555 timer design

Discussion in 'The Projects Forum' started by Katherine1, Mar 2, 2013.

  1. Katherine1

    Thread Starter New Member

    Mar 1, 2013
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    Hi everyone.. I'm sorry if i ask my ques here since i'm unable to post in the new thread (idk y)
    I wanted to come up with a circuit that acts as a reminder. The general concept is that when I turn ON the switch, the timer will be triggered. After selecting the time interval, timer starts to coundown and a buzzer will beep to remind me that my time is up. I have to turn OFF the switch or else the buzzer will remain beeping.

    I intend to use a 555 timer, piezo buzzer,9V battery and microswitch.
    The time interval is set to 15mins, 30 mins and 60 mins (3 different buttons)

    My problems are,
    1. Is 555 timer able to run up to 60 mins?
    2. How should I connect the resistors and capacitors in order to obtain the time I wanted?
    3. Is there any similar diagrams that I can refer to?

    Thank you for any helps and sorry for any mistakes because I am new to electronics and circuit.
     
  2. Dodgydave

    Distinguished Member

    Jun 22, 2012
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    Last edited: Mar 3, 2013
  3. Wendy

    Moderator

    Mar 24, 2008
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    I typed a full answer last night, and then the site crashed. Opps. So here goes again.

    I'm one of the guys who love the 555 around here. I helped a user named brozizds with a project that sounded much like yours, you ought to review some of his threads.

    http://forum.allaboutcircuits.com/search.php?searchid=4826609

    Count down is a bit of a misnomer, since that implies digits and a display, something you will not get with a 555. I did have a circuit that used bargraph displays to show you approximately where in the timing cycle the 555 was.

    I have also written quite a few articles here on the nifty little chip...

    Bill's Blog

    555 Monostable

    While I don't give private tutorials, if you have a question or need specific help post it publically then send me a PM pointing to the URL.

    Be sure not to try to highjack a thread, this is against the rules. Instead, point to the thread you have a question about and take it from there on your own thread.
     
  4. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    A 555 can reach 1 hr., requires a low leakage cap of around 3600 μF & 1 meg resistor; best I could do was about 3 hr. There may be better solutions.
     
  5. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    Take a read through This thread for a solution involving a PICAXE microcontroller, very accurate timing (+/- hundredths of second). The display is optional. Total parts cost is $25-ish (including programmer and development). Could be less.

    Code is essentially free if you use what is posted in other thread.
     
  6. Katherine1

    Thread Starter New Member

    Mar 1, 2013
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    Actually I don't wish to use a microcontroller. just a simple circuit bcoz my target user is for poor vision elderly(thats y I don't want to have lcd display, but audio signal only) , so i want to keep things as simple as i could.

    Bernard, u had done for 3 hrs? That's great. But 1 ques, how long can the circuit last for to maintain its accurate timing? I want to use this designed circuit for a month only.
     
    Last edited: Mar 5, 2013
  7. tracecom

    AAC Fanatic!

    Apr 16, 2010
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    With your requirement for pushbutton operation and three different time periods, I think your best option would be for three NE555 one shot circuits, each with the appropriate RC timing pair. The accuracy of a NE555 at times up to 60 minutes is not great, but can be fairly close. How accurate do you need it to be, e.g., 60 minutes plus or minus how many minutes?
     
  8. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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    Because the three timed periods are binary divisable, you could use a 15 minute 555 astable (or 7.5 minute etc), and a binary counter IC.

    Even simpler might be to use a 555 and a decade counter like a 4017, with the 3 outputs on pin 2, 4 and 8 for *2, *4 and *8 timing with a 7.5 minute 555 astable.
     
  9. tracecom

    AAC Fanatic!

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    How does one use a button to allow the beeper to sound at 60 minutes, but not at 30 or 15?
     
  10. Katherine1

    Thread Starter New Member

    Mar 1, 2013
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    Actually, I want to test on this circuit for a month trial. This circuit will act as a reminder to people to do a certain task after the time set had lapses. if they fail to do so, the buzzer will keep on beeping until the switch is off..

    I think i want to change my time intervals to 10, 15,20, and 30 minutes (4 buttons separately).

    One ques, I don;t really understand the concept why the beeper only sound at the last timing ( for the 60 mins above) ?
     
  11. tracecom

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    That was my question, but maybe I misunderstood your need. I thought that you wanted to select the time by choosing the corresponding button. Is that correct, or do you want the beeper to go off after 10 minutes, then again after 5 more minutes, then again after 5 more minutes, and then again after 10 more minutes?
     
  12. Ritjeet

    New Member

    Mar 6, 2013
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    Can 555 timer be used for generating a 13.5 V 140 Hz pulsating DC generation where current can be varied between 0-2 amps? please help.
     
  13. Katherine1

    Thread Starter New Member

    Mar 1, 2013
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    yaya..i want to choose the time I want tru the buttons.
     
  14. MrChips

    Moderator

    Oct 2, 2009
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    I would start off with a 555 timer running at say around 1Hz (I have not done the math as yet). I would feed this into a multi-stage binary counter to produce 5-min period signal, followed by more binary counters (or combine this with the first set of counters).

    Then I would use the push buttons to set one of four flip-flops which will be used to select one of the four desired times. The output of this multiplexer can be used to trigger a beeper circuit.
     
  15. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    I believe the simplest ckt. was suggested by tracecom, use 4 555's as one-shots & OR the outputs to drive buzzer. At power-up buzzer will sound untill a time is selected, then be quiet untill one 555 times out & resets, starting buzzer. Could use C version of 555 to reduce power drain Accuracy will not be a problem if there are not wild swings in environmental temperature.
     
  16. THE_RB

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    The same way you would have to do it on a 555. I imagine you would use a 3 position switch to set the desired time, then a button to start the timing process.
     
  17. tracecom

    AAC Fanatic!

    Apr 16, 2010
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    OK, but the OP didn't want a switch; she wanted 3 different pushbuttons, each of which would be for a different delay time. That's what caused me to suggest three 555 circuits instead of one.
     
  18. Katherine1

    Thread Starter New Member

    Mar 1, 2013
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    i think i can understand, is it use 3 555 timers in 1 circuit, which each 555 timer have the diff time setting?
     
  19. Katherine1

    Thread Starter New Member

    Mar 1, 2013
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  20. tracecom

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    C1 is a noise suppression capacitor that actually plays no role in the timing. R1 is a pullup resistor to hold the reset pin and the trigger pin high until SW1 is pushed. The timing is controlled by C2 and the choice of R2, R3, R4, or R5.

    In operation, the user operates a switch to select either R2, R3, R4, or R5 depending upon how long a delay desired, and then presses SW1 to start the timer. If you would be satisfied with that operation, then this would be a solution for you. I will be happy to calcutate the appropriate values for the resistors and capacitor if you want to use this.

    If you must have a separate pushbutton for each of the times you want, then I think that a separate 555 circuit for each time is the simplest choice. That would mean four similar 555 circuits, one for each of the four times you want. If that is what you want, I will draw a diagram and post it.

    Just say which solution you want and the times. Don't forget that the times won't be exact because of the tolerance in components and the effects of temperature and aging.
     
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