Discussion in "Electronics" started by    har    Nov 9, 2007.
Fri Nov 09 2007, 07:30 AM
#1
thanks for the reply

actually sir i wanted to do an project on security system with auto dial up circuit which plays the recorded message via telephone. hence i wanted the circuit details and telephone circuitory working fundamentals
regards
Fri Nov 09 2007, 09:20 AM
#2
there is a project using telephone interface in the download section.. take the circuit as reference.. and please do not create duplicate topics
Voice Ineractive System For College Automation project
Sat Nov 10 2007, 06:55 PM
#3
JUST TO REFER HOW TELEPHONE WORKS REFER THIS LINK
http://communication.howstuffworks.com/telephone.htm/printable
and this may also help as add on
This recorder can be connected to the telephone lines just about any place, and no external power source is needed. The tape recorder's 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 there's usually about 50 Vdc across the phone thats divided over R1, R2, and R4, so that Q1's base is negative enough to keep the recorder off. Pick up the receiver, and the voltage drops to 5 V. That leaves not quite-enough voltage on Q1's base to keep that transistor at cutoff, so the recorder begins. Remember to keep your recorder's switch in the on position, and depending on how many people use the telephone, remember to rewind or change tapes occasionally!
Sun Nov 11 2007, 09:15 AM
#4
a ring detector circuit.. might help you

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steve_yu_chan
Wed Apr 23 2014, 12:14 PM
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Wed Apr 23 2014, 11:46 AM
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Wed Apr 23 2014, 09:25 AM
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Wed Apr 23 2014, 02:57 AM
NAD
hi can someone help me write the code to interface an alphanumeric keypad to pic16f877A??!
Wed Apr 23 2014, 02:56 AM
NAD
hi,
kram.ram420
Mon Apr 21 2014, 09:27 AM
Hi.. Please help me to get through microcontrollers..
Sun Apr 20 2014, 05:23 AM
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HELLO. I AM USING 8051 WITH RFID , PASSWORD AND FINGERPRINT.I HAVE SFM 3030 FINGERPRINT MODULE HOW TO INTERFACE IT WITH 8051? DIRECTLY OR EXTRA CIRCUITRY IS REQUIRED?AND HOW TO USE TWO SERIAL DEVICES RFID AND FINGERPRINT WITH ONE 8051?
ExperimenterUK
Thu Apr 17 2014, 01:23 PM
@mba Great .. please do.
Thu Apr 17 2014, 12:27 AM
mba'
like the forum and wish to participate
ExperimenterUK
Wed Apr 16 2014, 04:45 PM
@viniciusheidrun..you should read my comment just before your post
viniciusheidrun
Wed Apr 16 2014, 01:43 PM
I'm doing a drive system with SIM900D modem and microcontroller AT89S52 via sms. I'm having trouble can not generate the. Hex to send to the microcontroller, whenever I compile the error, I'm using MCU 8051 IDE, what should I do so that my system receive sms and perform my task?
ExperimenterUK
Mon Apr 14 2014, 01:00 PM
@Haranadh,bipin chandra etc. Create threads for your questions.
Sun Apr 13 2014, 04:05 AM
Haranadh
we bought HC 06 Bluetooth modem instead of Module ,Can any one help me of using it as bluetooth module since i am doing this project?
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