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?
October 25, 2019
Use 74xx TTL. Its cheap and easy for beginners. First thing is time base. Most accurate is crystal oscilator and divider. Second option could be line frequency 50/60 Hz derived from source. Third solution could be any oscilator i.e. 2 invertors and some RC. It needs ability to measure frequency and tune it up. Then frequency divide up to 5 min pulses. First pulse "forgot" and next pulses will run buzzer.
November 16, 2019
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