Blinking led question

kahless78 · Post by **kahless78** » Thu Apr 01, 2010 12:29 am

I see that you can get blinking leds. Now can I just wire them up to my power source and they will blink? Or do I have to get additional parts to make them blink?

USS Atlantis · Post by **USS Atlantis** » Thu Apr 01, 2010 5:26 am

The ones advertised as "Blinking" contain a micro-circuit in them to cause the blinking effect

No need for additional parts - except AS ALWAYS, a resistor - use the same calcs for the blinky's as for standards

One note - blinky LEDs have notoriously had a much shorter life than standards - something about how they blink

This is not true with standard LED's that have a blinky circuit to drive them

Mr. Engineer · Post by **Mr. Engineer** » Fri Apr 02, 2010 6:23 am

Yep, you have to use a resistor just like any other LEDs. You don't want it to go blink.. blink.. pop...

CanabisRex · Post by **CanabisRex** » Fri Apr 02, 2010 2:41 pm

well, here's an amended question for the same subject..how do you set up a blinking circuit?

USS Atlantis · Post by **USS Atlantis** » Fri Apr 02, 2010 3:03 pm

CanabisRex wrote:well, here's an amended question for the same subject..how do you set up a blinking circuit?

Simplist

Capacitor and two resistors feeding into a 555 timer

This schematic yields This blinking

By varying the values of R4, R5 and C2 you can vary the pattern

The Diode (D1) is in there to give a less than 50% duty cycle - normally, with 555 timer circuits, your LED has to be ON at least 50% of the time

By putting the diode in parallel with R5, you invert the duty cycle making it less than 50%

tetsujin · Post by **tetsujin** » Fri Apr 02, 2010 6:33 pm

USS Atlantis wrote: The Diode (D1) is in there to give a less than 50% duty cycle - normally, with 555 timer circuits, your LED has to be ON at least 50% of the time

By putting the diode in parallel with R5, you invert the duty cycle making it less than 50%

Alternately, you could just hook the other end of the diode to the 555 output - make the 555 "sink" current rather than "drive" current...

So set up the 555 for an 85% duty cycle, but hook the LED cathode to the output instead of the LED anode, and then you've effectively got a 15% duty cycle.