a slightly punctured phone battery?

I have been trying to replace the phone screen on a Galaxy S7, and therefore had to remove the battery in the process. While doing so, I saw a tiny spark and felt a weird smell. I can't see any damage ...
33
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8answers
5k views

Why do devices stop operating properly in extreme cold?

I have noticed that a lot of smart phones say that they won't operate under -4 degrees F (-20 degrees C). Can anyone explain to me what happens when the phones get cold that stops them from operating?
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2answers
216 views

How to split hybrid two-way audio line?

Intro My apartment has a simple door intercom system which uses a hybrid two-wires line to carry both the receiving and transmitting audio signals for each floor unit. The wires are connected to each ...
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2answers
63 views

Can I charge my phone with a very low amp?

I am working on a charging device for a smartphone, it's for a science project, Currently I finished planning all the electronic parts for it and I am getting ready to start building, however I ...
0
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0answers
185 views

Telephone line isolation

I have a small problem. I have a fiber connection at home, and I want to power both the router and the cordless phone attached to it from the same power supply. Now, if I attach either the router or ...
1
vote
1answer
64 views

Can I use a similar AC adapter with different input but the same output?

I have a landline telephone from Japan. The owners manual says only use OUR AC adapter, {Input 100v 50/60Hz 8VA - Output DC 11V 430mA} I want to use this in North America - can I use a AC adapter ...
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1answer
76 views

Connect RF module to phone to find distance between them

I would like to know if it is possible to connect an RF(radio frequency) module to my smartphone and find the distance between them with an accuracy of about +/-2 meters. To find distance I believe I ...
49
votes
10answers
9k views

Amplification before tubes and transistors were invented

Telephones are older than vacuum tubes and of course transistors. How was signal amplification done? I mean the technology, not the details. EDIT Some additional informations that I should ...
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1answer
64 views

A trio of questions about radio/smartphones [closed]

I know that smartphones can receive FM radio using earbud/built-in antennas, but can they receive amateur radio frequencies (144 MHZ?) and if so, how? Is there a way to sending out radio waves and ...
1
vote
1answer
40 views

What is effect of echo canceller on QAM signals?

During data call or fax call echo cancellers are switched off in entire path from phone to exchange and exchange to phone. Echo canceller are used to cancel echo during voice call. Modulation in data ...
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votes
2answers
124 views

Is it any possible to convert analog phone to IP phone using Raspberry PI [closed]

I need IP Phone for VOIP purpose. I have Raspberry PI and analog phone. Is there any possibility for interfacing analog phone with Raspberry PI.
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0answers
94 views

What frequency is used for 2400 bps modem on pstn lines?

If dial-up modem is working in 2400 bps .please correct me in the following it can use 1200 hz and 2400 hz or higher till 3400 hz (at max )frquency depending on modulation technque .am I right ? If ...
0
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5answers
832 views

Why telephone dc voltage drops to about 8 volts? [closed]

I found out that the DC voltage supply is about 48 volts in the central office, and the typical line impedance is about 600 ohms. Also the typical current in off-hook state is about 20mA. So with a ...
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2answers
71 views

Can an audion tube amplify a pulsating direct current or must the current be converted first to an alternating current? [closed]

Can an audion tube use a pulsating direct current as input and magnify the signal from the electrons flowing from the filament without first converting it to AC current? The reason I ask is that : I ...
10
votes
4answers
2k views

When a AM radio wave reaches the antenna does the signal need to be in a closed circuit to be amplified?

This needs some explanation. In the diagrams of radio instructions I always see a single line from the antenna to the input for amplification. Let's use a vacuum tube amplifier as for example. There ...
1
vote
1answer
97 views

Is it possible to have “in-out” communication in a single 56k modem?

I'm trying to implement a call blocker using a Raspberry Pi and a Zoom 3095 USB Mini External Modem using a guide I found on the web. The modem used has a single RJ11 jack. It's not clear from the ...
1
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1answer
519 views

How does this telephone circuit modulate the current?

I've been reading on how old landline telephones work (POTS, as they call it) and found out it's quite a bit more involved than I had expected. This circuit comes from the wikipedia article "...
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2answers
68 views

Charging iphone without USB [closed]

I am looking to charge my iphone using a thermoelectric power generation device. The thermoelectric generator device has positive and negative leads, and I have tried connecting the wires from the USB ...
0
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1answer
92 views

What are these elements and what they do?

I have a telephone circuit (Model No. Panasonic KX-TS500MXB) which has following item between TIP and Ring. Do you have any idea what it might be? At first I thought it might be a back to back zener ...
2
votes
1answer
479 views

Is it possible to connect a 3-wire line without stripping an RJ11 line cord?

I have a 302 telephone that was manufactured in 5/39 (May 1939). The line cord does not have a four-prong connector attached; the wires are simply cut. I am trying to get this connected. I have a ...
0
votes
1answer
195 views

How to make a landline phone ring periodically [closed]

How can I use a capacitor to ring a landline phone over and over again. I assume I need to develop such a circuit like below with a cap placed on one of wires. I think the cap would charge, and when ...
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votes
1answer
422 views

how do i convert 12 vdc to 100 vdc to use in central phone? [closed]

I need a small circuit that convert 12 vdc to 100 vdc to use in central phone that can ring the phone.the current is maximum 150 ma.how can i do it? thanks
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0answers
548 views

Connect speaker directly to Galaxy S5. Minimum impedance accepted

I want to connect an external (passive) speaker (3W/16 ohm) directly to my Samsung Galaxy S6 using the headphone jack. Is the impedance too small? What is the minimum impedance that I can use? Is 16 ...
0
votes
1answer
49 views

DC power filter curicut

I have a problem in powering my wireless Panasonic landline telephone. It works on 9v power with a transformer that work on 220v and gives as output 9v and it works fine with this way. I try to power ...
2
votes
2answers
98 views

How do switches respond when more than 10 dial pulses are sent?

Forgive me if this is off topic but this is actually about circuitry design: My understanding is that electromechanical Strowger SxS switches have 10 "steps". What would happen if 11 pulses were ...
0
votes
1answer
53 views

How can I get a line cord to stay in a broken modular jack? [closed]

I have quite a few telephones. One I bought supposedly broken but I fished the jack out of the phone and found part of the connector was missing. A line cord could still snap in. Today, I was ...
0
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2answers
102 views

Multi-channel Wireless Microphone vs Home Wireless Telephone System

I'm curious why a wireless microphone system for school plays requires a multi-channel receiver while a home telephone system allows as many conversation participants as there are handsets with only ...
2
votes
1answer
78 views

Using BJT emitter follower after microcontroller

I am trying to understand an already existing circuit shown below taken from http://boris0.blogspot.fr/2013/09/rotary-dial-for-digital-age.html. The aim of this circuit for the right part is to ...
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0answers
162 views

Is it technologically possible for IVR systems to recognize and support pulse dialing

I understand all the concepts behind IVR systems. I've never been able to quite understand why pulse dialing can't be used with IVR systems. Tones are obviously sent to the other party, but a pulse ...
1
vote
1answer
543 views

Phone charging current draw [duplicate]

I want to use a power regulator PCB I designed to switch down 60V to 12V and 12V to 5V in order to power a USB plug and use it as a phone charger. My only worry is that the switching regulators I am ...
0
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3answers
157 views

How to a build a payphone controlled iPhone? [closed]

I'm trying to create a project for my kitchen that involves using the shell of an old payphone and a modern cell phone ( perhaps iPhone ) to actually make calls. Basically, I would like the user to be ...