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15465Re: Point me into the right direction please.

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  • rtstofer
    Feb 1, 2005
      --- In Electronics_101@yahoogroups.com, "Roy J. Tellason"
      <rtellason@b...> wrote:
      > On Tuesday 01 February 2005 02:31 am, rtstofer wrote:
      >
      > > Take your LED flasher example. You can look for 555 timer
      circuits
      > > on the internet. A single 555 will make one LED flash. What
      should
      > > the second do? Turn on when the first turns off? Well, any
      single
      > > transistor inverter will do that. Voila' Two flashing LEDs.
      >
      > Even that's making things too complicated...
      >
      > > Start simple, get one LED to flash using the 555. Then, get a
      > > 2N2222 transistor or most any NPN device. Connect the emitter to
      > > ground, connect a 1K ohm resistor between your power supply and
      the
      > > anode of the LED (the long lead) and connect the cathode of the
      LED
      > > (the lead near the flatted edge) to the collector lead of the
      > > transistor. Now, connect a 1K resistor between the output of the
      > > 555 and the base of the 2N2222. That's it. A simple inverter.
      > > Assuming you have a 5V power supply the LED will light up. It
      won't
      > > be very bright because the 1K resistor in series with the LED is
      too
      > > large. But, it will work.
      >
      > Nah. If you wire up one LED and resistor so that it's on when the
      output of
      > the 555 is grounded, then wire up another one so that it's on
      when the
      > output is high, you don't need the transistor inverter!

      I knew somebody would come back with that. And, of course, it is
      true because of the active pull-up of the 555. It won't work for
      every device but it will work for the 555.

      The thing is, building the inverter is worth the effort.
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