Electronic Circuits and electronic circuits, electronic schematics plus an extensive resource for hobbyists, inventors and engineers

DiscoverCircuits.com, has 45,000+ electronic circuits, cross-referenced
into 500+ categories.    We have searched the web to help you find quick design ideas.
We make every effort to link to original material posted by the designer. 
Please let us if you would like us to link to or post your design.

HOME Schematics Index Hobby Corner Dave's Circuits Electronic Resources Contact Info
Imagineering Ezine    Discover Solar Energy Dave Johnson & Associates Faraday Touch Switches



Telephone Circuits

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

Last Updated: December 07, 2017 02:04 PM

Capacitance Proximity Switch
Draws very low power - Ideal for battery-powered applications
6 Models Available - Call 806-368-7747




Links to electronic circuits, electronic schematics, designs for engineers, hobbyists, students & inventors:

Ultra-Low Quiescent Current AF Power Amplifier -  This is an audio power amplifier, similar to what is common in transistor radios and other portable audio equipment.    This circuit however, has an ultra-low quiescent current of about 250uA, due to a unique bias circuit.  I donít even know of a chip that d __ Designed by Andrew R. Morris

Universal Telephone Hold -  Place any phone in your house on holdeven cordless phones.7 pages.  Not available as a kit of parts.  __ Golab.com

Use Amplifier Phono Input as Line Level Input: Inverse RIAA Filter -  The circuit does two functions: signal level attenuation and inverse RiAA filtering.  The signal attenuation is needed to convert the 500 mV signal to 2.5 mV signal.  The inverse-RiAA filtering is needed to make the frequency response of the system flat (same equalization that is used when music is transferred to vinyl in the studio).  The picture __ Designed by Tomi Engdahl

Use Old Telephones as Intercom -  You may wish to use a 12 to 24V battery, like a Gel Cell, since the car power or cheap power wall wart style supply is probably too noisy. You may have to adjust the resistor value (1.2K for 24V). Whatever gets the phones working and does not use more than 30mA total loop current. if you can manage it, get two speakerphone-type phones. Leave them in "speakerphone" mode continuously and pound on the keypad to attract the attention of the other end. __ Designed by Tomi Engdahl

Use Old Telephones as Intercom -  Talking over the phones is easy.  You put DC current through the phone and it transmits and receives audio.  So two phones and a current source (about 25mA) all in series will give you a talking circuit.  A suitable current source can be as simple as a 9V battery and a series resistor whose value is adjusted (with both phones offhook) till about 25mA flows.  You can then bypass the battery and the resistor with a capacitor to couple the audio straight across and get a loud and clear connection __ Designed by Markus Wandel

Vocalize Telephone Number -  02/03/94 EDN Design Ideas:  The circuit in Fig 1 is a simple method of vocalizing the digit number of a telephone keypad, which, for someone visually impaired, provide as heLPFul voice confirmation.  A 75T202 dual-tone multifrequency (DTMF]receiver decodes the  __ Circuit Design by Shwang-Shi Bai,Chun-Shan Institute of Science and Technology, Lung-Tan, Taiwan

Voice Scrambler/Descrambler -  This is a single-inversion voice scrambler/descrambler.  Though no longer useful for police scanners, it would be a fun project for a hobbyist.  it was designed for use on a 9-volt battery, but by changing resistor values proportionately, it could be adapte __ Designed by Andrew R. Morris

Watch-Dog for Telephones -  Most of the telephone security devices available in market are simple but quite expensive.  These devices provide blinking or beeping type line-tap misuse indications.  Quite often they do not offer guaranteed...__ Electronics Projects for You

Watch-Dog for Telephones -  Most of the telephone security devices available in market are simple but quite expensive.  These devices provide blinking or beeping type line-tap/misuse indications.  Quite often they do not offer guaranteed protection against unauthor-ised operation.  A very simple and uni- que circuit of a telephone watch-dog to safeguard subscriber telephone lines against any fraud is described here.  This little circuit keeps continuous watch over the telephone lines and sounds an alarm in case of any misuse.  in addition it transmits a loud tone through the telephone lines to prevent further misuse.  __ 

Wireless Telephone Bug -  Here's a neat little project that will allow you to monitor your phone line as soon as your phone is off hook.  You can use a regular FM broadcast band radio to monitor the conversation.  Just remember, it __ 

Wireless Telephone Eavesdropper Electronic -  The IR transmitter connects to a telephone circuit, and transmits both sides of all telephone conversations to any line-of-sight location, within 40 feet.  No power is taken from the central office, as long as all phones remain on-hook.  The current flows through the phone and back to the central office__ 

Got Designs?
Please eMail
if you want me to link to and/or post your original design Thanks.

      <<<         This is the last page of T - Z 


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


HOME Schematics Index Hobby Corner Dave's Circuits Electronic Resources Contact Info
Imagineering Ezine    Discover Solar Energy Dave Johnson & Associates Faraday Touch Switches


 About Us   |  Advertise on DiscoverCircuits.com   |   Report Broken Links  |    Link to DiscoverCircuits.com  |    Privacy Policy


Copyright  January, 1998 - December, 2017     David A. Johnson & Associates.  All Rights reserved. 


 Linking is ALLOWED but COPYING any content or graphics to your web site is EXPRESSLY PROHIBITED.