I Don't understand why this should work

Discussion in 'General Electronics Chat' started by jordanwb, Jul 8, 2008.

  1. jordanwb

    Thread Starter Active Member

    Jun 22, 2008
    30
    0
    I'm using schmeatics for a 555 timer from this page(at about the middle, the one labelled 555 timer tester). What I think would happen is power flows from VS to the first LED, through both resistors, then through the second LED to ground, and never change regardless of the state of the 555 timer. The reason I ask is that I bought a 555 at The Source today and it seems to be doing just that. What happens for me is that the bottom LED stays on constantly, and the top LED flashes.

    :confused:

    [Edit] I even set up the circuit on my computer in KTechLab and it doesn't work. <_<
     
    Last edited: Jul 8, 2008
  2. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    What is the exact part number that you bought?

    Some are bipolar, some are CMOS. The CMOS versions do not have much output sink/source capability. The bipolar versions can source/sink up to 200mA.

    Pin 3 is the output. It alternates between ground and Vcc/Vdd. The LEDs should flash alternately, unless you didn't hook something up properly.
     
  3. jordanwb

    Thread Starter Active Member

    Jun 22, 2008
    30
    0
    On the packaging it says "Output Current (Sink or Source) -> 200mA". Here's the product info on The Source

    [Edit #1]

    I made the circuit on another computer. I followed the schematics exactly, and it works. <_< I understand why it would work, but not why it actually works (if that makes sense).

    [Edit #2]

    I made it for real and it works. Althugh I substituted the 68K and 39K for 100K Ohm Resistors.
     
    Last edited: Jul 8, 2008
  4. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Holy cow! Did you really pay $3.99 for that timer?? :eek:

    I have a bridge that's up for sale... :D

    Seriously, you need to look at some of the major distributors.
    http://www.Mouser.com
    http://www.Digikey.com
    http://www.Newark.com

    Then there's discounters
    http://www.Jameco.com
    http://www.goldmine-elec.com
    http://www.mpja.com

    Really, you can get LOTS of those timers for what you paid. Do some shopping around. The sites I mentioned are reputable, have fair prices, and ship quickly - but you still need to be a good shopper.

    Back to your original question - well, the 555 timer has been around for many years now, and you can do a heck of a lot with it, it's dual 556 version, and even the quad 558 version (although the quad version is sort of a hassle to use, and has less output current).

    I suggest that you download datasheets for the timers from various manufacturers, such as National Semiconductor, Fairchild, Texas Instruments, ST Microelectronics, etc. - they each have their own way of describing how the IC functions, and different examples on how you can use it.

    You can learn the basics of it in a few days, and spend the next 20 years thinking up different ways to use it. Keep doing what you're doing - experiment with different configurations, etc. Be sure to read the datasheets, and understand the limitations. It's a fairly rugged IC, but you can still damage it fairly easily by using resistors of too low of a value in the wrong place.
     
  5. thingmaker3

    Retired Moderator

    May 16, 2005
    5,072
    6
    "The Source" is another name for "Radio Shack." They are a global overpricing company.
     
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