How to trigger a buzzer when countdown reach to 00? where should I connect the base of BC547? Do I need a logic gates?


Joined Mar 31, 2012
If you had that circuit in a box that you couldn't look into, and instead were limited to giving someone a list of specific signals and having someone tell you the voltages of those signals, what signals would you put on the list, keeping in mind that there is value in keeping that list as short as possible.

Thread Starter


Joined Dec 3, 2023
U1-11 and U14 are in conflict. You cannot do that.
actually I did it, I used 2 8 input NOR gate, one is connected to the base of transistor, one si connected to the clock (DN) so when the timer reach 00 from the timer it will send low signal, but with the used of NOR gate. The low signal became high and that triggers the transistor to buzz