"Do Not Disturb" Telephone Timer -  it takes your phone off the hook and automatically hangs up again after a preset time.  A LED indicates when the phone is off the hook.__ SiliconChip

1 Cell Flashes White LED -  12/11/03 EDN Design Ideas:  Many portable appliances and other products that must operate from a single cell are restricted to working at very low voltages.  it is thus difficult to drive white LEDs that typically have a forward voltage of 3 to 5V.  The ability Design by Anthony Smith, Scitech, Biddenham, Bedfordshire, UK

1 Line Telephone Line Status Indicator -  This circuit monitors one phone line. . . Circuit by David Johnson P.E.-June, 2000

1.5V iPod Microphone -  Works with: 3rd & 4th Generation and the original color iPods.  Does not work with: 1st, 2nd & 5th Generation, nano, minI or shuffle iPods __ Designed by © Scott Mitchell

2.45ghz RF Signal Detector -  This passive RF indicator is made from a few simple parts.  A 100uA moving coil meter is used to display the relative intensity of the RF signal.  This circuit can be used with some cell phones and many cordless telephones. . . Circuit by David Johnson P.E.-July, 2006

2-Line Intercom Cum- Telephone Line Changeover Circuit -  The circuit presented here can be used for connecting two tele phones in parallel and also as a 2-line intercom.  Usually a single telephone is connected to a telephone line.  if another...__ Electronics Projects for You

3.6 Volt (cell phone) LED Battery Meter -  This is a similar circuit to the above and provides a 4 LED bar graph indicating the voltage of a common 3.6 volt Lithium - ion recharable cell phone battery.  The reference voltage is provided by a TL431 programmable voltage source which is set to 3.9 volts where the TL431 connects to the 1K resistor.  The lower reference for the LED at pin 14 is set with the 5K adjustable resistor.   __ Designed by Bill Bowden

300/1200 baud BAYCOM MoDEM (revision & improved) -  Schematic only, no circuit description __ Designed by Guy Roels ON6MU

300/1200 baud BAYCOM MODEM (revision and improved) -  Ham Radio - Modems and Soundcard interfaces __ Designed by Guy Roels ON6MU

4 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 Design by Tamara Ahrens and Mike Wong, Elantec Semiconductor Inc, Milpitas, CA   

4 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

5 Band Graphic Equalizer using a Single IC/Chip -  This circuit uses a single chip, IC BA3812L for realizing a 5 band graphic equalizer for use in hi-fI audio systems.    BA3812L is a five-point graphic equalizer that has all  required functions integrated onto one IC .    IC is comprised of  five tone control circuits and input and output buffer Amplifiers __ Designed by Paul S

56K RF Modem -  This is a prototype of the WA4DSY 56KB RF modem.  it is intended for use on amateur packet radio networks.  The modem generates RF in the 28 to 30 mhz range and requires and linear transverter to convert the signal to a UHF or microwave ham band.  The digital interface is synchronous serial.  The modem supplies TX and RX clocks.  For more details see the various links below.   __ Designed by Dale Heatherington's Ham Radio, Electronics and Robotics Web Site

60-mA Current Source Feeds Telecomm Lines -  12/18/97 EDN Design Ideas:  An isolated 60-mA current source provide as 120V of compliance for use in telecommunication interfaces (Figure 1).  Constant-current line feed provide as dc power for downstream circuitry independent of line length and provide as inherent short-circuit protection.  The key to isolated Design by Kurk Mathews, Linear Technology Corp, Milpitas, CA

7 band graphic eqalizer -  Audio graphic equalizers are very common as commercial products (for Hi-fi, car audio and stage use) but circuits for them are very rarely published.  I didn't design this one but it's really very simple.  The details shown are for a 7 band but the principle can be extended to almost any number of bands - if you can find accurate enough components. __ Designed by Richard Torrens

8 Line Intercommunication using 89c51 -  This project is aimed to make the low cost intercom system by which eight telephone lines can be interfaced with this hardware.  __ 

800 MHz Base Station Chaos Jammer -  Schematic only __ Designed by va3iul

800 MHz Phone Jammer -  Schematic only __ Designed by va3iul

800 MHz Phone Jammer ver.A -  Schematic only __ Designed by va3iul

9 pin (Female) Nullmodem Cable -  Circuit only, no circuit description included.   __ Designed by Tony van Roon  VA3AVR

9600 Baud Packet Radio Modem -  The conventional packet VHF/UHF radio data rate is 1200 baud because all TNCs provide an internal modem for this speed, and the two-tone AFSK audio spectrum suits unmodified voiceband radios comfortably.  However all TNCs can generate much higher data rates, and most FM radios have an unrealised audio bandwidth of some 7-8 kHz or more.  So in many cases 9600 baud radio transmission is entirely practical with them. __ Designed by James Miller G3RUH

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 of 100m from each other, for...__ Electronics Projects for You

A 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

ADSL Modems that Use the LT1886 as a Line Driver Yield Long Reach & Fast Data Rates -  DN240 Design Notes__ Linear Technology/Analog Devices

AeroComm CL4490 Experiments -  Wireless data networking experiments using AeroComm modules and data modems.  __ Amateur Radio circuits from Green Bay Professional Packet Radio

AFSK 1200 Modem Based on PIC16c620 -  Schematic Only__ 

Alarm Phone Dialer with MT8880 & PIC 16F84A -  Just hook this Alarm Phone Dialer up to something you would like to monitor, for example, a high water alarm, low temperature alarm, back window, garage door, etc.  When the system is activated it will call a number of programmed numbers to let you know the alarm has been activated.  This would be great to get alerts of alarm conditions from your home when you are at work.  The microcontroller code is provided on the site.  __ 

Alarm Sounds when Phone Line is Cut -  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 . . . Hobby Circuit designed by Dave Johnson P.E.-October, 2005

Audio Graphic Equaliser -  Audio graphic equalizers are very common as commercial products (for Hi-fi, car audio and stage use) but circuits for them are very rarely published.  I didn't design this one but it's really very simple.  The details shown are for a 7 band but the principle can be extended to almost any number of bands - if you can find accurate enough components. __ Designed by Richard Torrens

Audio-Visual Extra Ringer for Phone -  Many a times one needs an extra telephone ringer in an adjoining room to know if there is an incoming call.  For example, if the telephone is installed in the drawing...__ Electronics Projects for You

Auto Muting During Telephonic Conversation -  Telephone conversation can be made disturbance-free using this simple circuit.  As soon as you lift the telephone handset to converse, the TV, music system or any other appliance that may be...__ Electronics Projects for You

AVR Phone Recorder & Telephony Platform. Part 1 -  This project describes the implementation of a phone line audio and event recorder originally devised for monitoring technical support call center attendants for quality assurance purposes.  Our initial objective was to have a device that digitizes __ Designed by rlocman @ rlocman.ru

AVR Phone Recorder & Telephony Platform. Part 2 -  in the first part we have got acquainted with the device hardware.  Have considered used interfaces and reports and the general principles of work of system.  Device Usage When first turned on, the device tries to initialize the SD/MMC card.  First,  __ Designed by rlocman @ rlocman.ru

Basic FlashLamp Illuminationry for Cellular Telephones/Cameras -  DN345 Design Notes__ Linear Technology/Analog Devices

Build a HamComm Data Slicer -  Until recently many of the ham radio operating modes required specialist equipment that most often had to by build and was exclusive to the task.  Enter the Personal Computer.  The PC made life a little easier for the ham as it was now able to take over some of the jobs that bespoke hardware did.  But it still wasn't quite there yet.  The task of the PC was mainly to be a 'front end' to a now multI capable bespoke box__ 

Build your own 89C51 PABX -  This 89C51 PABX project is basically an eight line intercom from which you can call one to eight numbers.  The 89C51 PABX system also supports dialing and receiving telephone calls.  __ 

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