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15461Re: [Electronics_101] Re: Point me into the right direction please.

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  • Roy J. Tellason
    Feb 1, 2005
      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!
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