Flashing LED used to switch transistor?

Discussion in 'The Projects Forum' started by JBMetal, Jun 10, 2011.

  1. JBMetal

    Thread Starter New Member

    Jun 10, 2011
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    0
    Hi

    I am trying to come up with a very small, low part count circuit to cycle a miniature vibrating motor on and off. Is there any way that a flashing LED (multivibrator astable?) can be used to switch a transistor? Otherwise maybe a phototransistor/flashing led pair maybe?
    Suggestions are much appreciated. :)
     
    Last edited: Jun 10, 2011
  2. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    That's an interesting idea, actually. Hadn't ever thought to try it.

    Some flashing LEDs have built-in current limiting along with the flash circuitry; if so that means you wouldn't need a base current limiting resistor, as the LED itself would limit the current to somewhere between 15mA and 25mA (usually), and would probably work over a range of voltages (say, 3v-10v, depending on the particular flashing LED; see the specifications for the particular LED in question). If it had a narrow range of voltages, you would need to use a current limiting resistor in series with it for the power supply that you were planning on using.

    You can use a single flashing LED to flash a whole string of LEDs, and also use it to limit the current. No reason you couldn't use it to drive a transistors' base as well.

    You may need to add a base return resistor; that is a resistor connected from the base to the emitter which ensures that the transistor can turn fully OFF. A 220 Ohm to 330 Ohm resistor would likely be sufficient.
     
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