This circuit will flash the led on and of at regular intervals.
How it works:
From left to right, the two resistors and the capacitor set the time it takes to turn the led on or off, by changing the time it takes to charge the capacitor to trigger the timer. Next is the 555 timer, this is where all the work gets done to determine the time the led stays on and off. It contains a complicated circuit inside, but since it is packaged in the IC it can be used as a simple component.
The two capacitors that are right of the timer are just accessories so to speak, but are needed for the timer to work correctly. The last part is the resistor and the led, the resistor is there to limit the current on the led so that it won't burn.
(click to enlarge)
(click to enlarge)(pin numbers on actual IC)
6 comments:
thank you very much!
Using a 1 kOhm resistor as R2, I could only get a steady light. Increasing the value of R2 leads (eventually) to blinking, with higher resistance values corresponding to longer blinks, as you would expect from a RC-driven system. I'd recommend using a 100 kOhm potentiometer in place of R2.
No and yes, with the 1k ohm resistor you get flashing, but the flash is so fast that the eye can't see the individual on/offs, you end up seeing a dimmed steady light..
The 100k ohm variable resistor is a good solution to control the blinking rate.
Please note that the values used are not for any specific blinking rate, they are reference only used for a "generic" led flasher (which it is what this does, only at a very fast rate).
I encourage you to experiment on the values to see what works and use the description to figure out Why it works that way.
I'm looking to build an LED flasher that will blink at 100 beats/minute for a Cardio-Pulmonary Resuscitation (CPR) demonstration. Is there a place in this circuit that would accept a potentiometer or a way to calculate the required resistance? Thanks
R1=100, R2 = 300 k and C1 = 5 uF gives a rate of about 0.5 Hz. Then just adjust either or both to change rate.
Nice
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