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False triggering of a 555 timer

Discussion in 'Electronic Projects Design/Ideas/Reviews' started by jacbk6121, Mar 6, 2017.

  1. jacbk6121

    jacbk6121 Member

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  2. aardyvarky

    aardyvarky Member

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    Ok, so you want the high-tech approach, fair enough.
    How much of a problem is self-triggering on power-on?
     
  3. jacbk6121

    jacbk6121 Member

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  4. dave

    Dave New Member

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  5. aardyvarky

    aardyvarky Member

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    To get a higher output, do this:
    upload_2017-3-17_15-26-49.png
    0.4v is neither here nor there as far as the motor is concerned, and use a low dropout regulator. Remember it will need at least 1mA to work (e.g. 3K6 supplying an LED), and you will need one that can supply 500mA or 1A (so cheap might as well get a 1A).
    I still agree with others though, that this might not prevent false triggering, hence my previous idea.
     

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  6. aardyvarky

    aardyvarky Member

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  7. jacbk6121

    jacbk6121 Member

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    It's a problem, if ever I market this product it will seem odd to the user. I think this is the same problem as the man. switch starting the timer which will also seem odd. Cure one and you cure the other I hope. I have great hopes for the LDO regulator.
     
  8. jacbk6121

    jacbk6121 Member

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    One alternative is to add another magnetic switch at the top of the upper reservoir which would eliminate the 555 timer and the false triggering issues. That switch could activate a relay which will shut the pump down. This adds some cost and extra wires that may not be as attractive, but this is intended as a scientific toy so that may not be an issue. If that relay fails I do have overflow protection so that won't be an issue.
    I'll try the LDO regulator first and then decide which way to go.

    Jacques
     
  9. aardyvarky

    aardyvarky Member

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    You didn't like my ancient Greek/Chinese solution (the big water tank)?
    If you use another mag switch at the top, how will it turn the relay off?
    Could you try with a more puny pump or run it at a lower voltage? Might not drag the V down so much?
    Your manual switch looks really cheap and nasty - could you get a better quality one?
     
  10. jacbk6121

    jacbk6121 Member

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    1. I want the smallest tank possible that achieves the goal of a 1 to 2 day supply to the dipping bowl;
    2. Haven't figured the details out yet but I'm sure it can be done with a combination of NO and NC contacts on one or two relays;
    3. this is the smallest pump that will do the job;
    4. You're right, it's got the look I want but it might be nasty (spikes, noise, etc.), any suggestions?
     
  11. jacbk6121

    jacbk6121 Member

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    Just received the LDO regulator LM 2941. It's not clear to me what the on-off pin does, should it be turned on or off and how is that done?

    Can't upload the data sheet because it is too large for the server.
     
  12. jacbk6121

    jacbk6121 Member

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    Just received the LDO regulator LM 2941. It's not clear to me what the on-off pin does, should it be turned on or off and how is that done?

    Can't upload the data sheet because it is too large for the server.
    I'm guessing that the on-off pin should be set to on by grounding. But I wonder why an on-off function is provided in the first place?
     
  13. audioguru

    audioguru Well-Known Member Most Helpful Member

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    When the LM2941 is turned on then it has no voltage loss caused by an external transistor or Mosfet being used to turn on a load. The on-off input current is very low.
     
  14. aardyvarky

    aardyvarky Member

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    From the datasheet:
    upload_2017-3-22_14-50-19.png
    upload_2017-3-22_14-51-41.png
    upload_2017-3-22_14-53-12.png
    upload_2017-3-22_14-58-40.png
    Hopefully that will be enough info for you.
     
  15. aardyvarky

    aardyvarky Member

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    Have ordered pump like your one - it's quoted at 3v - 4.5v at ~150mA. I'll test it with a used battery and see what I get.
    Might be a while cos it's a Chinese special.
     
  16. jacbk6121

    jacbk6121 Member

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  17. jacbk6121

    jacbk6121 Member

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    Th
    Thanks
     
  18. jacbk6121

    jacbk6121 Member

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    So I have tried the LDO regulator and it has not helped. I could fiddle with it and maybe get it to work but I have decided to go the other route of an additional level switch which I had been avoiding all this time. It makes for a circuit with much less parts which in the end will be more reliable. I have attached the schematic, it's rather tortuous and I'm not 100% sure that it will work, proof will be in the pudding.
     

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  19. Les Jones

    Les Jones Well-Known Member

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    It will sort of work. It will maintain the level at the high level.While it is at the high level RL2 will be energised consuming current an discharging the battery. As soon as le level drops so the LS2 is open RL2 will be de energised and the pump will run until LS2 closes. The level will never drop low enough for LS1 to operate. Also RL1 will behave like an old fashioned buzzer.

    Les.
     
    Last edited: Mar 23, 2017
  20. jacbk6121

    jacbk6121 Member

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    Yup, you're right, that's what I describe for the midway level operation, pump runs. That's OK when it's filling but not when it's draining. When the water reaches the high level I want the pump to start only when it reaches the low level.
     
  21. jacbk6121

    jacbk6121 Member

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    Somehow there needs to be two modes of operation. In the fill mode the pump runs when LS1 is on or off and stops when LS2 is on. In the drainage mode the pump needs to be off regardless of the position of LS2 and start only when LS1 is ON.
     

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