Up counter using D Flip Flops

Discussion in 'Homework Help' started by Yami, Apr 6, 2016.

  1. Yami

    Thread Starter Member

    Jan 18, 2016
    Hi, I'm try to make an up counter using D flip flops. All the Q outputs are connected to a BCD Ic to drive the seven segment display..it doesn't work :(. I tried connecting individual leds to the Q outputs and it counted from 0 - 13 in binary from. Now for some reason it doesn't do that even. I've attached a screen shot of the block diagram of how I have connected my FFs. I might have accidently given 5v to one of the FF Q outputs at one point- may it have damaged the IC (how would I check?). Also I don't really understand the clear and reset pins of the IC. D flip flop IC i'm using is 74LS74AP, for the clock I have a switch connected. Please help!
    Thanks so much
  2. crutschow


    Mar 14, 2008
    Applying 5V to the output could have damaged the circuit.
    Look at all the outputs to see which is not working.

    The clear and preset pins should be tied to +5V.

    Using a mechanical switch for the clock will not work reliably without a debounce circuit to ignore the bouncing contacts when they close. Otherwise the circuit may see multiple clock pulses for each switch closure.
    Yami likes this.
  3. WBahn


    Mar 31, 2012
    Using a chip without understanding what all of the inputs mean, or at least how they need to be configured to use it in the mode that you want, is a recipe for disaster. Get the data sheet for the part you are using and read about each of the inputs.

    Applying 5V to one of the outputs might have damaged the chip. You can test it for basic functionality (which means knowing how it is supposed to function, which involves that pesky datasheet) but even if it appears to function properly the chip might still have been stressed and will fail much more quickly than it otherwise might have.

    How did you apply the outputs to LEDs? Did you use an appropriate current limiting resistor?
    Yami likes this.
  4. Yami

    Thread Starter Member

    Jan 18, 2016
    Yeah I did use 1K resistors. Both of my ICs are dead :( - but only one side is faulty of both the ICs :S.. and there is only one more D-flip flop in the local electronics shop. I think I would have to get two J-K FFs
  5. KaiL


    Aug 30, 2014
    It is hard to know if the IC is faulty or not. Usually you would need a IC tester to check.

    Even though most people dont have IC tester , there are still way to check if it is possible or note.

    Make a simple design using only 1 FF and see if it works the way you want. If not , then yes it is faulty