Newbie 555 timer understading

Discussion in 'General Electronics Chat' started by Jemin Patel, Feb 26, 2015.

  1. Jemin Patel

    Thread Starter New Member

    Feb 26, 2015
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    Hey everyone,
    I am a newbie to electronics and I have seen a lot of schematics where people use 555 timer to drive bunch of leds. Why use 555 when the leds can be driven without it. Thanks in advance.

    J
     
  2. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    You use the 555 if you want to flash or time them. If they are to be on steady, then all you need is a DC supply and a resistor.
     
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  3. Jemin Patel

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    Feb 26, 2015
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    Thank you MikeML for you quick reply.
     
  4. Dodgydave

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    Jun 22, 2012
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    you can dim them using a 555 timer using Pwm.
     
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  5. ErnieM

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    Apr 24, 2011
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    I've even seen the 555 used not to flash the LEDs or control brightness, but as a simple on/off switch in a night light.

    It used the comparator section to read a light sensor and only turn the LED on in a dark room.

    The 555 is quite a useful device with an incredible potential for many many uses.
     
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  6. Jemin Patel

    Thread Starter New Member

    Feb 26, 2015
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    Dodgydave,
    Thanks for the reply. I guess what I was asking is that a variable resistor can dim the leds too so why go with a 555? You still need to use a variable resistor to dim even though you'd be using 555, right? Is using 555 for PWM more effecient?
     
  7. Jemin Patel

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    Feb 26, 2015
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    Hi ErnieM,
    Thanks for you reply as well. I am sorry if I sound like I am against using 555. I really am not. I am just trying to understand its implementation when it comes to simple circuits.

    Thanks
     
  8. Dodgydave

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    Jun 22, 2012
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    yes, pwm is more efficient and creates less heat.
     
  9. Wendy

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  10. Jemin Patel

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    Feb 26, 2015
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    Super. I appreciate your help! And thank you for the article. I just joined the site yesterday and I did a search on 555 and thats the first article I ended up reading. Thank again!
     
  11. Jemin Patel

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    Feb 26, 2015
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    Thanks Ernie.
     
  12. MikeML

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    Using PWM to dim a 20mA LED is stupid, however...
     
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  13. ErnieM

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    Apr 24, 2011
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    That would depend on the application, would it not?

    I once used PWM via a micro controller to control the brightness of a single LED. We sold them for about $30 a piece to someone who used them as cockpit lighting as incandescent replacements.

    The trick was getting the brightness of a LED to mimic that of an incandescent over a 10 to 28V range. The other trick was getting the whole thing to fit into a metal barrel about the size of the eraser holder on a #2 pencil.
     
  14. MikeML

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    I have several LEDs run off the dimmer bus in my Cessna. I was able to get the LEDs to match the incandescent dimming curve using a couple of diodes, a transistor and some resistors...
     
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  15. tom_s

    Member

    Jun 27, 2014
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    anyone else here think that the 555 rivals the invention of sliced bread?

    such a versatile ic
     
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  16. crutschow

    Expert

    Mar 14, 2008
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    Only if you use an inductor in series to average the current.
    If you still use a resistor in series with the LED to limit the current then there will be little change in the efficiency for a given average LED current and supply voltage.
     
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  17. gerty

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  18. Jemin Patel

    Thread Starter New Member

    Feb 26, 2015
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    This is great man. Thanks.
     
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