Author Options:

How do you make a digital counter circuit which counts to 10 minutes, it will rings a buzzer and when it continues to 15 minutes, it will rings a buzzer? Answered

I need to make a digital counter circuit which it counts to 15 minutes for my big project in my campus . When the circuit counts to 10 minutes, it will rings a buzzer. Same when it continues to 15 minutes, it will ring a buzzer again. (the circuit is for public speaking, so the speaker knows that he or she already went speak for 10 minutes and 15 minutes). We weren't allowed to use an Arduino, Microcontroller, PLCs, IC NE555, and a 4000 series CMOS IC but we were allowed to use breadboard, flip flop, decoder and 7 segments display. I'm kinda stuck here and I'm thinking it's impossible to make such a thing. Do you have any idea guys?


The forums are retiring in 2021 and are now closed for new topics and comments.

1 year ago

That is the thing these days....
We evolved to see that "electronics" are no longer just some soldered parts, mostly passive.
These days if someone talks about an electronics project it almost always means the backbone is a microcontroller or computer like the Raspberries.
Let me give you some hints from back in the old days....

Think basic, really basic!
You know what is allowed and that the task is dead simple in theory.
Now stop overthinking and step back - you see it already? ;)
A NE555 or similar is nothing but a fancy flip flop in a single housing.
In the easy way out you would just use two of them and some transistor on the outputs to turn on a buzzer.
Then you realise the buzzer won't stop and you add another timer for this and so on....
Look up how a simple LED blinking or flashing circuit works.
In simple words a capacitor is charged and once full the transistor is getting enough power on the base to turn on.
The LED flash happens through another capcitor and how big this one is or what the supply voltage is, plus the resistor determines how long the flash is - from a ms to hours if you must.
With this basic circuit and the additional info you will find on these website with the circuits you can quite easy replace the LED with another transistor - to turn on an almost identical circuit part for the duration of the buzzing sound.
To get the additional 5 minutes you do the same again with the output signal from the first buzzer.
Once you start drawing the circuit or making it on the computer you will see the many similarities in the stages.
That will give you other great ideas in regards to resetting a flipflop or monoflop ;)
You should end up with a circuit that is suprisingly simple and low in the parts count.

I am unsure however how to display the seconds with just passive elements and transistors.
One or two IC's no drame at all...
Was thinking of using one minute timer(s) here.
Every 60 seconds the flop is reset while activating a transistor (another flop) to display the number on the display.
Means you have the first LED transistor going active and with two more you "switch" to the next number.
If in doubt look up how make a simple LED counter like a LED bar ;)
The transistor for 10 minutes also activates the timer circuit to make the buzzer sound for a second or so, same for the 15 minute one, maybe with a 3 second duration to indicate it is over.
There are counting LED displays available that could be used to cheat but it would mean you have at least one forbidden IC included in the display itself.