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Old 03-18-2010, 08:23 AM
hepoul hepoul is offline
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Default Flickering Led Circuit

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.

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File Type: pdf flickering led.pdf (226.6 KB, 68 views)

Last edited by hepoul; 03-18-2010 at 08:35 AM. Reason: Add Info
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Old 03-18-2010, 11:05 AM
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AlainB AlainB is offline
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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:

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Last edited by AlainB; 03-18-2010 at 11:12 AM.
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Old 03-18-2010, 01:20 PM
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SgtWookie SgtWookie is offline
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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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