2 Line Intercom Cum Telephone
Line Changeover Circuit: |
2 Line Intercom With Telephone
Line Changeover Circuit:
The circuit presented here can be used for
connecting two telephones in parallel and also
as a2-line intercom. |
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56K RF Modem: |
8 Line Intercommunication using
89c51:
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9 Line Telephone Sharer:
This circuit is able to handle nine independent
telephones (using a single Telephone line pair)
located at nine different locations, say, up to
a distance of100m from each other, for receiving
and making outgoing calls, while maintaining
conversation secrecy. This circuit is useful
when a single Telephone line is to be shared by
more members residing in different
rooms/apartments. |
900Mhz 9600bps Link:
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9-Line Telephone Sharer:
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Caller ID:
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Caller ID / DTMF Audio Decoder:
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Caller ID Circuits:
information and circuits for different systems
used USA and Finland |
Caller ID Decoder: |
Caller ID Decoder Part 1:
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Caller ID Decoder Part 2: |
Caller ID Display Service:
Caller ID decoder based on 68HC11, text in
French |
Cell-Phone-Controlled Audio/Video
Mute Switch:
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Chip recorder customizes phone
ringer: 07/25/2002
EDN - Design Ideas / Companies usually purchase
one type of telephone for all employees, which
is understandable, especially if they obtain a
discount for buying in quantity. One ringer
sound for everyone can pose a problem, though,
if the sound of a ringing phone makes a dozen
people pause and look at their telephones.
Equally annoying is the absence of a visual
message indicator.. |
Circuit Detects When A Shared
Telephone Line Is In Use:
01/08/01 Electronic Design - Ideas for Design /
The circuit shown can detect when a shared
telephone line is in use (see the figure). This
is particularly useful when an automated device
wishes to place an outgoing call without
disturbing an. . . |
Circuit Provides Ground-Start
Supervision For Phone Switching:
11/20/00 Electronic Design - Ideas for Design /
Ground start is the primary analog signaling
method used between telephone switches such as
the central office (CO) and a private branch
exchange (PBX). It offers a way to indicate
on-hook and off-hook conditions in a voice
network. There’s one. . . |
Circuit Provides Message on
Disabled Phone Line:
01/20/00 EDN-Design Ideas / PDF contains
multiple circuits - scroll to find the one of
interest / This circuits plays a prerecorded
message into any phone on the line when its
receiver goes off-hook |
Circuit Translates a Law to µ Law:
05/07/98 EDN-Design Ideas / Two common methods
exist to command voice for transmission through
a PCM channel |
Circuit Vocalizes Telephone
Number: 02/03/94 EDN-Design
Ideas |
Clip extracts signal from phone
line: 07/24/03 EDN-Design
Ideas / Using a capacitive-coupled clip, you can
pick up the signal from a twisted-pair or wire
telephone line or from other unshielded analog
lines without piercing the insulation. No line
test can detect the clip's presence, and it
leaves no evidence of having been attached. It
needs no ground return. You can fasten the
small, insulated pickup plates to the opposing
jaws of an alligator clip … |
Contactless Ringer for Telephones:
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Cordless Phone Backup:
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Creating your Own Telephone Ne2
Rk: you can easily
create your own intercom system using two
telephones, a 9-volt battery (or some other
simple power supply) and a300-ohm resistor
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Cut Phone Line Detector:
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Cut Phone Line Detector #1:
Can be used to alarm security system
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Cut Phone Line Detector #2:
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DC / DC Converter operates From
Phone Line: 01/15/98
EDN-Design Ideas |
Detect Loop-Reverse Battery
Conditions On A Telephone Line:
02/18/02 Electronic Design - Ideas for Design /
Equipment connected to the public
switched-telephone network (PSTN) sometimes
needs to detect polarity reversals of the
battery feed. One common application is the
Direct-Inward-Dialing (DID) service that uses
what is termed as "loop-reverse battery. . . |
Detecting a Telephone Ring: |
Digisound Ring Modulator:
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Digital / Standard Phone Line
Tester: make sure
that the line is suitable for modem use and your
PCMCIA does not damage if you plug it in
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Doorphone Intercom: |
DSL Filter (phone-line):
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DTMF Coder Makes Low Cost Sine
Wave Generator:
10/13/94 EDN-Design Ideas |
DTMF Decoder / Logger: |
DTMF Generation With 3.58 MHz
Crystal: National
Semiconductor Application Notes first
published05-Aug-1995 |
DTMF Products for you:
DTMF decoder can be powered from a 9V battery or
from your parallel printer, schematic and
windows demo program, design by Schmidt
Technologies |
DTMF Proximity Detector: |
DTMF Receiver IC MT8870 Tester: |
DTMF Tone Decoder:
hears touch tones and displays them as telephone
numbers. |
Dual Tone Multiple Frequency DTMF:
National Semiconductor Application Notes first
published04-Nov-1995 |
Electronic Dazer:
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ELF Telephone Audio Pickup:
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FM Radio Telephone Bug: |
FM Radio Telephone Transmitter:
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FM Telephone Bug:
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Free Line Indicator Stops
Interruptions:
12/07/00 EDN-Design Ideas / PDF contains
multiple circuits - scroll to find the one of
interest A simple circuit lights an LED, which
indicates whether the line is free (Figure1a) /
PDF contains multiple circuits - scroll to find
the one of interest. Batteries are unnecessary;
the phone line powers the circuit, and an
accumulator saves energy for an "in use"
indication. |
Generate CID / CIDCW Analog
Signals: 12/07/00 EDN-Design
Ideas / PDF contains multiple circuits - scroll
to find the one of interest / A high-speed µP
can generate CID (caller-ID) / PDF contains
multiple circuits - scroll to find the one of
interest and CIDCW (caller-ID-on-call- waiting)
/ PDF contains multiple circuits - scroll to
find the one of interest analog signals at1200
baud FSK between the first and second20-Hz ring
of an incoming call |
Hold Function for Telephone:
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Home Made PBX / PABX:
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Infrared Head Phones:
Using this low-cost project1-can reproduce audio
from TV without disturbing others. In place of a
pair of wires, it uses invisible infrared light
to transmit audio signals from TV to headphones.
FAIR WARNING -- THIS SITE HAS ANNOYING POP UP
ADS. |
Interface Cables for Various Cell
Phones: |
Isolated Telephone Interface:
This circuit allows you to record audio from a
Telephone line into a tape recorder or computer
soundcard. Most of the parts for this circuit
can be scrounged from an old modem, with some
work, it is possible to rewire the modem
circuitry and use the old modem case.
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Laser Telephone Receiver Circuit: |
Line Status Indicator:
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Link Telephone Intercom-DTMF
Version:
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Low Cost PCO Billing Meter: |
Mobile Cellphone Charger: |
Mobile Phone Battery Charger: |
Multipurpose Circuit for
Telephones: This
add-on device for telephones can be connected in
parallel to the telephone instrument. The
circuit provides audio-visual indication of
on-hook, off-hook, and ringing modes. It can
also be used to connect the telephone to a cid
(caller identification device) through a relay
and also to indicate tapping or misuse of
telephone lines by sounding a buzzer.
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Music On Hold for Telephones:
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NCDS Interface Schematic for
Nokia 3110, 8110, 8110i: |
Noise Reduction (Filter) Circuit: |
Nokia 3210 MBUS Interface: |
Nokia 5190 / 6190 Data Cable: |
Off Hook Phone Line Supplies 150
MW: 09/01/94 EDN-Design
Ideas |
Off Line Telephone Tester:
Here is a circuit of an off-line Telephone
tester which does not require any Telephone line
for testing a Telephone instrument. The circuit
is so simple that it can be easily assembled
even by a novice having very little knowledge of
electronics. FAIR WARNING -- THIS SITE HAS
ANNOYING POP UP ADS. |
Old Phones As An Intercom:
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Parallel Telephone With Secrecy
and Call Prevention:
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Parallel Telephones With Secrecy: |
Parallel Telephones With Secrecy:
This system will enable the incoming ring to be
heard at both the ends. The DPDT switch,
installed with each of the parallel telephones,
connects you to the line in one position of the
switch and disconnects you in the other position
of the switch. At any one Time, only one
telephone is connected to the line. To receive a
call at an end where the instrument is not
connected to the line, you just have to flip the
toggle switch at your end to receive the call,
and act as usual to have a conversation. As soon
as the position of the toggle switch is changed,
the line gets transferred to the other telephone
instrument. |
Personal Silent Alarm System:
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Phone "Hold" With Music:
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Phone Broadcaster:
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Phone Busy Indicator:
simple busy indicator, does not meet regulations
of many countries because this circuit draws
excessive continuous current from the ph1-line
even when not active and this can cause problems
with Telephone system |
Phone Hold With Music:
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Phone in Indicator:
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Phone in use:
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Phone In Use indicator: |
Phone In Use Light:
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Phone line indicator: |
Phone Line Monitor: |
Phone Line to Audio:
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Phone Off Hook Indicator:
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Phone Rang Indicator Light: |
Phone to Audio Interface:
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Phone-line-voltage monitor meets
FCC specs: When you
design equipment that interfaces to a phone
line, it is often desirable to be able to
monitor the dc voltage on the line. This ability
can be useful, for example, to determine whether
a line is in use before attempting to go
off-hook and possibly interrupting somebody's
phone call. FCC regulations place strict limits
on the amount of leakage current an on-hook
device can draw from a phone line. |
Playing a Mac through a Standard
Telephone Line: how
to get sound from computer to Telephone line
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Precision circuit closely
monitors –48V bus:
10/17/2002 EDN - Design Ideas / Ever-greater
complexity in communications systems has spurred
a need for power-supply management. POTS
(plain-old telephone systems) obtain power from
–48V supplies backed by arrays of batteries in
central offices and distributed throughout
copper lines. Although nominally –48V, the
voltage on the lines can vary from –40 to –80V,
and the voltage is subject to surges and .... |
:
Here is a tele-remote circuit which enables
switching "on" and "off" of appliances through
Telephone lines. The circuit described here can
be used to switch up to nine appliances
(corresponding to the digits1 through 9 of DTMF
the Telephone key-pad). The Telephone can be
used to switch on or switch off the appliances
also while being used for normal conversation.
FAIR WARNING -- THIS SITE HAS ANNOYING POP UP
ADS. |
:
when the ph1-rings, lights connected to circuit
flash |
:
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Silent Telephone Alert:
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Simple Circuit to Connect
telephone Equipment to Audio Mixer: |
Simple Phone Tap:
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Simple Phone Tap #1:
will record any conversation on any ph1-on same
line, the circuit seems to be a bad design
because it does not provide proper isolation and
has too low DC impedance (can keep you line
off-hook all the Time) |
Simple Telephone Recorder:
This recorder can be connected to the telephone
lines just about any place, and no external
power source is needed. The tape recorders
switch terminals are applied to a pair of
transistors, connected as Darlingtons, that are
used to turn the recorder on and off. When the
telephone is off-hook theres usually about50 VDC
across the phone thats divided over R1, R2, and
R4, so that Q1s base is negative enough to keep
the recorder off. Pick up the receiver, and the
voltage drops to5 V. That leaves not
quite-enough voltage on Q1s base to keep that
transistor at cutoff, so the recorder begins.
Remember to keep your recorders switch in the on
position, and depending on how many people use
the telephone, remember to rewind or change
tapes occasionally! |
Simple Telephone Ring Tone
Generator: |
Smart Ringing Phone Light:
The circuit shown here is used to switch on a
lamp when the Telephone rings, if the ambient
light is insufficient. FAIR WARNING -- THIS SITE
HAS ANNOYING POP UP ADS. |
Soft Musical Telephone Ringer: |
Soft Musical Telephone Ringer:
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Soft On / Off Switch:
Modern electronic equipment incorporate
"push-to-on-push-to-off" switches that do not
make the clicking noise as with old equipment.
An example of this is the power button on a ATX
computer cabinet. Here is a circuit that does
the same. It can be used to turn on/off any
electronic/electrical equipment that operates on
any range of voltages. FAIR WARNING -- THIS SITE
HAS ANNOYING POP UP ADS. |
Substitute Phone Power Supply
Stops Hum During Audio Testing:
06/09/03 Electronic Design - Ideas for Design
/When developing quality devices that interface
with telephone lines, sensitive audio
measurements are sometimes needed. However, both
frequency noise and distortion added by the test
equipment—as well as low-frequency signals
derived from the |
Switched Capacitor IC and
Reference Form Elegant –48 to +10 Volt Converter:
04/24/03 EDN-Design Ideas /PDF contains multiple
circuits - scroll to find this circuit |
Talking Phone Dial Monitor: |
Taxi Phone Automatic Dialler: |
Telephone amplifier: |
Telephone Audio Interface: |
Telephone Autodialler: |
Telephone Call Meter Using
Calculator And COB: |
Telephone Controlled Night Light:
When the telephone rings, or when the handset is
lifted, the night light is turned on and remains
on while the conversation takes place. When the
handset is replaced in the cradle, the light
remains on for about11 s. During standby
conditions, the -28Vdc bias on the phone line
maintains the output of U3 in a high state. When
the ac ring signal is applied to the phone line,
it is processed by the ring detector U1,
producing a negative output pulse at pin2 for
each ring. These pulses trigger U2, causing its
output to become high and the discharge
transistor to turn off. |
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