555 timer

Discussion in 'The Projects Forum' started by umer0314, Jul 29, 2009.

  1. umer0314

    Thread Starter Member

    Jul 29, 2009
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    I am working on a 555 timer project and I really need help with it. The objective to my project is to design a 555 timer on multisim that can do the following tasks:

    First task is to give a output voltage pulse for 20 seconds from the beginning,
    Second is to give a output voltage pulse once every 60 seconds after the 20 seconds are done in the first task.

    I am not sure if it needs two 555 timers and which resistors and capacitors I should use and how would I do the switching if it needs one between the two task and how would I trigger the controller, for example a push button or something else.

    Thank you
     
  2. Wendy

    Moderator

    Mar 24, 2008
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  3. umer0314

    Thread Starter Member

    Jul 29, 2009
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    No I haven't but I will now

    Thank you
     
  4. umer0314

    Thread Starter Member

    Jul 29, 2009
    29
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    I read those and I am still having difficulties starting my project. Can someone help me please?
     
  5. SgtWookie

    Expert

    Jul 17, 2007
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    OK, so...
    At power on, you want the output to be high for 20 seconds.
    Then you want the output to be low for 60 seconds.

    Do you want the next high output pulse to also be 20 seconds long, followed by 60 seconds of low output?
     
  6. umer0314

    Thread Starter Member

    Jul 29, 2009
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    when power is on the output is on for 20 seconds like 1 pulse per second for 20 seconds then after that it should be 1 pulse every 60 seconds and it should remain 1 pulse every 60 seconds until power is turned off. 1 pulse then delay for 59 seconds it should remain that way until power turned off. It should produce 3 to 5 volts.

    Thank you
     
  7. umer0314

    Thread Starter Member

    Jul 29, 2009
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    can someone help me with this please?
     
  8. jj_alukkas

    Well-Known Member

    Jan 8, 2009
    751
    5
    You need 2 555's or a single 556 to do this.

    Configure the first 555 in monostable mode and the second in Astable mode.
    The first 555 will need Ra= 2M and C=10uF 16V
    Wire Pin 3 of the first 555 to the The second's GND.Vcc will be same for both.
    The second 555 will need Ra=1.8M, Rb=15k and C=47uF
    Ouput will be available between Pin 3 and Gnd of 2nd 555.

    If you cant draw the circuit, search for 555 circuits and you will get astable and monostable mode circuits. Replace Ra,Rb and C with the above.
    This will also help in designing http://clarkson-uk.com/555-timer/program.html

    If you still can't manage, draw a diagram and post it. We will correct it.
     
  9. umer0314

    Thread Starter Member

    Jul 29, 2009
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    I am not sure If I designed this right, can you please correct it for me?

    Thank you!
     
  10. Wendy

    Moderator

    Mar 24, 2008
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    You have a major wiring error on the first 555. Pin 7 (which switches hard to ground) and pin 2 are swapped.
     
  11. jj_alukkas

    Well-Known Member

    Jan 8, 2009
    751
    5
    I couldn't understand if a few points were connected or not in the one you posted, you have provided no ground between the 2 caps of first 555, so i have drawn one myself. And if you need a trigger switch rather than an ON/Off one, add it between Pin 2 and GND of the First 555

    [​IMG]
     
    Last edited: Aug 19, 2009
  12. umer0314

    Thread Starter Member

    Jul 29, 2009
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    I designed the circuit on multisim the one you gave me can you please check If I did it right. And one more thing which 555 timer I should use there are more than one on it. For example 555 virtural, 555 timer rated, LM555CM, and others. And when I type 0.01uf capacitor it gives me 10nf capacitor. Is 0.01uf = 10nf. And by doing this circuit it should give me 20 pulses in 20 seconds then 1 pulse every 60 seconds after that. And produce 3 to 5 volts.
     
  13. jj_alukkas

    Well-Known Member

    Jan 8, 2009
    751
    5
    Basically there are only two types of 555's - The ordinary 555 which is addressed as LM555 or NE555 and the CMOS type which is denoted as 7555. The one reffered here is the normal one. LM555 is the best option, or virtual will also do. You may use the other types, but the calculations needs to be changed.

    And for the capacitor, 0.01uF = 10 x 10^-9F => 10nF ... It will be denoted by 103 when you buy it from your dealer.

    Did you really mean by 1 pulse/sec for the first 20 secs?

    This ckt waits for 20 secs from power on and then after this 20 secs gives a pulse every 60secs. You didnt specify 1pulse/sec for 20s in your first post. If that is what you want, either switch to a CD4069B or use one more 555.

    Your ckt is correct, but sorry, I made a mistake, the final output comes between Out and Vcc not Out and Gnd.

    If you made this ckt in multisim, why didnt you try simulating it??
     
  14. umer0314

    Thread Starter Member

    Jul 29, 2009
    29
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    I used the LM555CM timer. I am kind of getting confused now. I tried simulating this on multisim but it doesnt work, it just gives me a straight line. All I wont from this circuit it to produce between 3 to 5 volts. For the first 20 seconds it gives 3 to 5 volts, 1 pulse per second or not it doesnt really matter. And after those 20 seconds it gives 3 to 5 volts but 1 pulse every 60 seconds. I checked the output on a oscilloscope its just giving a straight line I dont see any pulses. I attached the circuit can you please check it for me again and if there are any errors can you please correct it for me. Or If I can design this circuit on some different software that you know about that would be helpful. I really appreciate you guys helping me but I just cant figure it out!
     
  15. umer0314

    Thread Starter Member

    Jul 29, 2009
    29
    0
    this is the circuit
     
  16. Wendy

    Moderator

    Mar 24, 2008
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    Pin 2 is connected to ground. This means the output of the first 555 is going to have a continous set signal internally. Not good, an oscillation killer.

    [​IMG]

    I have not been following this thread very closely, but that is an unusual configuration you are trying to use for the 555.

    Are you trying to do this one?

    [​IMG]

    Source: http://www.allaboutcircuits.com/vol_6/chpt_6/8.html

    Looking at the datasheets, and near as I can tell, the LM555CM is a surface mount style package. Other than that it is a conventional LM555. There are several CMOS versions, which are quite different but can be drop in replacements with adjustments, the TI version TLC555 which Radio Shack sells, and several variations of 7555.
     
    Last edited: Aug 20, 2009
  17. jj_alukkas

    Well-Known Member

    Jan 8, 2009
    751
    5
    Simulating the circuit might be causing problems, but I have built the same ckt with 2 555's but with different timings. It is used in my car alarm and it worked even till today. I can guarantee you that with the ckt I gave you will work. It will give an output of 9-12v, which I use to run a 12v relay without any transistor.
     
  18. Wendy

    Moderator

    Mar 24, 2008
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    Are you saying you had pin 2 at ground? I'll breadboard it, but with the internal set at high, the flip flop won't flop. I'm pretty sure about what I'm saying here. Pin 2 is usually kept at a high level, and brought low for a short duration to create a trigger. It is effectively the set control for the set/reset flip flop, inverted.

    Again, I've never seen that configuration, and I thought the one in the AAC book (that I referred to) was odd.
     
  19. Wendy

    Moderator

    Mar 24, 2008
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    OK, I tried this circuit...

    [​IMG]

    Over the entire range of the pot at no time did it switch. No switch, no oscillation.

    Pin 2 can not be grounded.
     
    Last edited: Aug 20, 2009
  20. jj_alukkas

    Well-Known Member

    Jan 8, 2009
    751
    5
    Oh sorry, I was offline for quite some time, it was my mistake when I drew the circuit. I pulled Pin 2 high to Vcc through a 33k and then placed a 0.1uf cap between 2 and Gnd for instant trigger at power on. Now wouldn't that work? I had designed all circuits based on it but forgot it here, my bad and sorry for the misunderstanding. Bill you are the best with 555's. The ckt triggered on power on even without the 0.1uF cap I suggested above.

    I should have taken the time to check it well. Anyway here's the modified ckt. Try a simulation.

    [​IMG]
     
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