Countdown Timer with buzzer using 74xx ICs

Discussion in 'Homework Help' started by Art_bits, Feb 4, 2016.

  1. Art_bits

    Thread Starter New Member

    Feb 4, 2016
    Hi guys! Can any one help me how to make a countdown clock timer (MM:SS) ..
    We have a project that has to create a countdown timer with buzzer, but I don't have enough knowledge about doing such things that's why I'm seeking for your help...
    The timer can be set for xx min. For example 90 mins and press start. It has to count down from 90 to 0 and trigger an alarm after 90 mins for 1 minute.
    4 seven-segment (2 for Minutes and 2 for Seconds), and a button to set the time
    Stop, Reset Buttons,
    an LED will turn on when the count reaches 0:00

    Using any 74xx family chips IC and other ICs.. I need schematic for this!...
    Thanks in advanced!
  2. absf

    AAC Fanatic!

    Dec 29, 2010
    You can start with 74LS190 up/down counter, then 74LS47 BCD to 7-Seg decoder then to a common anode 7-seg display LED.

    Google for the above datasheet and start designing.

  3. atferrari

    AAC Fanatic!

    Jan 6, 2004
    Maybe you could look at the 74LS292 as well .
  4. WBahn


    Mar 31, 2012
    Your specs aren't complete.

    It's one thing to say, "a button to set the time," but that give no information about HOW that button is supposed to be used to set the time. Lot's of alternatives there.

    What happens when you press "Reset"? Does it go back to the start time that was previously set in it?

    You talk about an alarm in the text but your requirements only talk about an LED. Is the LED the alarm?

    Finally, you say that you need a schematic for this. Apparently you aren't willing to put forth any effort on your own and just want someone to do your work for you. If that's not the case, then YOU need to show YOUR best attempt to solve YOUR homework problem.
  5. Art_bits

    Thread Starter New Member

    Feb 4, 2016
    Never mind the LED and reset button. I already created a basic countdown that starts from 99 - 0 minute (I will not include the seconds anymore). Can someone help me with the continuation of this simulation. I want to know how could I limit the countdown starting from 60 min to 0, where to put the start/stop button and the buzzer that will alarm when the counter hits 0?
  6. Papabravo


    Feb 24, 2006
    The way to start at another value for the countdown is to "load" the counter with the desired value. Read the datasheet carefully and notice the combination of control signals that will cause the values on the "D" inputs to be loaded into the counter. The value on the "D" inputs can be hard wired or controlled by some switches that switch each "D" input between logic "0" and logic "1".

    So what's up with the unconnected input? You know in logic design it is a bad bad thing to have unconnected inputs.