eelectronics Posted April 21, 2006 Report Share Posted April 21, 2006 anybody please help me find the design equations of the circuit of telephone receiver.It is my minor project to do at my college.I am in a trouble situation.Please help me,please,please.The ringer part is not working also.No ring,dialtone is there,can hear sound through speaker.But the calling person can hear only little of my sound,some problem with mic section,please help me.please,its very urgent.please Quote Link to comment Share on other sites More sharing options...
audioguru Posted April 21, 2006 Report Share Posted April 21, 2006 The ringer part is not working.The ringer in a phone in North America operates on 90VAC/20Hz and with a very low current. Your phone has a DC buzzer that might need a very high current.the calling person can hear only little of my sound,some problem with mic sectionYour mic preamp doesn't have enough gain. Try adding a 4.7uF capacitor across R9 for much more gain. Then the value of C9 will need to be increased to 1uF.You will probably have acoustical feedback howling from the speaker to the microphone. Quote Link to comment Share on other sites More sharing options...
Muhammad Abu Bakar Posted April 22, 2006 Report Share Posted April 22, 2006 I can't see a power supply filter capacitor here. Perhaps T1's function is voltage regulation. However this is the only circuit I have seen w/o a large caps fltr Quote Link to comment Share on other sites More sharing options...
audioguru Posted April 22, 2006 Report Share Posted April 22, 2006 I can't see a power supply filter capacitor here.The schematic on the text page is missing many wires. Download it and you will see that C2 is a big supply filter cap.Perhaps T1's function is voltage regulation.It is the telephone line's current modulator for the mic signal. The zener diode with the big C2 across it is the voltage regulator. Quote Link to comment Share on other sites More sharing options...
eelectronics Posted April 22, 2006 Author Report Share Posted April 22, 2006 audioguru , Please give me some of the design equations.I am in great need of that,please.Also give me some more information about working of circuit.Please.i will be greatful to you,Please,..... Quote Link to comment Share on other sites More sharing options...
audioguru Posted April 22, 2006 Report Share Posted April 22, 2006 audioguru , Please give me some of the design equations. I am in great need of that,please. Also give me some more information about working of circuit.Design Equations won't do any good until you find out the specifications of a telephone:1) The max current of the ringer so you can select an AC ringer with the proper impedance.2) The allowed transmit level on the phone line and sensitivity of your microphone. Then you can calculate the gain of the mic preamp.3) Selection of a speakerphone IC (Motorola make two good ones) to eliminate acoustical feedback howling.4) Selection of a dial circuit.Your circuit is very simple. What working of it don't you understand? Quote Link to comment Share on other sites More sharing options...
Muhammad Abu Bakar Posted April 22, 2006 Report Share Posted April 22, 2006 O.K. I can c my misunderstandings. T1 is Common collector config I Think. Then what is the thing which stops output of T1 again becoming I/P to the IC1. Why current o/p at emitter won't produce voltage at VR1 and hence feed back internally???Audioguru I was thinking of a circuit to have intercom with high mic sensitivity & Loud Speakers, to interconnect two parts of my house. Is it possible? Quote Link to comment Share on other sites More sharing options...
audioguru Posted April 22, 2006 Report Share Posted April 22, 2006 Then what is the thing which stops output of T1 again becoming I/P to the IC1. Why current o/p at emitter won't produce voltage at VR1 and hence feed back internally???Your circuit will have feedback when its mic preamp has enough gain. A hybrid transformer or two-opamps bridge circuit can offer a little amount of separation between the transmitted sound signal and the received sound signal. In addition, speakerphones use press-to-talk switching, "voice switching" or an acoustical echo canceller circuit to reduce feedback.Audioguru I was thinking of a circuit to have intercom with high mic sensitivity & Loud Speakers, to interconnect two parts of my house. Is it possible?Feedback howling is guaranteed unless the calling station switches off its speaker when it is transmitting.This circuit doesn't need switching and might work:http://www.redcircuits.com/Page78.htm Quote Link to comment Share on other sites More sharing options...
Muhammad Abu Bakar Posted April 23, 2006 Report Share Posted April 23, 2006 What is function of SW1?Which Amplifier IC used in ckt? Quote Link to comment Share on other sites More sharing options...
audioguru Posted April 23, 2006 Report Share Posted April 23, 2006 What is function of SW1?It disables the mic preamp so you can't be heard when you want some privacy.Which Amplifier IC used in ckt?It is a little Philips amp (1W with a 6V supply) in the parts list but an LM386 would also work fine and give about 1/4W with a 6V supply. Quote Link to comment Share on other sites More sharing options...
eelectronics Posted April 23, 2006 Author Report Share Posted April 23, 2006 Hi Audioguru, I am new to electronics design.I dont know the working of this circuit and need of each components,please give me as much info as you knowAlso as much design equations you know,please help me. Quote Link to comment Share on other sites More sharing options...
audioguru Posted April 23, 2006 Report Share Posted April 23, 2006 Hi Audioguru, Quote Link to comment Share on other sites More sharing options...
eelectronics Posted April 23, 2006 Author Report Share Posted April 23, 2006 Audioguru, I have already told u that this is my circuit as miniproject,I will not be able to change it.So i want to have maximum knowledge with the given circuit for my exams.So if you are really an electronics god,please help me.Why cant you give me the knowledge you have about the circuit,if it is good for me.As i have told,i am new to the electronics field and have limitted knowledge to design,i took this circuit form some magazine where there was not sufficient information such as design equations and explanation of working.So if you spend some time to explain the a b c d of the circuit,it will be a great help for me.Please,please,please,please,help me. Quote Link to comment Share on other sites More sharing options...
audioguru Posted April 23, 2006 Report Share Posted April 23, 2006 You won't learn anything if I do the work for you.If you just copy what I say like you copied the circuit then if your teacher sees it you will fail.Did you try adding a capacitor across R9 and did it increase the level of the mic? Did it cause acoustical feedback howling? Can you explain to your teacher why the gain increased?Studies for you:1) What is the function of the bridge rectifier made with D1 to D4?2) What is the approximate voltage gain of T2 without adding a capacitor across R9?3} What is the function of R6?4) What is the max undistorted power of IC1?The value of C10 is difficult to read because it looks like a clock. Is it only 330pF?Calculate the highpass filter's cutoff frequency of C10 into VR1.It is a very simple circuit, what do you want to know? Quote Link to comment Share on other sites More sharing options...
eelectronics Posted April 23, 2006 Author Report Share Posted April 23, 2006 ???I have told you many times that i need design equations,still you say you don't know what i want.Thankyou for your info about capacitor.It works.I have some knowledge about circuit.But i want it to be clarified.If you had told me the working from a b c d,i can surely study those things and it will help me for my exam.Actuallt i dont have much time to get texts and study from that.i want to know how the circuit works as a telephone,receiving and sending info ,amplification etc.Ok thank you.I will not disturb you more. Bye,thank you Quote Link to comment Share on other sites More sharing options...
Muhammad Abu Bakar Posted April 25, 2006 Report Share Posted April 25, 2006 Audioguru u mentioned these methods to avoid acoustic feedback/hawling. 1. hybrid transformer 2. voice switching 3. acoustical echo canceller 4. two-opamps bridge circuitKindly give the info about last two techniques and provide circuits of possible.Thank u Quote Link to comment Share on other sites More sharing options...
audioguru Posted April 25, 2006 Report Share Posted April 25, 2006 Audioguru u mentioned these methods to avoid acoustic feedback/howling. Quote Link to comment Share on other sites More sharing options...
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