Flickering Led Circuit

Discussion in 'General Electronics Chat' started by hepoul, Mar 18, 2010.

  1. hepoul

    hepoul Thread Starter New Member

    Mar 18, 2010
    Excuse me, but my english isn't good. I find in the WEB the following diagram, to make a led with flame effect (like a candle). In theory, this circuit makes the led flashing randomly. I did on protoboard, and don't work, the LED still "on" (no flashing).

    I simulate on Multisim, and when run, the timer is broke. To prevent this, I connect pin 5 to ground. But the led still "on" (no flashing)

    I need make this effect.

    Can you help me? Thanks for advance.

    Attach the original file for more information.

    (Credits to owner)

    Attached Files:

    Last edited: Mar 18, 2010
  2. AlainB

    AlainB Active Member

    Apr 12, 2009
    Montréal, Canada
    Be sure to have a stable power supply from the 7805 first. As it is, I would suspect that it could oscillate.

    Here is the typical way of wiring it according to many datasheets:


    Attached Files:

    Last edited: Mar 18, 2010
  3. SgtWookie

    SgtWookie Expert

    Jul 17, 2007
    In the vast midwest of the USA; CST
    I agree with AlainB. In addition to the 0.1uF capacitor, the 555 timer requires an additional capacitor of at least 1uF in size. I suggest using a 0.1uF right at the output of the 78L05 and a 10uF across the power rails. Additionally, each IC should have a 0.1uF capacitor across its' power pins; metal poly preferred, ceramic are OK.

    These are known as bypass capacitors. They are not shown in most schematics because it makes the schematic more difficult to understand (clutter) and bypass capacitors are always required for IC's, so it is assumed that people know to add them.

    If you are using a standard transistorized 555 timer, you may need to use a 330 to 470 Ohm resistor between pin 3 and the 5v supply. This is because the output (pin 3) of the transistorized version of the 555 cannot go higher than Vcc-1.3v, which is 5v-1.3 = 3.7v. It may not be going high enough for the particular ICs that you are using to be seen as a logic 1.
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