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Will this 555 circuit for 8 leds flashing work? Answered

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Will this 555 timer work and make these 8 leds flash with this circuit I drew up.

4 Replies

Eärendil_the_mariner (author)2013-01-18

A couple more notes:
Those LEDs are rated at only 30 mA continuous, whereas this circuit runs them at around 50 mA. Not a problem for a low duty cycle with short pulses, but this circuit as you intend has a high duty cycle. Where you might run into a problem is that you're right at the maximum capacity of the output pin (200 mA). You might want to have the output pin drive a transistor to source the LED current.

With the resistors you've selected, the LEDs will be on about half the time, and flashing a bit over once per second. This is why Rick recommends something more like a 1MOhm resistor, to slow the pulse rate down. What I would recommend is that you replace the 470 KOhm with a 1 MOhm and then put a diode across it. This allows the cap to charge only through the 1K resistor, resulting in a very quick flash, followed by a relatively longer off period as the capacitor is forced to discharge through the 1M resistor. You should, of course, play around with the resistor values until you find a flash that is what you want,

Good luck!

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rickharrisBest Answer (author)2013-01-16

output for the 555 is pin 3 not pin 2

Capacitor should go to ground.

5 should have a small cap to ground.

didn't check the value but the 1 K looks small I might expect something closer to 1 Meg ohm and 47 K rather then 1 K and 470K

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mykiscool (author)rickharris2013-01-16

Ok, thanks I'll fix those changes. Like they always say, measure twice cut once. Glad I didn't go ahead before verifying and ruin my 555/led.

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