Project: Stroboscopic LED light

Discussion in 'The Completed Projects Collection' started by cumesoftware, Jun 6, 2007.

  1. cumesoftware

    Thread Starter Senior Member

    Apr 27, 2007
    This is a stroboscopic light that uses LEDs and has the advantage of being battery powered. You can regulate the pulse from 0.1 seconds up to 1 second.

    Components list:
    B1-4 - 1.2V (Ni-CD or Ni-MH) or 1.5V (carbon-zinc or alkaline) battery;
    C1 - 1.0uF tantalum capacitor;
    C2 - 10nF ceramic capacitor;
    D1 - 1N4001 rectifier diode;
    D2-13 - Nichia NSPW510CS LED;
    IC - 555 timer (LM555, NE555 or equiv.);
    R1 - 120K carbon resistor (5% tol., 1/8W);
    R2 - 1M variable resistor (10% tol., 1/8W);
    R3 - 12K carbon resistor (5% tol., 1/8W);
    R4 - 82Ohm carbon resistor (5% tol., 1W);
    R5 - 1Ohm wirewound resistor (5% tol., 3W);
    T - TIP32 PNP bipolar transistor.

    - The rectifier diode D1 and the switch S2 seem to have no pursose, but they have (yesterday I thought it too, but then I remembered their purposes). D1 serves here as a zener diode, causing a voltage drop when S2 is switched off. I did this because rechargeable batteries (Ni-CD or Ni-MH) have lower voltages than the non rechargeable ones. Since we are talking about white LEDs that have a relatively high voltage drop, and thus their brightness can vary greatly with respect to changes of the supply voltage, then this solution is more adequate. I just calculated R5 considering the use of rechargeable batteries, and D1 serves when normal batteries are used (actually I used that kind of arrangment in another project and I will post it in another post, just for reference).
    - R2 is used to regulate the pulse. For R2 you could use a potentiometer instead. In some places potenciometers are easier to find than variable resistors. When using a potentiometer tie one of the end legs to the cursor leg (just for reliability), and you will have a variable resistor).
  2. cumesoftware

    Thread Starter Senior Member

    Apr 27, 2007
    Here is another project where rectifier diodes are used to cause a voltage drop. This is a LED flashlight. You can see that S1 and D1 serve the same purpose, being S1 swiched on only if rechargeable batteries are used. I could use a resistor instead of a diode, but as you see, the load can change, so the voltage drop across a resistor would change either. Just for reference, D2 and D3 are used for focused and intense ilumination and D4 is used for a more difuse ilumination (reading books, where the angle needs to be wider). They can be used in conjunction as well.
  3. markosillypig

    AAC Fanatic!

    Jul 21, 2008
    hi is there an alternative to the tip32 used for the
    Project: Stroboscopic LED light
    and if there is not do i use a tip32b
    or a tip32c any preference

  4. bertus


    Apr 5, 2008

    Depending on the current you want to switch, you can use a BD138,(BD138,BD140) or a BD246.
    See datasheets.

  5. cumesoftware

    Thread Starter Senior Member

    Apr 27, 2007
    There are no differences between the TIP32, and the other versions TIP32A/B/C besides the maximum emitter-collector voltage. All of them can handle up to 3A continuous. I don't recall the actual current biasing this transistor, but I will figure it out soon and give you an answer.
  6. cumesoftware

    Thread Starter Senior Member

    Apr 27, 2007
    Well, I've finally figured the value of the current biasing the transistor. It is around 1.2A.