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Can anyone help with my 30 second loop automatic count-up timer problem with IC 555 and 4026 with 7segment cathode not automatically counting? So far it still needs to be manually pressed from button to register a number going up to 99. Any help would be appreciated.

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winny
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Dusky Fuentecilla
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1 Answers1

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It looks like you have the 555 set up for monostable mode. You need to set it up for astable mode.

In monostable mode you have to supply a trigger pulse every time you want an output pulse, this is used to get a fixed width pulse from an arbitrary width trigger pulse.

In astable mode the timer re-triggers itself, so it continuously outputs pulses. This is what you need if you want to use it as a clock source.

If you want it to count 30 seconds from when the button is pressed you're going to need more circuitry. You would need an astable source of 1 second pulses and a monostable source of a 30 second pulse. You would have to have the 30 second pulse enable the timers to count the 1 second pulses. So you would push the button, the 30 second timer would start, and the counters would count the 1 second pulses until the 30 seconds times out and then it stops counting.

There are other ways to do it, you can have the timer start counting and detect a count of 30 on the outputs to make it stop, but that gets into more complicated circuits.

GodJihyo
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  • Thank you for replying and explaining! Now I see, I'm still new to both modes and was unable to put it back last night, but may I ask, what would be the procedure if I were to limit the 7segment to 30 seconds after putting it back to astable mode? – Dusky Fuentecilla Jul 07 '22 at 13:55
  • @DuskyFuentecilla I had just updated it to address that before I saw your comment. You can use two 555 timers, one would have to be 30 seconds and getting accurate timing at that length of time might require a different circuit. I posted about that a while back, I'll see if I can find and link it. – GodJihyo Jul 07 '22 at 14:04
  • Oh, okay, great explanation, thank you for the time to explain everything! The link would be very appreciated as well :D – Dusky Fuentecilla Jul 07 '22 at 14:11
  • @DuskyFuentecilla Here are two links. To get a long delay with a 555 without using a large value electrolytic cap you can use a small film cap and charge it with a current source. https://electronics.stackexchange.com/questions/608349/send-current-to-led-only-after-a-specific-duration/608355#608355

    https://electronics.stackexchange.com/questions/623761/how-to-design-a-circuit-that-will-trigger-after-a-specific-delay-once-a-push-but/623813#623813

     – GodJihyo Jul 07 '22 at 14:42