Please check the connections of this circuit

Discussion in 'General Electronics Chat' started by dumindu89, Jun 28, 2012.

  1. dumindu89

    Thread Starter Member

    Oct 28, 2010
    113
    0
    Please tell me that the DIP switches connected are connected with the correct way or not.
    I need to give "1" or "0" to each ABCD inputs (as I need) of the each counter using DIP switches.
    If they are not connected correctly tell me how the should be connected.(specially Vcc and GND of DIP switches).

    [​IMG]
     
  2. BSomer

    Member

    Dec 28, 2011
    433
    106
    I think that you need to put in some pull up/down resistors on the inputs. They way you have it, when the switches are on the inputs are "floating". Generally what is done is the inputs are tied to VCC through a 10k ohm resistor. The inputs also connect to ground through the switch. So when the switch is off the input is pulled high through the resistor, when the switch is on the input is pulled low to ground.
     
  3. KMoffett

    AAC Fanatic!

    Dec 19, 2007
    2,576
    231
    74XXX TTL's inputs are "normally" high. You need a pull-down switch or resistor the force a low input. As BSomer said, a pull-up resistor is desirable if the input is left floating.

    Two switching methods (from TTL Cookbook):
    1. 2.2KΩ between input and +Vcc, and switch between input and ground. Switch closed = low
    or
    2. 330Ω between input and ground, and switch between input and +Vcc. Switch closed = high

    Ken
     
    dumindu89 likes this.
  4. dumindu89

    Thread Starter Member

    Oct 28, 2010
    113
    0
    Hi!
    I would like to go with the second method; switch closed = high which is the common one.

    Do you mean the circuit should be as follows (assume resistors are 330 ohms)?
    [​IMG]
     
    Last edited: Jun 29, 2012
  5. KMoffett

    AAC Fanatic!

    Dec 19, 2007
    2,576
    231
    Looks right.

    Ken
     
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