HELP with 555 timer

Discussion in 'General Electronics Chat' started by itel933, Aug 26, 2010.

  1. itel933

    Thread Starter Member

    Aug 26, 2010
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    Does anyone have a schematic for a count down timer (5-10 mins) using a 555 chip?

    If the timer is activated by a push button switch, is it possible to make it so that when I push the button it will keep the timer going even after the button is released?
     
  2. bertus

    Administrator

    Apr 5, 2008
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  3. itel933

    Thread Starter Member

    Aug 26, 2010
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    What I am looking to make is a count down timer, where when I press a button, the circuit will let me know when the time has expired. I would like to be notified either by a flashing led, buzzer or both
     
  4. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    Take a look at this thread:
    2 led timed circuit

    In that thread the OP wants to make a kitchen timer.
    Bill_Marsden also provided the circuits in that thread.

    Bertus
     
  5. itel933

    Thread Starter Member

    Aug 26, 2010
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    can a piezo buzzer be used in place of the sonalert? if I integrate this into a circuit that I have and a push button has a fuction already. Can I use that same button to silence the alarm? If I only needed one LED how do I make the changes to the plan?
     
  6. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    You just did a hijack on the other thread.
    We like to keep the question and answer in one thread.
    This is your own thread.
    I moved your post over here.
    You are refering to this post:
    http://forum.allaboutcircuits.com/showpost.php?p=269134&postcount=10

    You can remove one of the leds.
    The sonalert is a kind of buzzer with buildin oscillator.
    If the piezobuzzer has a buildin oscillator it will work too.

    Bertus
     
  7. Wendy

    Moderator

    Mar 24, 2008
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    What part of the world are you? It has some bearing as to where to get parts. You'll note the old hands have it as part of their profile.
     
  8. itel933

    Thread Starter Member

    Aug 26, 2010
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    Im in New York. I tried your timer using the 555. I dont want to attach the sonalert so I stopped after I installed the 1k resistor on the right side of the shematic. I only have one switch.

    when I plug the battery in the red led comes on with the switch pressed. after 3 mins (I have 165k resitor) nothing happens. when I touched the battery it was hot. what am I doing wrong? Do I have to complete it with everything installed in order for it to work?

    Alex
     
  9. Wendy

    Moderator

    Mar 24, 2008
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    Did you follow the plans on the protoboard for the 555 Monostable. For the moment leave the buzzer off.
     
  10. itel933

    Thread Starter Member

    Aug 26, 2010
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    i followed the plan. i put a 1000uf cap instead of a 10uf
    i also used a 15 k resistor fot the "rt". i followed the values for the kitchen timer project . im burning the 10k resistor. what seems to be the problem. can i burn out the timer if i keep trying.
     
  11. tom66

    Senior Member

    May 9, 2009
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    Hmm, feel the 555 timer, is it hot? Even if it is slightly warm, it usually means the timer is a dud. What are you building it on, breadboard? Stripboard? If you have a short on the output, the timer could be damaged, this could lead to the hot battery you noticed.
     
  12. itel933

    Thread Starter Member

    Aug 26, 2010
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    Bill

    I took everything apart and built it again. the 10k resistor on the "A" side of the capacitor is smoking when i apply power to the curcuit. I'm using a switch from "GND" to "trigger" and i also configured where i use a switch connecting "GND" to the "A" side of the capacitor. both with the same results.

    when I plug power in the red LED turns on, when I press the switch the green LED comes on then after a few seconds i smell the resistor burning.
     
  13. Wendy

    Moderator

    Mar 24, 2008
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    OK, are you using the 555 Monostable page as is, with a 9V battery?

    Something sounds very wrong. Using 15VDC, the maximum voltage a standard 555 can take, a 15KΩ resistor will only draw 1.5ma, and dissipate 22.5mw (it will be barely warm). My conclusion is your using something much more than 15VDC.

    I can connect a 15KΩ directly across the power supply voltage with no affect. To begin to heat it up would take at least 61 Volts.

    We need more information as to what you are doing.

    BTW, are you sure you're aren't using a 1.5KΩ resistor? <brown><green><red>

    A 15KΩ is <brown><green><orange>.

    A 1.5KΩ would be noticeably warm, but not hot using 15VDC.
     
    Last edited: Aug 30, 2010
  14. itel933

    Thread Starter Member

    Aug 26, 2010
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    Im using a 9 volt batt. Im using a 556 because I want to use this in con juction with something else. (i know a 556 is 2 555 in one) Im only testing the timer by itslelf. i havent even begun to build the second part of my project. Im going to triple check the values of all the resistors.
     
  15. tom66

    Senior Member

    May 9, 2009
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    Make sure you have the correct pin out for the 556. It isn't the same as two 555s stuck one on another; there are shared power pins, for example. Also, make sure you're not using the 558, which manages to fit 4 x 555s in one chip, but has to combine some lines into timing and only has one reset/control voltage IIRC.
     
  16. Wendy

    Moderator

    Mar 24, 2008
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    Thing is, there is no way the resistor (if it is a 15KΩ) will have any noticeable temperature. This is fundamental physics, ergo, the resistor isn't 15KΩ. ¼W of dissipation will require a minimum of 324Ω at 9VDC. I'm betting your resistor is 150Ω <brown><green><brown>.

    A 556 will work, but as Tom66 said, the pin outs are radically different.

    Do you have a DVM (Digital Volt Meter)?

    Here is a simple conversion worksheet I came up with a while back.

    http://forum.allaboutcircuits.com/picture.php?albumid=41&pictureid=308

    As was mentioned, if the chip has gotten hot, it is probably burned out.
     
    Last edited: Aug 30, 2010
  17. itel933

    Thread Starter Member

    Aug 26, 2010
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    yes i have a volt meter. im using the "#5 pin" on the 556 as the out. Im using a Radio shack 556cn (part # 276-1728.

    the original plan called for a 10 k resitor. Im now using a 15k as per your instructions, Bill

    No more burning, but it smells like something is burning and the cap is getting hot (C1)

    How are the lights supposed to "flash", if at all. I plug in the 9v batt and red LED is lit. I press the switch Red goes out green turns on.
     
  18. Wendy

    Moderator

    Mar 24, 2008
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    Are you using the same 556 chip? We've covered that, it is probably blown if it got hot. Since you're not using my plans (a 556 is a different part) you'll need to have a new schematic. One was in the link I provided, but you also need to ground some of the other 556 pins.

    If you are using a schematic may we see it?

    We'll help where we can. Sometimes minor changes aren't so minor. :)

    If C1 is getting hot you have probably connected it backwards to the power supply. Electrolytic capacitors, like batteries, are polarity sensitive. If it is bulging on the top it has gone south, so keep your eyes open.
     
  19. RRITESH KAKKAR

    Senior Member

    Jun 29, 2010
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    pls tell what Is the maximum Freq. of 555 Ic........!
     
  20. Wendy

    Moderator

    Mar 24, 2008
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    Depends on the exact make and model. The conventional 555 is around 1Mhz, while the TI CMOS version (TLC555) is around 2 Mhz.

    If you want to persue this you need to start your own thread. Hijacking someone elses thread is strongly discouraged here.
     
    RRITESH KAKKAR likes this.
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