Desperate help needed with circuit diagram

Discussion in 'The Projects Forum' started by Manghameister, Jan 9, 2009.

  1. Manghameister

    Thread Starter New Member

    Jan 9, 2009
    3
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    I am a complete electronics amateur, literally, i can barely even rewire a plug, but I desperately need help with this circuit. Its a counter circuit that simply adds one on with every pulse from a clock, however when i added in an SPST switch all of the counters and decoders blew up saying that the voltage had gone 6V over the limit. Any ideas would be very welcome.
     
  2. mik3

    Senior Member

    Feb 4, 2008
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    If I am right 74HCXXX logic family needs 5V for the supply voltage. Thus you can't apply more than 5V at their inputs.
     
  3. Alberto

    Active Member

    Nov 7, 2008
    169
    36
    Mik3 is right, you should use 5 volts not 6Volts! Use a 7805 and a 9 volts battery.

    Then you must add a 10K resistor and 100 nF capacitor from the common of every switches to ground, to avoid to mess up every thing when you use the switches.

    Have you grounded all the unused inputs of 74hc00 ? (From your schematic there must be two unused)

    pin 5 of 74hc4511 must be connected to ground

    Pin 5 of 74hc190 must be pulled up with a 10k resistor

    Never leave TTL inputs floating!

    Alberto
     
    Last edited: Jan 9, 2009
  4. mik3

    Senior Member

    Feb 4, 2008
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    Was the circuit working before adding the switch?
    Which switch is it?
     
  5. SgtWookie

    Expert

    Jul 17, 2007
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    Actually, it's never leave CMOS inputs open.

    Tie unused inputs to either +V or GND.
     
  6. bertus

    Administrator

    Apr 5, 2008
    15,647
    2,346
    Hello,

    The 74HC family may work from 2 to 6 Volts.

    The quote comes from this page :
    http://www.kpsec.freeuk.com/components/74series.htm

    Greetings,
    Bertus
     
  7. Manghameister

    Thread Starter New Member

    Jan 9, 2009
    3
    0
    @mik3

    The problem occurs when I place an SPST switch in the left hand corner next to the power supply. I've attached a zip file that has a JPEG picture of the circuit that has slightly changed and the original file. Unfortunately it's in the format of a crocodile technology file so apologies in advance.
     
    Last edited: Jan 12, 2009
  8. SgtWookie

    Expert

    Jul 17, 2007
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    I've extracted the schematic and attached it.
    If you can, please use .PNG format files, as .JPG is a "lossy" format while .PNG is not. .PNG images are much easier to view as a result.

    I don't know what that item is to the left of IC6b (NAND gate, upper left).
    It looks like it's shorting out the battery the way it's placed.

    Also, in logic circuits, it's more typical to have a power switch in the + supply rail rather than the ground rail.

    You still have a lot of inputs that are not connected to anything. Connect them to ground or +V.
     
  9. mik3

    Senior Member

    Feb 4, 2008
    4,846
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    I can say the same Sgt. The battery will blow when you close the switch. What is the problem Manghameister?
     
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