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Telephone Circuits

Telephone Circuits:   #'s - B       C - F       G - K       L - Q       R - S      T - Z

Last Updated: November 30, 2017 10:28 AM

Circuits Designed by Dave Johnson, P.E. :

Cell Phone Charger -  It seems that as cell phones become more sophisticated, their operating times become shorter and shorter.  If you are on the go all the time and have difficulty finding AC or DC outlets to charge your phone, you might consider this simple scheme . . . Hobby Circuit designed by David A. Johnson P.E.-August, 2009

Cell Phone Solar Powered Charger -  The simple circuit below regulates the voltage from a 6v solar panel to a fixed +5v.  That voltage can be fed to any cell phone or USB connected portable device, to charge its battery.  The circuit uses a Reg113-5 voltage regulator from Texas Instruments . . . Hobby Circuit designed by David A. Johnson P.E.-January, 2011

Cut Phone Line Alarm -  Burglars, rapists and other criminals will often cut a phone line before they break into a home.  The cut phone line will prevent many alarm systems from alerting the police.  The battery powered circuit below will sound an alarm when the unit. . . Circuit by Dave Johnson P.E.-October, 2005

Display RF Signal Strength -  Many cordless telephones, computer networks and cell phones use a RF transmitter lefted on the 2.45GHz band.  Using a microwave diode detector and 100uA meter, this passive circuit will display the strength this signal.  The drawing shows how a bent piece of wire can be used as the antenna. . . . Hobby Circuit designed by David Johnson P.E.-July, 2006

DIY Cell Phone Charger -  It seems that as cell phones become more sophisticated, their operating times become shorter and shorter.  If you are on the go all the time and have difficulty finding AC or DC outlets to charge your phone, you might consider this simple scheme . . . Hobby Circuit designed by David Johnson P.E.-August, 2009

Do It Yourself Portable Cell Phone Charger -  It seems that as cell phones become more sophisticated, their operating times become shorter and shorter.  If you are on the go all the time and have difficulty finding AC or DC outlets to charge your phone, you might consider this simple scheme. . . Circuit by Dave Johnson P.E.-August, 2009

Four Line Telephone Line Status Indicator -  Many home businesses use multiple phone lines.  This circuit gives you a visual indication when a line is in operation.  The two AA battery cells should provide enough power for about one year of operation. . . Circuit by Dave Johnson P.E.-June, 2000

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Differential scope probe Delivers 6-GHz bandwidth to the screen -  02/20/03 EDN Design Ideas:  With digital scopes that offer 6-GHz bandwidth suddenly almost commonplace and with industry participants now recognizing differential signaling as all but essential for sending multigigahertz signals across pc boards and backpla __ Circuit Design by Dan Strassberg

Digisound ring Modulator -  Dual Ring Modulator based on MC1496.  The X and Y inputs are AC coupled and are capable of accepting 10V p-p signals.  Comprises two totally independent ring modulators on the same PCB which produces the sum and difference with two input signals.  ideal for the production of a whole range of sounds including bell and gong sounds __ Designed by dave @ NO_SPAM_digisound80.co.uk 

Display RF Signal Strength -  Many cordless telephones, computer networks and cell phones use a RF transmitter lefted on the 2.45GHz band.  Using a microwave diode detector and 100uA meter, this passive circuit will display the strength this signal.  The drawing shows how a bent piece of wire can be used as the antenna. . . . Hobby Circuit designed by David Johnson P.E.-July, 2006

DIY Cell Phone Charger -  it seems that as cell phones become more sophisticated, their operating times become shorter and shorter.  if you are on the go all the time and have difficulty finding AC or DC outlets to charge your phone, you might consider this simple scheme . . . Hobby Circuit designed by David Johnson P.E.-August, 2009

Do It Yourself Portable Cell Phone Charger -  It seems that as cell phones become more sophisticated, their operating times become shorter and shorter.  if you are on the go all the time and have difficulty finding AC or DC outlets to charge your phone, you might consider this simple scheme. . . Circuit by Dave Johnson P.E.-August, 2009

Door Phone Intercom -  A simple 2 way intercom based on the LM386386 using 8 ohm speakers __ Designed by Laurier Gendron & Andy Collison

DSL Filter (phone-line) -  The above diagram is a standard low-pass telephone line filter (L1, C1, L3, C2).  L2 and L4 are needed since we're dealing with the 'Tip' and 'Ring' of a phone line which may carry up to 90VAC!  __ Designed by Tony van Roon  VA3AVR

DTMF Coder Makes Low-Cost Sine-Wave Generator -  10/13/94 EDN Design Ideas:  A telephone DTMF IC produces, by design, two tones if you connect a single intersection of the IC 's 4[x]4 keypad matrix (Fig 1]. (Telephones commonly have 3×4 keypads but, unknown to many people, the applicable standard allows for a fourth row of four keys.   ]But, if you connect two key inputs at once, the IC produces a single-frequency,  __ Circuit Design by Criscuolo Anna Rita, Labtec Telecommunications, Nichelino, Italy

DTMF Decoder -  Uses MT8870 DTMF decoder and PIC  microcontroller to decode telephone tones.  __ 

DTMF Decoder for PC -  Our DTMF decoder can be powered from a 9V battery or from your parallel printer port.  it can detect and display all 16 DTMF digits on your computer screen in real-time.  The Window's program can be placed in the minimize mode and still detect tones while you use your computer to do other things like Net surfing! ! ! !  We are now in the process of adding an DTMF decoder which will interface to the sound card gameport.  __ 

DTMF Decoder with LCD Display -  The DTMF decoder 2 is a useful tool used for decoding DTMF (Dual Tone MultI frequency) generated by telephones.  The decoded digits are viewed on a 16x2 LCD screen.  __ 

DTMF Generator/Decoder -  The photo depicts a DTMF generator/decoder pair you can build in an afternoon or two.  Dual-tone-multi-frequency (DTMF, also known as touch-tone) are the audible sounds you hear when you press keys on your phone.   The tone generator (top) uses the 5589 chip and a DiP switch.  You can actually hear the tones through the speaker.  The bottom circuit uses the 8870 to decode a tone and display its associated number on the 7-segment LED. __ Designed by Boondog web site

DTMF Radio Remote Control -  Here is a circuit of a remote control unit which makes use of the radio frequency signals to control various electrical appliances.  This remote control unit has 4 channels which can be easily extended to 12.  This circuit differs from similar circuits in view of its simplicity and a totally different concept of generating the control signals __ Designed by Radioland.net

DTMF RECEIVER -  Today, most telephone equipment use a DTMF receiver IC .  One common DTMF receiver IC is the Motorola MT8870 that is widely used in electronic communications circuits.  The MT8870 is an 18-pin IC .  it is used in telephones and a variety of other applications.  When a proper output is not obtained in projects using this IC , engineers or technicians need to test this IC separately.  A quick testing of this IC could save a lot of time in research labs and manufacturing industries of communication instruments.  Here’s a small and handy tester circuit for the DTMF IC .  __ 

DTMF Tone Decoder -  hears touch tones and displays them as telephone numbers __ Designed by Boblick

Dual Band Mobile Jammer for GSM 900 & GSM 1800 -  Undergrad project, Dept Electrical Engineering , Jordan Univeristy of Science & Technology]__ Ahmed Sudqi Hussein Abdul-Rahman and Ahmad Nasr Raja Mohammad

Dual-voltage supply powers SIM card -  01/20/00  EDN Design Ideas:  Global-system-for-mobile-communication phones have a subscriber-identification module (SiM) that allows local wireless providers to recognize the user and his or her billing information.  Although most SiMs are changing to 3V operation, they also accommodate 5V as well during the transition.   __ Circuit Design by Larry Suppan

Duo Phone -  This simple circuit of a duophone allows you to access two telephone lines through one telephone set.  Each telephone conversation will remain entirely separate unless you choose to combine the two...__ Electronics Projects for You

E10-G RS232 Modem -  How to connect a PC RS232 moden to you Pocket PC__ © Vassilis Serasidis

Ericofon installation notes -  To clear up facts about this trendy Ericsson telephone, as well as killing off the myth that these telephones do not contain a ringer.   __ Contact blehack @ yahoo dot com

ErICsson Cell Phone Display GA628 -  The GA628 display provides a 12 character alphanumeric display , some icons in the second line and power consumption of some 100 uA.  it can easily be connected to the hardware, simply by soldering some wires.  The only disadvantage is , it needs a 3.3 V power supply and something around 5.6V.  However, this code and the MSP430 provides a clock for a simple charge pump, realized with 3 diodes __ Designed by Robert Tyrakowski

Extension Phone Line Switcher -  Having multiple extension telephones at home is very convenient.  You can make or receive phone calls practically anywhere in the house.  This circuit disables other telephones connected to the phone line whenever a telephone (either the master or any extension phone) is in use.  The circuit is inexpensive and is guaranteed to keep the phone conversation private.  The circuit does not need an external power supply.  it gets its power from the telephone line.  __ 

Five band graphic equalizer -  This circuit uses a single chip, IC BA3812L for realizing a 5 band graphic equalizer for use in hi-fI audio systems.  The BA3812L is a five-point graphic equalizer that has all the required functions integrated onto one IC .  The IC is comprised of the five tone control circuits and input and output buffer amplifiers.  The BA3812L features low distortion, .  __ 

FM bug 420-480 MHz -  How about getting that old Nokia phone out of your drawer and turning it into something freakishly cool? I will not lie to you, you will need a few tools and skills such as soldering/desoldering and making PCBs.  Here you can download Sprint-Layout__ 

FM Bug-transmitter -  The circuit consists of two separate stages.  The first is an audio pre-amplifier and the second is a 90MHz oscillator.  The first stage is very simple to explain.  it is a self-biasing common-emitter amplifier capable of amplifying minute signals picked up by the electret microphone __ Contact kit is designed and manufactured TALKING ELECTRONICS

FM Telephone Bug -  Receive telephone conversations on any FM radio with this neat little device.   __ Designed by Tony van Roon  VA3AVR

FM Telephone line Bug Transmitter -  Here is a simple transmitter that when connected to a phone line, will transmit anything on that line (execpt the dial tone) to any FM radio.  The frequency can be tuned from 88 to about 94Mhz and the range is about 200 feet.  it is extremely easy to build and is therefore a good, useful beginner project.   __ Designed by Aaron Cake

FM telephone line bug transmitter (88MHz to 94MHz) -  Here is a simple transmitter that when connected to a phone line, will transmit anything on that line (execpt the dial tone) to any FM radio.  The frequency can be tuned from 88 to about 94Mhz and the range is about 200 feet.  it is extremely easy to build and is therefore a good, useful beginner project.  __ 

FM Telephone Transmitter -  Receive telephone conversations on any FM radio with this neat little device.   __ Designed by Tony van Roon  VA3AVR

Four ICs implement video AGC & DC restore -  06/18/98 EDN Design Ideas:  Four IC s--a multiplier, a sync separator, an op amp, and a dc-restore IC --along with a handful of passive components can implement a complete AGC and dc-restore circuit for video signals (Figure 1).  The circuit consists of three main paths  the signal path, the gain-control path, and the dc-restore path.  The input video signalFile contains several Design ideas, scroll to this one __ Circuit Design by Tamara Ahrens and Mike Wong, Elantec Semiconductor Inc, Milpitas, CA   

Four Line Telephone Line Status Indicator -  Many home businesses use multiple phone lines.  This circuit gives you a visual indication when a line is in operation.  The two AA battery cells should provide enough power for about one year of operation. . . Circuit by Dave Johnson P.E.-June, 2000

Fourth-Order Speech Filter (Based On Texas Instruments Application Note) -  Human speech generally occupies an audio spectrum of 300 to 3400 Hz.  There is a requirement, especially in telephone circuits, to limit the frequency response to this range.  The ‘Digital Speech...__ Electronics Projects for You

FSK Modem with PIC16C84 -  schematic only __ Designed by shaunwilson19 @ yahoo.com

Full-duplex doorphone with 3 Wires connection -  This circuit is a two-way (full-duplex) construction planned for use as door phone.  To use, two pieces of the same circuit must be connected together with three wires: MiNUS (ground) , PLUS (power) and LiNE.  One of the circuits must be connected to a stabilized power supply, 6-30VDC __ Designed by Peter Jakab

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Telephone Circuits:   #'s - B       C - F       G - K       L - Q       R - S      T - Z


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