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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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55 votes
10 answers
12k 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 ...
andre314's user avatar
  • 1,006
36 votes
8 answers
8k 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?
Sean Moriarty's user avatar
31 votes
4 answers
6k views

How were four wires replaced with two wires in early telephones?

In this video, when A wanted to talk to B, a microphone was connected to a distant speaker using two wires (A → B). When B talked to A, a copy of above was used in the other direction (B → A) using ...
across's user avatar
  • 1,150
28 votes
7 answers
19k views

Why do PBX systems use -48 V?

It seems common that PBX and other telephone hardware use a positive-ground power supply, where the "hot" line is at -48v. What's the reason for that?
Carl Raymond's user avatar
  • 2,580
24 votes
4 answers
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. ...
user16307's user avatar
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21 votes
6 answers
9k views

Cell Phone as Microcontroller

I have a couple of cell phones laying around, one of them being this one: http://www.gsmarena.com/sony_ericsson_elm-3057.php Is possible to clear the flash memory and replace it with a bootloader and ...
Harry Svensson's user avatar
18 votes
3 answers
3k views

How does a UK analogue telephone detect that the caller has hung up (disconnected)? [closed]

Scenario This is a question regarding the design of UK analogue telecommunications equipment and the consequent design impact that is necessary for a router duplicating those signals. It is asked so ...
user2834566's user avatar
17 votes
6 answers
15k views

Unplugging a router from the wall socket

When the internet appears to have crashed, the service provider invariably gives this advice as a first line remedy: unplug the router from the wall socket, then wait 5 minutes, then plug it back in. ...
Gayot Fow's user avatar
  • 273
13 votes
2 answers
25k views

How does a signal travel down a telephone wire?

Supposing a computer gets data over telephone wire, it has to send/recieve signals, but how do things work? Does it use analog signal or a digital bits? How does it send/recieve "1"s and "0"s?
cursious10's user avatar
13 votes
4 answers
42k views

Wiring up old phone ringer to arduino

I just obtained an old rotary phone at a garage sale. I am working on hooking it up to an arduino project, and I was able to get the dial and hook switches figured out pretty easily. I cannot really ...
captncraig's user avatar
  • 2,054
13 votes
5 answers
10k views

Control the hardware of an old phone using a Raspberry PI

I have a very old phone (60 years old) and I want to control its part using a Raspberry PI: Microphone & speaker from the head set The bell The dial wheel I have the electric circuit but don't ...
Besi's user avatar
  • 737
12 votes
1 answer
1k views

Could someone help me understand this simple circuit?

This is a single-wire earth-return telephone system used in cave rescue communications. simulate this circuit – Schematic created using CircuitLab The ground is a metal casing to make contact ...
Jake's user avatar
  • 255
11 votes
3 answers
4k 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 ...
Tripola's user avatar
  • 733
11 votes
4 answers
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 ...
Sedumjoy's user avatar
  • 729
10 votes
4 answers
332 views

Why are modern telephone lightning arrestors less prone to (rectification) RFI problems than old ones?

I was reading about telephone lightning arrestors in my ARRL RFI Book (first edition, copyright 1998), in chapter 9 "Telephone RFI" (by Pete Krieger, previously WA8KZH, now K8COM) and on page 9.6, the ...
MicroservicesOnDDD's user avatar
10 votes
1 answer
23k views

How do I connect an Arduino to a landline?

How do I connect an Arduino to a landline telephone wall outlet? I'm thinking of home automation, something like: I call my house, and after a few rings the Arduino picks up the phone The Arduino ...
davidcary's user avatar
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9 votes
1 answer
3k views

Phone disassembly: what's that part for?

I replaced a broken screen for a Moto G (1st generation), and now I'm struggling with 'ghost inputs/ghost touches'. In order to track down the problem, I came across a part which is located between ...
user236012's user avatar
9 votes
1 answer
2k views

Question about old telephones (late 70's - early 80's)

This question refers to old landline telephones that would have been used in households in Sweden in the late 70's and early 80's. I would think that this was probably similar to phone technology used ...
x457812's user avatar
  • 201
8 votes
3 answers
2k views

Disable ring on land line phones

Years ago I bought a device at Radio Shack that disabled ringing on household phones. It was a very small box with a modular receptacle on one side, a pigtail on the other with a modular plug, and a ...
Roger's user avatar
  • 81
8 votes
2 answers
6k views

Make old telephone ring

I recently found one of those old rotary dial telephones in my garage and amazingly it still is fully functional (I tested it by hooking it to the phone line). As I have no use for it as a telephone ...
user1371019's user avatar
7 votes
6 answers
7k views

Can lightning strike into the phone line damage electronics in the house through the ADSL modem?

I was always wondering about the following: If lightning strikes directly into the phone line outdoors, can the excess power coming from the phone line jump over the switching power supply of the ADSL ...
adamsfamily's user avatar
7 votes
3 answers
2k views

Connecting two phone handsets to talk

I am hacking some old phones into my arduino project. I am currently controlling all of the ringers, dials, and hooks through my board. At a certain point, I would like to connect the two handsets ...
captncraig's user avatar
  • 2,054
7 votes
3 answers
8k views

Answering landline calls with an Arduino

How can I connect an Arduino to a phone line such that, when a call rings, the Arduino will 'answer' and be able to respond with (touch) tones and, if possible, 'hear' touch tones as well for 2-way ...
aaazalea's user avatar
  • 205
6 votes
4 answers
2k views

Testing a phone cable length

This story must be quite familiar: From the start, I've had a problem with my phone/ADSL line: Cracks, hisses and other noise on the phone - enough to make it occasionally unusable, along with an ...
thkala's user avatar
  • 169
6 votes
4 answers
4k views

How was the first overseas phone call possible back in 1927?

I was watching the Peaky Blinders TV Series when something triggered my curiosity: If there were no satellites, nor underseas cables, how come the characters were making overseas phone calls? After ...
Charley R.'s user avatar
6 votes
3 answers
2k views

Software based Caller ID project- Problem with getting caller ID signal

Nowadays, I am trying to make a Caller ID project without using Caller ID ICs. Firstly, I have done a lot of research in Google to get information of phone lines and their electrical properties. I ...
Ebubekir Çağrı Şen's user avatar
5 votes
4 answers
26k 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 ...
userSteve's user avatar
  • 159
5 votes
3 answers
7k views

How to draw current from a telephone line?

My landline phone comes with a lcd display caller id and clock. Even if I remove the 2 AA 1.5V batteries, the lcd still shows time even if I'm not busy on a call. The lcd has no other source of power ...
quwuwuza's user avatar
  • 317
5 votes
2 answers
892 views

Can anyone identify this phone PCB?

Can anyone identify this mobile phone? http://www.adafruit.com/blog/2010/10/29/what-is-that-electronic-thing-from-yemen/ http://www.flickr.com/photos/ladyada/5126516011/ http://www.bunniestudios....
5 votes
2 answers
2k views

Is it just me, or is charging via usb not as good as using an outlet?

I used to charge my phone during the day at work with a USB cable (plugged into my workstation). Obviously USB doesn't provide the same amount of juice as an outlet so it took all day to charge but ...
DustinDavis's user avatar
5 votes
2 answers
4k views

How can I locate items from a phone? RFID?

I'd like to be able to put something small on items (eg glasses, car keys, etc) and have an Android or iPhone app that will tell me the direction or proximity of a certain item. Current phones usually ...
Loren's user avatar
  • 153
5 votes
2 answers
543 views

Door phone audio signal to pc soundcard

I need to interface door phone system to a pc soundcard to listen and talk to the external unit. The door phone to interface is an as yc/200 of BPT and its a classic analog 4+n wires Door phone ...
Zipporobotics's user avatar
4 votes
7 answers
4k views

What do you call the yellow and black conductors in domestic telephone wire?

Any wannabe telco guy can tell you that the green and red pair are called "tip" and "ring" respectively, most can tell you the historical reason why. That's not what I'm looking ...
Burt_Harris's user avatar
4 votes
3 answers
643 views

Why is speech malformed when listening to a USB signal with an LSB receiver?

When you listen to an LSB (Lower Side Band) signal with your radio set to USB (Upper Side Band) or vice versa, the speech you hear is malformed. What causes this behaviour?
user avatar
4 votes
2 answers
10k views

Phone line to 3.5mm audio line

I need to splice out the audio feed from the hand set line (4P4C jack) to a 3.5mm audio port on a computer to interoperate the call via speech recognition. I do not meddle around too much with analog ...
jakebird451's user avatar
4 votes
2 answers
1k views

Extracting speaker, microphone and hook signals from a two-line telephone

My aim I'd like to use a 'normal' telephone as an audio and switch interface for a project. I want to design a circuit that has the telephone A and B wires on one side (ie. an RJ-11 socket) and has ...
JP.'s user avatar
  • 624
4 votes
1 answer
6k views

How does a telephone hybrid transformer work?

Suppose the following circuit: I can see how an incoming signal (Kim's voice) wouldn't be coupled with the lower pair, but I can't see how an outgoing signal (Ron's voice) only goes through the lower ...
4nt's user avatar
  • 354
4 votes
1 answer
462 views

telephone hold-on music

Can someone explain the following telephone hold-on music circuit in throughout manner because I am still learning how to simulate circuit using gnucap? When TR2 does not conduct, it switches off TR3 ...
kevin998x's user avatar
  • 413
4 votes
2 answers
3k views

What is the difference between a T-Carrier and a Digital Signal?

If you take a look at a digital transmission hierarchy for a telephone network or some data provider, you can see the terms T1, T2, T3 (Tx) and DS0, DS1, DS3 (DSx) used interchangeably. Is there any ...
Ci3's user avatar
  • 815
4 votes
5 answers
1k 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 ...
TheEnvironmentalist's user avatar
4 votes
1 answer
2k views

Tool to test analog phone line connection quality

An ancillary job of mine is to support an analog phone line for our credit card machine. From time to time AT&T changes out hardware in the core which causes the machine's modem to not connect ...
steampowered's user avatar
4 votes
1 answer
443 views

Wireless telecom system (cellular with Erlang and spectral efficiency)

We have a spectrum of 20MHz that we will use on a wireless cellular system, which requires 50kHz per channel. The system is using cluster size K = 4 and the radius of every cell is R = 1 km. a) ...
Thm. Z.'s user avatar
  • 41
3 votes
6 answers
2k views

Connecting landline to soundcard

I'd like to connect my landline tellephone to my computer's soudcard, and I was about to do this when somebody warned me that the voltages are all wrong and that I will blow my soundcard. To what ...
Stefan's user avatar
  • 249
3 votes
4 answers
1k views

SIM card for SMS messaging application. Just pay per text (SMS) rather than monthly fee? [closed]

I"m working on an app that uses text messaging (SMS) in an embedded application and I'd like to source a SIM card where I just pay per text (dont really care about the rates) but I refuse to pay a ...
Seidleroni's user avatar
  • 1,684
3 votes
3 answers
337 views

Is telephone and LAN wiring symmetrical?

Is telephone and 10/100 MBps LAN wiring electrically symmetrical? I mean is it allowed to swap wires in the pairs, or is one of them like GND so they cannot be swapped? It's important to know when I ...
Al Kepp's user avatar
  • 3,001
3 votes
3 answers
822 views

What electric part is on this manhole cover?

Here's a photo of a manhole cover The letters form the word "ТЕЛЕФОН" ("telephone" in Russian in ALL CAPS). What is on the picture in the center? Perhaps it is some part that should be associated ...
sharptooth's user avatar
  • 12.5k
3 votes
3 answers
4k 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, ...
KolonUK's user avatar
  • 133
3 votes
4 answers
49k views

How to create a multi-extension intercom system using wired phones?

I want to create a simple (telephone based) intercom system in our new house. Shouting between rooms is not so good, and trying to use an IM client or Facetime doesn't have the immediacy of a good ...
Piku's user avatar
  • 151
3 votes
1 answer
35k views

Mobile/Cell Phone Power consumption?

I'm trying to work out the amount of watts my mobile phone uses and thus how much power it needs to charge back to full power. My handset is the Nokia 820 Lumia and the specs are as follows: Battery 3....
Ads's user avatar
  • 41
3 votes
3 answers
195 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 ...
InterLinked's user avatar

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