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  1. May 25, 2008 #1
    Hi all

    i need some one to hlep me about ele projects

    i need project with diode and transistor

  2. jcsd
  3. May 25, 2008 #2


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    Welcome to PF!

    Hi khaledhd4! Welcome to PF! :smile:

    Give us some details about your problem. :smile:
  4. May 25, 2008 #3
    Are you serious?
  5. May 27, 2008 #4
    how about turning the led on/off with transistor? led is a diode
  6. May 28, 2008 #5


    i need help for this project
    Last edited by a moderator: May 28, 2008
  7. May 28, 2008 #6


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    Staff: Mentor

    Your SCR is drawn upside-down, I believe.


    The cathode and trigger should be towards the negative terminal of your full-wave bridge rectifier. Do some reading at wikipedia.org about diodes and SCRs (silicon controlled rectifiers). If you still have questions after doing that reading, please post more detailed questions here.
  8. May 28, 2008 #7
    help me

    Doable project Balkotaibat

    This program is aimed at cutting contact on Tel when used the other phone

    Please help and did not understand Vassallo send me because I'm not creative in the English language
  9. May 28, 2008 #8
    and i need some one to tell we

    Telephone line AC or DC ?
  10. May 28, 2008 #9


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    Standard Telephone line is DC with the Ringing voltage AC.

    Your previous post did not translate understandably.
  11. May 28, 2008 #10


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    Can you translate the text for us that appears in the diagram? Do you have any idea why the SCR would be shown backwards? That website appears to have many schematics of portions of circuits -- is it a hobbyist website? Are the circuits supposed to have been tested and proven?

    Here is the datasheet for the SCR shown in the figure:

  12. May 28, 2008 #11
    what ?expline DC with the Ringing voltage AC plaese
  13. May 28, 2008 #12


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    Staff: Mentor

    At least in the US (I am not sure about your country), when the phone is on-hook, there is a 48Vdc potential between the Tip and Ring lines (the two lines of the phone twisted pair cable). When the phone rings, there is a large AC voltage coming down the cable -- I think around 100V peak-to-peak or more (I forget the exact number). When you pick up the phone, the input impedance of the phone drops, and that pulls the voltage down to just a few volts. That is the signal back to the central office to stop the ring signal. When the phone is off-hook, you have something like 10Vdc (again, I forget the exact numbers).

    Here is a link to more info so that you can get the exact numbers:

  14. May 29, 2008 #13
    look my frined
    i need to make aproject for electronic lab
    and i take electronic 1
    i need asmall project to do
    do you have one ?

    I make the project in previos pic

    but when I conect tow telephone
    the curent be low
    I thenk there is aproblem
    can you help me ?
  15. May 29, 2008 #14
    and I need to help me about the circuit
    that can discover where the wier cut



    what do you say ?
  16. May 29, 2008 #15


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    Staff: Mentor

    What can you tell us about the 4069 IC? Have you looked at the datasheet? Which part is the oscillator, and which part is the counter? What do you suppose the output LED is supposed to do?
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