Connect with us

Will a 555 timer switch on and off, on and off, etc?

Discussion in 'General Electronics Discussion' started by pityocamptes, Sep 25, 2012.

  1. pityocamptes

    pityocamptes

    79
    0
    Jul 26, 2012
    I have a small air pump that needs to cycle, the pump draws very little current and voltage ~3.5 volts. Its a mini pump. The specs say 7 seconds on and 7 seconds off for duty cycle. Will a 555 timer circuit do this? 7 secs on and 7 off, 7 on and 7 off, etc until the unit is powered off via a control switch? Anyone have a schematic that I can reference? Thanks!
     
  2. wingnut

    wingnut

    233
    8
    Aug 9, 2012
  3. pityocamptes

    pityocamptes

    79
    0
    Jul 26, 2012
  4. CocaCola

    CocaCola

    3,635
    4
    Apr 7, 2012
    This will get you close...

    [​IMG]
     

    Attached Files:

    • 77.jpg
      77.jpg
      File size:
      79.6 KB
      Views:
      505
  5. pityocamptes

    pityocamptes

    79
    0
    Jul 26, 2012
  6. pityocamptes

    pityocamptes

    79
    0
    Jul 26, 2012
    Hey were did you get that calculator? I may need to play around with the time frames a little. Thanks!
     
  7. CocaCola

    CocaCola

    3,635
    4
    Apr 7, 2012
  8. pityocamptes

    pityocamptes

    79
    0
    Jul 26, 2012
    Do you have a list of 555's with different voltage levels? I didn't realize that made different ones. I probably need a low voltage input 555 that has an output of at least 150ma. Thanks!
     
  9. CocaCola

    CocaCola

    3,635
    4
    Apr 7, 2012
    Go to a supplier like digikey or mouser and start looking at the specs... If you need a higher drive current you can add a transistor... Also don't forget to add a flyback diode across the pump... Google transistor as switch and flyback diode for more info...
     
  10. pityocamptes

    pityocamptes

    79
    0
    Jul 26, 2012
    Thanks. You wouldn't happen to have a schematic that uses a transistor switch in the 555 timer circuit, so that I can get a visual idea? Thanks again!
     
  11. CocaCola

    CocaCola

    3,635
    4
    Apr 7, 2012
    I could but you have already been given the path to solving this, time for you to do a little of your own legwork...

    or read the entire document wingnut linked you to...
     
  12. pityocamptes

    pityocamptes

    79
    0
    Jul 26, 2012
  13. pityocamptes

    pityocamptes

    79
    0
    Jul 26, 2012
    Here is a schematic using switches and diodes, I added the diodes, "M" is the motor of the pump, did I do the diodes right? Does the schematic look right? Thanks!

    [​IMG]
     
  14. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,174
    2,689
    Jan 21, 2010
    The diode in series with the motor is not required.

    The other diode is in the incorrect place. It should be across the motor.

    3V may be insufficient to power the 555.

    You may have to decouple the 555's power from the motor

    The motor (with these modifications) will see just under 3V.

    What is R4 for? It's not needed, remove it.
     
  15. pityocamptes

    pityocamptes

    79
    0
    Jul 26, 2012
    Thanks. How does this look?


    [​IMG]
     
  16. CocaCola

    CocaCola

    3,635
    4
    Apr 7, 2012
    I believe you have addressed most issues from a quick look over, just make sure the 555 you get will operate at 3V and also as Steve touched upon the motor might make a bit too much noise for the 555 to be happy... Make sure that C2 is as close to pin 8 as possible, you can bridge directly from pin 8 to pin 1 of the 555 with C2 making the distance minimal... You might also need a few other value caps to help with the noise as well but that will have to be determined at that time if you have issues...
     
  17. pityocamptes

    pityocamptes

    79
    0
    Jul 26, 2012
    How will I know if I have noise? Will the "noise" provide a false trigger? If I do get noise, where do I place the caps? For my programmed time I was going to use:

    R1 = 600k
    R2 = 500k
    C = 20uf

    I may change them slightly, but this is what I was looking at... thoughts? Thanks!
     
  18. pityocamptes

    pityocamptes

    79
    0
    Jul 26, 2012
    Oh, also is the schottky diode, 1n5817 facing the correct way?
     
  19. CocaCola

    CocaCola

    3,635
    4
    Apr 7, 2012
    Yes, the diode is shown correct...
     
  20. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,174
    2,689
    Jan 21, 2010
    Weird stuff will happen.

    It's hard to be more specific, but yeah, look out for odd things when the motor is running and also when it switches off.
     
Ask a Question
Want to reply to this thread or ask your own question?
You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.
Electronics Point Logo
Continue to site
Quote of the day

-