low voltage 555 with flashing led

Discussion in 'The Projects Forum' started by asingla, Nov 14, 2009.

  1. asingla

    Thread Starter New Member

    Nov 14, 2009
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    I am very new, can read circuits more or less.
    I have an application that I am having trouble with and was hoping someone could help.
    I essentially am using a low voltage 555 times with a 1.5v source. I am trying to get an LED to flash on for 25 seconds and then off for seconds. I am having a bear of a time with this. Ultimately, I would like to know how to calculate for different on off cycles. I downloaded a program called 555timer but the lowest input voltage it allows is 4.5v so I cannot get this to work.
    I have no choice but to use 1.5v, so if this is not possible with the low voltage 555, I would appreciate some help in finding the right direction.

    Thanks to all and any in advance!
     
  2. Wendy

    Moderator

    Mar 24, 2008
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    A CMOS 555 is speced at 2V minimum. You might get it to work at 1½V, but it won't be that reliable. The part numbers to look for is TLC555 (Radio Shack) or 7555. There are other makes out there.

    What is your application?

    Have you read these?

    The 555 Projects

    Bill's Index
     
  3. asingla

    Thread Starter New Member

    Nov 14, 2009
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    I am using the TLC555 from the shack. I am using it to power on a miniature motor that runs in the 0.9v-1.5v range
     
  4. Wendy

    Moderator

    Mar 24, 2008
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    Two things wrong with that, the first has been discussed, not enough voltage. You really need two batteries for 3V.

    The second is CMOS chips have an odd characteristic, and that is the lower the voltage the less current they'll put out. At 1½V it should be around 1ma (0.001A). You can't light a LED well with that.

    Check my articles on the the long term flashers, they cover that.

    You could turn on a transistor and drive the motor, but you still need more voltage.

    How about using a 3V coin cell? You could have a 1½V battery for the transistor and motor.

    Another possibility, the CR123 battery. It is about the size of a AA, but has 3V and pretty good current.
     
  5. asingla

    Thread Starter New Member

    Nov 14, 2009
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    a 3v button cell is a great idea!
    any pointers on a circuit to use?
     
  6. Wendy

    Moderator

    Mar 24, 2008
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    Have you read my projects? They are nothing but ideas. They can also show you how to use transistors for a chip that is so weak at that voltage.
     
  7. haha11

    New Member

    Dec 10, 2008
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  8. Wendy

    Moderator

    Mar 24, 2008
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    Yep, but how does that help? If it put out a steady voltage for the 555 maybe, but it also has to power the LED.

    Maybe it is possible to use a starved 555 circuit at 1½V and power a joule thief LED. Wouldn't be that reliable, but it would work for a little while. Ever since LEDs started using more voltage it is a little harder to do this stuff, though some interesting ideas have emerged.
     
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