Comments on: Telephone in use indicator. http://www.circuitstoday.com/telephone-in-use-indicator An Authentic Resource on Electronics Thu, 09 Feb 2012 02:28:13 +0000 hourly 1 http://wordpress.org/?v= By: J.P.Cochran http://www.circuitstoday.com/telephone-in-use-indicator#comment-78269 J.P.Cochran Mon, 23 Jan 2012 14:52:23 +0000 http://www.circuitstoday.com/?p=1233#comment-78269 how Q1 get biased when the voltage gets low? and also Id like to know how the circuit works if I connect end of R4 between R3 and R5 instead of Q2 collector ? how Q1 get biased when the voltage gets low?
and also Id like to know how the circuit works if I connect end of R4 between R3 and R5 instead of Q2 collector ?

]]> By: Techone http://www.circuitstoday.com/telephone-in-use-indicator#comment-9980 Techone Sat, 13 Nov 2010 16:00:03 +0000 http://www.circuitstoday.com/?p=1233#comment-9980 That is a nice circuit. Also a telephone line checker. In North America telephone system, red wire is negative and green wire is positive. ( Use a multimeter ) In-hook ( no phone is pick up ) The tel line content a DC AND AC. DC about -48 to -60, AC is about 90 to 120. On-hook, the DC is -10 V and no AC, just a phone signal ( talk, dial-tone, modem signal ). The circuit simply use the DC part of the phone line. Useful to check the phone line at your home. I don't know about European system or Asia system. That is a nice circuit. Also a telephone line checker. In North America telephone system, red wire is negative and green wire is positive. ( Use a multimeter ) In-hook ( no phone is pick up ) The tel line content a DC AND AC. DC about -48 to -60, AC is about 90 to 120. On-hook, the DC is -10 V and no AC, just a phone signal ( talk, dial-tone, modem signal ). The circuit simply use the DC part of the phone line. Useful to check the phone line at your home. I don’t know about European system or Asia system.

]]> By: prashant http://www.circuitstoday.com/telephone-in-use-indicator#comment-7843 prashant Wed, 23 Jun 2010 18:11:41 +0000 http://www.circuitstoday.com/?p=1233#comment-7843 an red LED should show that user is engaged on phone! and green for free.....thanks in advance an red LED should show that user is engaged on phone! and green for free…..thanks in advance

]]> By: prashant http://www.circuitstoday.com/telephone-in-use-indicator#comment-7842 prashant Wed, 23 Jun 2010 18:10:13 +0000 http://www.circuitstoday.com/?p=1233#comment-7842 hello sir, i need to make a project on similar line but very complex sir....please help.....suppose there are three or more telephone lines for a user, and user wants to attend only one phone at a time (for incoming). As soon as he picks up one line other lines should be engaged for callers(incoming).....but user can do an outgoing from any line while on conversation from 1st line....is this project possible??? plz do reply! hello sir,
i need to make a project on similar line but very complex sir….please help…..suppose there are three or more telephone lines for a user, and user wants to attend only one phone at a time (for incoming). As soon as he picks up one line other lines should be engaged for callers(incoming)…..but user can do an outgoing from any line while on conversation from 1st line….is this project possible???
plz do reply!

]]> By: FRANK http://www.circuitstoday.com/telephone-in-use-indicator#comment-7415 FRANK Thu, 27 May 2010 12:03:27 +0000 http://www.circuitstoday.com/?p=1233#comment-7415 Oh I see thank's guru hehe Oh I see
thank’s guru
hehe

]]> By: seetharaman http://www.circuitstoday.com/telephone-in-use-indicator#comment-7401 seetharaman Wed, 26 May 2010 17:56:25 +0000 http://www.circuitstoday.com/?p=1233#comment-7401 Hi Frank When telephone is on hook (not in use) the terminal voltage will be high (around 50 volts) hence Q2 will conduct green LED will glow. When it is in use the terminal voltage will be less ( around 12 volt), Q2 cannot conduct, Q1 will get the bias, RED LED will glow indicating line is engaged. the terminal voltage is DC, without test instruments we donot know which lead is positive and which lead is negative hence a bridge rectifier is added. Please note R2 also should be 3.3K. Hi Frank When telephone is on hook (not in use) the terminal voltage will be high (around 50 volts) hence Q2 will conduct green LED will glow. When it is in use the terminal voltage will be less ( around 12 volt), Q2 cannot conduct, Q1 will get the bias, RED LED will glow indicating line is engaged. the terminal voltage is DC, without test instruments we donot know which lead is positive and which lead is negative hence a bridge rectifier is added. Please note R2 also should be 3.3K.

]]> By: frank http://www.circuitstoday.com/telephone-in-use-indicator#comment-7393 frank Wed, 26 May 2010 10:40:26 +0000 http://www.circuitstoday.com/?p=1233#comment-7393 Uhm.. Could you tell how it’s really works I’d like to know why the resistor and transistor put in that path and also what is it for ?? Thank’s before hope you’d give some light to this newbie Uhm..
Could you tell how it’s really works
I’d like to know why the resistor and transistor put in that path and also what is it for ??

Thank’s before
hope you’d give some light to this newbie

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