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Please help modified a circuit

Discussion in 'Electronic Projects Design/Ideas/Reviews' started by cannibal, Sep 27, 2007.

  1. audioguru

    audioguru Well-Known Member Most Helpful Member

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    Your counter ICs are old fashioned TTL that need a 5V regulated supply and a 5V input signal. They will blow up with a 9V supply. They have a very low input resistance that stops your other circuit.

    The CD4026 counter iC is new Cmos that works fine from a 9V battery. It has a very high input resistance that won't stop your other circuit. It counts when its input goes high so it needs a transistor as an inverter.

    EDIT: The CD4026 uses a common-cathode 7-segment display.
     
    Last edited: Oct 5, 2007
  2. cannibal

    cannibal New Member

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    so I have to replace which IC with CD4026 counter iC ???

    U1 or U2

    and how the connections will be ???
     
  3. audioguru

    audioguru Well-Known Member Most Helpful Member

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    The 74LS90 is an old TTL counter IC.
    The 74LS47 is an old TTL seven-segment display driver IC.
    The CD4026 does both.

    I was wrong before. The CD4026 can use its Clock Inhibit pin as a low-going counter input. Then a transistor inverter is not necessary.

    Look at its datasheet to see how to connect it.
     
  4. dave

    Dave New Member

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  5. ljcox

    ljcox Well-Known Member

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    That's why I suggested that you use a CMOS device.

    The 4000 series CMOS can operate on a supply voltage between 3 and 15 Volt. So it will work quite happily from the same 9V battery as the 555.

    Also, it uses much less energy than TTL, so your battery will last longer.

    The data sheet shows how to connect the IC. I suggest you draw the full circuit and post it so we can check it for you.
     
  6. cannibal

    cannibal New Member

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    In progress :)
     
  7. cannibal

    cannibal New Member

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    Here it is

    I tried to search for CD4026 IC but too bad I couldn't find it

    need your comments
     

    Attached Files:

  8. ljcox

    ljcox Well-Known Member

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    What is the transmitter part? how does it relate the the rest?

    Resistor R8 is wrong. The brightness of the display will change depending upon how many segments are lit.

    Replace it with a short circuit and insert a 470 Ohm in series with each segment.

    You also will need to insert 100 nF bypass capacitors. One between pins 5 & 10 of U1 and one between pins 1 & 4 of the 555.

    Also, you are powering the 74LS ICs from the 4.5 Volt battery.

    The manufacturers of 74LS series recommend that the supply voltge should be between 4.75 and 5.25 Volt. So your circuit will probably work when the battery is fresh, but it may become marginal as the battery ages. Why don't you supply it from the 5 Volt supply?
     
    Last edited: Oct 24, 2007
  9. cannibal

    cannibal New Member

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    I done what you said
    please check and tell me if I done it right or wrong

    the trasmitter will be 5 volt power supply with 2 laser pointers


    about why I didn't want to use power supply with 5V in receiver is because the shap of the final device will not be near to the main supply
     

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  10. audioguru

    audioguru Well-Known Member Most Helpful Member

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    The minimum supply voltage for an ordinary 555 is 4.5V. Your three alkaline battery cells start at 4.5V but quickly drop to 3.6V then the voltage drops slower down to 3.0V.

    Your old TTL logic ICs need a regulated 5.0v supply to work properly.
    Most ordinary 5V regulator ICs need a minimum input voltage of 7.5V.
     
  11. cannibal

    cannibal New Member

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    Ok now I will use 9V cell

    and as 555 works fine with 9V

    Could you please add in the image a regulated 5V before the TTL IC's to supply
     
  12. audioguru

    audioguru Well-Known Member Most Helpful Member

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    The voltage from a 9V battery is 9V when it is new but drops quickly to 7.2V when it is used. Then its voltage drops slower to 6V.
    Most ordinary 5V regulators need a minimum input voltage of 7.5V.

    A 9V alkaline battery will soon be dead when driving a voltage regulator and the high current of old TTL ICs and the segments of a 7-segment LED display.

    If the 555 uses a 9V supply and drives the old TTL IC then a voltage divider is needed so the 9V doesn't destroy the TTL IC.

    That is why we said to use a CD4026 IC that has an extremely low supply current and works without a regulated supply.
     
  13. cannibal

    cannibal New Member

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    I searched for CD4026 but I couldn't find it
    may be it's not available in my country

    in the some time I don't want to use fixed voltage power supply from the main supply

    could you please tell me how can I make a 5 volts reach the TTL while I am using the 9V battery

    by the way this will be only for showing and testing several times not for daily use, that’s why I don't bother if the 9V battery will die
     
  14. ljcox

    ljcox Well-Known Member

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    You should have used a ceramic capacitor for C4, not an electrolytic.

    Electrolytics have too much impedence to be of any use as a bypass.
     
  15. cannibal

    cannibal New Member

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    and what about C3 ??
    and how can I make a 5 volts reach the TTL while I am using the 9V battery ?
     
  16. audioguru

    audioguru Well-Known Member Most Helpful Member

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    Use a low-dropout 5V regulator for the TTL and the 555. If you can't find a low-dropout regulator then use an ordinary 7805 and replace the battery when the circuit doesn't work anymore.
     
  17. ljcox

    ljcox Well-Known Member

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    Sorry, I forgot C3. Yes, it should be a ceramic also.

    I agree with Audio re the 5 Volt supply.
     
  18. cannibal

    cannibal New Member

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    Could you please see if what I did is right or wrong ?
    and do I have to add something where red question mark is
     

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  19. audioguru

    audioguru Well-Known Member Most Helpful Member

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    Look at the datasheet for a uA7805 regulator. They recommend using a 0.33uF input capacitor. Yours on the receiver has nothing.

    Look at the datasheet for any old TTL IC. The absolute max input voltage allowed is 7V. Your circuit feeds it 9V.

    Insted of using a voltage divider on the input to the old TTL IC then power the entire receiver circuit from the regulated 5V supply.
     
  20. cannibal

    cannibal New Member

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    Hi again

    please check this attachment


    and C5 is electro or ceramic ? its not clear in the datasheet
     

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  21. audioguru

    audioguru Well-Known Member Most Helpful Member

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    A ceramic capacitor is a low impedance up to a very high frequency.

    An electrolytic capacitor is wound around and around like an inductor at high frequencies.

    Some film capacitors are also wound around and around like an inductor.

    An inductor is a high impedance at high frequencies.
    You want a low impedance at high frequencies at the input and output of a voltage regulator.
     
    Last edited: Oct 25, 2007

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