Simple LED auto-turn off circuit

[duda123]

Hello guys! I need some helping building a circuit that works like this:

I have a button (the one that do not "lock" once you press it, but just goes back to the original position) and when you push it, a LED must turn on for 5-10 seconds (not a random value, but any fixed value from 5 to 10 seconds) and then it turns off.

-------------------------
<Push button>
<Led turn on>
<5-10 seconds>
<Led turn off>
-------------------------

Thanks a lot

 

[SPDCHK]

Hello guys! I need some helping building a circuit that works like this:

I have a button (the one that do not "lock" once you press it, but just goes back to the original position) and when you push it, a LED must turn on for 5-10 seconds (not a random value, but any fixed value from 5 to 10 seconds) and then it turns off.

-------------------------
<Push button>
<Led turn on>
<5-10 seconds>
<Led turn off>
-------------------------

Thanks a lot

Try THIS link. It will calculate the component values for you

 

[lloydi12345]

you can also use a microcontroller to make one but for simplicity use 555 timer

 

[awt]

555 timer (monostable), simple as A B C...

 

[KMoffett]

Do you want just the LED to shut off, or power to the whole controlling circuit too?

Ken

 

[duda123]

Ken, it doesn't really matter if the whole circuit shuts off or just the led... i'm really noob to electronics, and i need the easiest circuit someone can teach me how to build

I'll try the link SPDCHK posted! Thanks


-------------------------------------------

EDIT: Where do I add the LED in that circuit? =\

 

[Reloadron]

The attached circuit should do what you want. It is the basic 555 mono stable (one shot) circuit that has been mentioned. As drawn, depending on the setting of R1 the LED will illuminate for up to about 11 seconds, the time is adjustable by R1. The circuit can be powered from between 5 and 15 volts. The LED I Limit resistor value will depend on the voltage supply and the data for the LED. The few parts can be had just about anywhere.

Ron

 

[duda123]

Wow! Thanks a lot for that!

You said that LED time is adjustable by R1... but how can I adjust it? The bigger the resistor value, the smaller the time or the bigger the resistor value, the bigger the time?

And how can I calculate LED I Limit resistor value?
The voltage supply is going to be 6v (2x 3v battery) and the LED voltage drop is 1.7 volts.

Dude, THANKS A LOT for you help! That circuit is all I needed! Thanksssss!!!! Thanks!

 

[Reloadron]

Wow! Thanks a lot for that!

You said that LED time is adjustable by R1... but how can I adjust it? The bigger the resistor value, the smaller the time or the bigger the resistor value, the bigger the time?

And how can I calculate LED I Limit resistor value?
The voltage supply is going to be 6v (2x 3v battery) and the LED voltage drop is 1.7 volts.

Dude, THANKS A LOT for you help! That circuit is all I needed! Thanksssss!!!! Thanks!

No problem. It's a pretty common circuit. R1 is a variable resistor having a range of 0 to 1 MΩ. R1 forms a RC (Resistance / Capacitance) network with C2. So R1 and C2 form a timing network. For a circuit like this it becomes the on time at the output of the 555 will be about 1.1 * (R * C) so what you have is a maximum of about 11 seconds adjustable down to nothing. C2 is a .0000010 value and R1 is 1,000,000 at maximum. This is not an exacting science because a 10 uF cap is subject to tolerance as is the resistor.

The 555 timer chip is a good choice for doing something like this for several reasons but an important reason is it can source about 200 mA which is adequate current to drive most LEDs eliminating the need for a transistor driver and more additional parts.

Moving along to the LED. Well we know that if we apply 6 volts to the LED it will have a really bad day. Now you mention the LED has a forward voltage of 1.7 volts. That is 1/2 the story. The LED also has a forward current rating and that is something we need to know. Here is how things for the LED work out. Just as an example we will say the LED forward voltage is 1.7 volts, we will also say the LED forward current is 15 mA (.015 Amp). We will get:

Vsupply - Vled / LED Current or 6 Volts - 1.7 volts = 4.3 Volts / .015 Amp = 286.66 Ohms

You won't find a 286 Ohm resistor so an off the shelf 270 Ohm will do fine. That is a guess for your LED.

In the circuit I posted you would adjust R1 for the desired on time of the LED and set it & forget it or you could for example try a 500 KΩ fixed resistor and live with the timing.

You said that LED time is adjustable by R1... but how can I adjust it? The bigger the resistor value, the smaller the time or the bigger the resistor value, the bigger the time?

The higher the resistance, the longer the time (LED on time).
Ron

 

[duda123]

Wow! You really helped me a lot! That was really nice!
Thanks! Thanks! Thanks! Thanks! Thanks!

 

[Reloadron]

Hope it works out for you. Any questions just ask.

Ron