Questions tagged [telephone]

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

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19 views

Advice on mounting 4 wire video door phone with electromagnetic lock [closed]

I need some advice for mounting a video door phone with electromagnetic lock, using 4 wires only and a single power supply. The actual model is HIKVISION DS-KIS202 This is a diagram of what I want ...
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25 views

Vintage Phone, rings on 12volt battery. How can I link this now to ring on an incoming call [closed]

I have purchased a Western Electric vintage phone which works with the modern telephone network and there is a cable out the back that once connected to a 12 volt battery rings out. However, I am ...
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1answer
133 views

Electric shock in water [closed]

In my country, someone died recently due to an electric shock when their smartphone fell in a bathtub. I'm trying to understand what's going on the charger side when a poor quality cable used to ...
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2answers
81 views

Slow usb charger for my smart phone? [closed]

I read that the optimal charger for smartphone batteries is 3.92v (to reduce degradation). Is it possible to implement a system that allows an external "charger" to cause charging to stop at this ...
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1answer
55 views

Number of voice channels for PSTN call

Does Public Switched Telephone Network (PSTN) use two voice channels for a single voice call - one for each direction?
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2answers
82 views

Is there any relation between LJU (Line Jack Unit) and broadband speed? [closed]

My question is about LJU (Line Jack Unit) aka Rosette. I am having BSNL (service provider company) copper line broadband in India. In spite of having wired broadband, I get speeds of 6Mbps(download)...
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1answer
63 views

Getting two way audio from/to a landline telephone, and making it ring

I have a "land line" telephone (ie. with an RJ11 plug) and a CSR8615 HFP bluetooth module (datasheet) — I'm looking to make my mobile's phone calls ring the land line phone, as well as being able to ...
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2answers
96 views

What misconception about telephone circuits are they trying to address?

I'm reading a book called "Telephony" published in 1905 (Miller,Mcmeen). The book starts with this quote: To properly understand the manner in which sound is transmitted from one end of an ...
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1answer
40 views

How does a video entry system send audio and video, as well as ring/unlock over 4 wires?

I’ve been trying to understand how my door entry system works. Between the monitor/base station and the bell/camera/speaker there’s only 4 wires: 12V DC GND Voice (2 way) Video (1 way) I opened it ...
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20 views

Interface broadcast phone-in console with GSM telephone

I have a broadcast phone-in console with RJ-11 telephone inputs. Since landline telephone line is more noisy and prone to failure, I want to interface a GSM based landline ( with no RJ 11 loop-through ...
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1answer
112 views

Can I extend a single twisted pair DSL line using a coaxial cable?

I'm in the process of setting up a DSL modem/wifi router, which should be connected to a phone line that uses a single twisted pair. However, the phone line enters my house in a slightly inconvenient ...
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0answers
65 views

Are the two wires in a telephone cable swappable?

I am in Switzerland. Our landline is delivered through an unshielded twisted pair cable. Are the wires in the pair swappable ? Or does it have a polarity ? The lines is supposed to provide ADSL ...
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1answer
43 views

Power consumption [duplicate]

A phone charger is rated with input of AC 240v 50/60Hz 0.35 amps will it accept only 240 v 0.35 or will it take full 240 v 16 amps and step it down please I am very new to electrical stuff please help ...
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2answers
83 views

Spiral hoar frost and spiral device around telephone or electric landlines

I live in Germany. When I travel by train, sometimes there are cables that run from pole to pole parallel to the train track. From the lack of insulation between wire and pole, I guess these are ...
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1answer
67 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 ...
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1answer
140 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 ...
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4answers
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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 ...
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4answers
155 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 ...
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1answer
77 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
69 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 ...
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0answers
145 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
247 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
108 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, ...
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1answer
50 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 ...
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2answers
126 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 ...
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3answers
1k 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
2k 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
9k 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: ...
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3answers
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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
389 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 ...
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5answers
138 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 ...
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4answers
5k 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
83 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 ...
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2answers
3k 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 ...
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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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394 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
114 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 ...
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1answer
117 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
123 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 ...
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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
67 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 ...
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1answer
49 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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2answers
156 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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5answers
2k 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
76 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 ...
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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 ...
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1answer
114 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 ...
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1answer
954 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
98 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 ...
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1answer
114 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 ...

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