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Telephone Circuits, Page 1
Telephone Circuits:   #-A    B-C    D-F     G-N      O-S     T-Z
Last Updated on: Saturday, August 30, 2014 10:28 AM

Circuits Designed by Dave Johnson, P.E. :

  • 2 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. The circuit is line polarity insensitive.

  • 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.  (added 7/06)
  • 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.


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1 Line Telephone Line Status Indicator -  This circuit is similar to the above circuit, but only monitors one phone line.... [Designed by David A. Johnson]
10 Reasons to Upgrade to a 16800 or 16900 Series Logic Analyzer  -  ....application note is....internal Xilinx and....packet level to....buses ...4 3....integrity by quickly....Trace Core) core....Interface, POS PHY....Agilent Application Note  2007-12-03....[App Note]
2 Line Intercom Plus a Telephone Changeover Switch -   circuit presented here can be used for connecting two telephones in parallel and also as a2-line intercom. (added 6/06)
2 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. The circuit is line polarity insensitive.... [Designed by David A. Johnson]
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.  (added 7/06) …. [Hobby Corner Circuit by Dave Johnson]
8 Stage LED VU Meter -  The circuit below uses two quad voltage comparators (LM339) to illuminate a series of 8 LEDs indicating volume level. Each of the 8 comparators is biased at increasing voltages set by the voltage divider so that the lower right LED comes on first when the input is about 400 millivolts or about 22 milliwatts peak in an 8 ohm system. The divider voltages are set so that each LED....(circuit / schematic design added 6/06)
Audio LED VU meter -  Audio level meter circuits are fairly often requested.  The circuit was designed to work with an audio power amplifier which operated off +18v-0v-18v power rails. The actual voltage used is not too critical except that the feedback is referred to the LED chain....[4QD-TEC: Electronics Circuits Reference Archive]
Audio level meter VU Meter -  This circuit uses just one IC and a very few number of external components. It displays  audio level in terms of 10 LEDs. The input voltage can vary from 12V to 20V, but suggested voltage is 12V. The LM3915 is a monolithic integrated circuit that senses analog voltage levels and drives ten LEDs providing a logarithmic 3 dB/step analog display....(added 09/05)
Audio power meter  -  This VU (volume-unit) meter is capable of monitoring and displaying power levels present at the speaker terminals of an stereo audio power amplifier. The levels are displayed in ten discrete steps.  This meter is not designed to give an accurate display of the power levels....LM3915, stereo VU meter ....
Audio VU Meter -  LM324,This circuit uses two quad op-amps to form an eight LED audio level meter. The op-amp used in this particular circuit is the LM324....

Decibel Meter -  The circuit below responds to sound pressure levels from about 60 to 70 dB. The sound is picked up by an 8 ohm speaker, amplified by a transistor stage and one LM324 op-amp section. You can also use a dynamic microphone but I found the speaker was more sensitive. The remaining 3 sections of the LM324 quad op-amp are used as....
Digital volume control (Aaron Cake) -  based on DS1669 Digital Pot IC (added 8/03)
Digital volume control has log taper -  11-Apr-02 Issue of EDN  Digital potentiometers provide a compact and convenient way to attenuate audio-amplifier signals. However, most such potentiometers suffer from at least one flaw  a nonlogarithmic step increment. To avoid this problem, a user must usually step the potentiometer in a nonlinear sequence to simulate a logarithmic taper.... [Design Idea by Doug Farrar, Los Altos, CA]
High Resistance Voltmeter -  ....
High-Resolution Volume Unit Meter Simplifies CD Recording -  06/21/01 EDN-Design Ideas....Digitally recorded music on CDs offers superior quality to that recorded on vinyl records or tape, but most prerecorded CDs have an annoying characteristic  The average volume levels of the recorded signal can vary by as much as 14 dB from disk to....-- [Chester Simpson, National Semiconductor, Santa Clara, CA] EDN is migrating links. This link is not verified.  Search the "title" + "EDN" for new link.
LED Audio UV Monitor -  The circuit is completely conventional, and is based on the application notes from National Semiconductor. The circuit is shown in Figure 1 and as you can see it uses a single IC and a few discrete components. The extra diode (D3) is included to ensure that the DC to the LEDs is almost unfiltered....(added 5/02)
Precision Audio MilliVoltmeter -  Measures10mV to50Volt RMS in eight ranges Simply connect to your Avo-meter set @50µA range....
Sound Level Meter -  One chip replacement for the standard analog meters, based on LM3915 audio level IC.… [Aaron Cake's design]
Stereo VU Meter Circuit -  This is it. It's a STEREO LED LEVEL METER. It's the cheapest and best bar graph display available and best of all, it uses readily available components. You only need a handful of LEDs, 22 transistors, some resistors, diodes and a set of....
Stereo-VU-Meter (simpel)  -  Dieses Stereo-VU-Meter ist sehr simpel aufgebaut und lässt sich einfach an ein Line Audio-Signal hängen. Dann zeigt es den Signalpegel mit 10 Leuchtdioden pro Kanal an. Diese Schaltung hat keinen Verstärker vorgeschaltet, weshalb der....
Volume Control (Aaron Cake) -  based on DS1669 Digital Pot IC (added 8/03)
Volume Control has Log Taper -  11-Apr-02 Issue of EDN   Digital potentiometers provide a compact and convenient way to attenuate audio-amplifier signals. However, most such potentiometers suffer from at least one flaw  a nonlogarithmic step increment. To avoid this problem, a user must usually step the potentiometer in a nonlinear sequence to simulate a logarithmic taper.... [Design Idea by Doug Farrar, Los Altos, CA]
VU & PPM Audio Metering -  circuits using analog needle meters (added 5/02)
VU Meter (spelektoniikka) -  5 led VU meter, in PDF format, includes circuit board, text in Finnish (added 5/02)
VU Meter 3 -  A very simple circuit of indication of level, with 10 Led. Is used the circuit of half-wave rectification of precision round the IC2, with gain one. With switch S1, we can select the indication of Led. The level of entry is 60 mV-1.25 V....
VU Meter Amplifier -  (electronic schematic / circuit added 4/02)
VU Stereo Meter -  This project will indicate the volume level of the audio going to your speakers by lighting up LEDS. The LEDS can be any color so mix them up and really make it look good. The input of the circuit is connected to the speaker ….(added 05/02)
VX2SE -  Voltage-Controlled Solar Engine:This is Wilf Rigter's voltage-doubling solar engine design; very useful for loads that require higher voltage (like those "super-bright" LEDs).  (added 11/05)
3.5 mm or 6.25 mm Stereo Telephone plug -  ….(electronic schematic added 03/08)
3.5 mm or 6.5 mm Mono Telephone plug -  ….(Circuit design added 03/08)
300 baud modem circuit schematic -  La plupart des modems de type Baycom comportent des circuits qui sont devenus difficiles à trouver, surtout si l'on veut pratiquer le packet à 300 bauds. Une alternative consiste à utiliser plusieurs circuits intégrés qui existent encore, et qui, finalement, reviennent moins cher. Cependant....(circuit added 04/05/06)
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.... [Designed by David A. Johnson]
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.…. (added 10/05)
56K RF Modem -  (circuit / schematic added 6/05)
60-mA current-source feeds telecomm lines -  12/18/97 EDN-Design Ideas An isolated 60-mA current source provides 120V of compliance for use in telecommunication interfaces (Figure 1). Constant-current line feed provides dc power for downstream circuitry independent of line length and provides inherent short-circuit protection. The key to isolated.... [Design Idea by Kurk Mathews, Linear Technology Corp, Milpitas, CA]
8 Line Intercommunication using 89c51 -  ….... [Site is under construction right now]
9-Line Telephone Sharer -  ....
9-pin null modem cable -  Circuit only, no circuit description included…. [Tony van Roon's circuit]
ADSL Modems that Use the LT1886 as a Line Driver Yield Long Reach & Fast Data Rates -  DN240  Design Notes (Linear Technology) (app note added 1/06)
Advances in High Speed Design in Dispersively Attenuating Environments Circuit Boards & Cables -  ....deals with advances made in methods for....aiding the design and analysis of high performance digital....through dipersively attenuating paths.  Agilent Application Note 2002-04-10   (app note added 06/06/06)
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. ….(design added 11/08)
AN-1034: An Optimized DCE Interface for V.34 Modems using the DS8933 & DS8934 Line Drivers & Receivers -  National Semiconductor Application Note  (app note added 2/06)
AN106 Quick CS6420 Speakerphone Interface -  (app note added 6/07)
AN-214: Ground Rules for High Speed Circuits -  AN-214 Analog Devices Application Notes....[App Note]Layout and Wiring Are Critical in Video Converter Circuits.
AN237: TCP/IP Library Programmer's Guide -  Silicon Labs Application Notes....[App Note]
AN-347: Shielding & Guarding -  AN-347 Analog Devices Application Notes....[App Note]How to Exclude Interference-Type Noise. What to do and Why to do it-A Rational Approach
AN-444: Single Chip Modem Provides Low-Cost Data Communication -  National Semiconductor Application Note  (app note added 2/06)
AN-466: Improving the Performance of a High Speed PBX Backplane -  National Semiconductor Application Note  (app note added 2/06)
AN-521: Dual Tone Multiple Frequency DTMF -  National Semiconductor Application Note  (app note added 2/06)
AN-666: DTMF Generation with 3.58 MHz Crystal -  National Semiconductor Application Note  (app note added 2/06)
AN-772: A Design & Manufacturing Guide for the Lead Frame Chip Scale Package -  AN-772 Analog Devices Application Notes....[App Note]
AN833: Microchip TCP/IP Stack Application Note -  Microchip Application Note Published 6-Mar-02  (app note added 2/06)
AN854: Connecting a Picmicro® MicroController to a Standard Analog Telephone Line -  Microchip Application Note Published 21-Aug-02....[App Note]
AN-D27: DMOS Devices for Telecommunications -  Supertex Semiconductors  (app note added 2/06)
Assorted telephone circuits -  several circuits here, spend some time and view each of them
Audio Graphic Equaliser -  Simple 7 band eqalizer (diagram added 2/07)
Audio Visual Indicator for Telephones -  Many a times one needs an extra telephone ringer in an ad joining room to know if re is an incoming call. For example, if  telephone is installed in  drawing room you may need an extra ringer in  bedroom. All that needs to be done is to connect  given circuit in parallel with  existing telephone lines using twin flexible wires.  This circuit does not require any external power source....(added 10/05)
Audio Visual Ringer -  Many a times one needs an extra telephone ringer in an adjoining room to know if re is an incoming call. For example, if  telephone is installed in  drawing room you may need an extra ringer in  bedroom. All that needs to be done is to connect  given circuit in parallel with  existing telephone lines using twin flexible wires.  This circuit does not require any external power....(added 10/05)

Telephone Circuits:   #-A    B-C    D-F     G-N      O-S     T-Z

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