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Led 10 second light? Please help! Answered

i need help building a 2 led light that when you press the button it only stays on for 5 to 10 seconds. i want to have a light sensor so it only works during the night. i guess the exact thing i want is like those childrens balls that when you bounce they flash for a few seconds. i tried buying one and wiring the two leds together to stop the fash but as you can notice my skills with circuits are non existant. please someone help!! 



6 years ago

There is a program available to simulate and calculate 555 timers and their values for both timing and flashing purposes.
The link will take you to where you can download it.
I've found it to be really helpful, although a bit technical.

Like Jack said, you'll want to run it in monostable multivibrator mode. This type of circuit essentially turns on for a certain amount of time (based on the capacitor and resistor values used) and then turns off.
When you run the program, it'll ask you if your using a CMOS 555 chip or not. If you are, tick the box, then select the voltage of the battery, power supply, or whatever it is you want to run it on.
Then, click on the tab that says "monostable" , and enter the time in seconds you'd like the 555 to stay on in the box on the bottom of the window.
If you then look at the circuit, it'll display the values and components you'll need to make this circuit work. Your positive output comes out on pin 3, and that goes to whatever you're powering. Then, simply hook the negative lead of the device you want to power to the negative lead of your power supply.

Also, just a note: the values you use for your capacitors should be exact. But you can "fudge" it a little with your resistor values, as long as the time doesn't have to be exact. For example, if you want to time for about 10 seconds, the value of the resistor you'd use with a 1 uF capacitor would be 9.09 M. (which isn't sold in stores) But you can just go to 10 M. This'll give you a time of 11 seconds, but that's not really that big of a deal. You can also change the value of the capacitor you're using. (Ex, you can use a 470 uF cap and a 10k resistor to get 5.17 seconds, or you can use a 4.7 uF capacitor and a 1M resistor to do the same thing.) If you need the timing to be exact, you'll need to mess around with different capacitor and resistor values until you find a set that gives you a common resistor value.

Hope this helps!

Jack A Lopez

6 years ago

I think the circuit you want is called a "one shot",  or  "monostable multivibrator", by those of us who like words with lots of syllables.

I suspect you don't really care what it is called, but knowing these secret words  ("one shot" and   "monostable multivibrator") may help you to find an easy-to-understand circuit that someone else has published.  For example, I found what appears to be a whole bunch of links to such circuits, here:


6 years ago

Drive the LEds with a 555 timer triggered by an LDR light sensor - Should only cost a few $ Lots of information for 555 circuits on the web.