I am designing a (hopefully) simple circuit. I've been reading for several days on this site and can't find all the answers I'm looking for. Just getting into this space so thanks ahead of time for any input you can give.

My circuit is battery powered (AAs or 9v, whichever will work)
I want it to function as follows, when a momentary switch is pressed I would like 3 white LEDs to fade on (let's say 2 second fade on) then stay lit for maybe 5 seconds then fade back out over 2 seconds. Timings are a little flexible.
The switch acts as a trigger for the timing circuit to start lighting the LEDs.

After reading the LEDs, 555s, PWM, Flashers, and Light Chasers Index page, I think I might be able to manage using PWM to get the fading LEDs but that only works when power is applied then removed. I need help with the switch/timer circuit.

I think we could run the LEDs at 10mA? They don't need to be super bright.
Also, with this circuit being "powered up" all the time waiting for a switch press, will this drain the batteries within a short amount of time?

 

With three white LEDs in series you will need a 12 V battery to get them to normal brightness, because each one requires around 3.5 V across it. If the three LEDs are in parallel, each with its own current limiting resistor, then a battery in the 6 V to 9 V range will work but the current draw will be higher. Either way, there is a way to do this without the complexity of PWM, using one of my favorite parts, the CD4060 CMOS oscillator/divider. Where are you located, and what is your skill set for acquiring electronic components and assembling small circuits?

ak

 

I'm in Missouri and am capable of building a circuit. I have done several small projects before but none of this level.

 

If you come an go to thrift stores and find 2 wireless home phones and us the battery packs. They should be about 3.7v each and you can wire them with a connector in series to get your PSU. You might want to look in to a circuit simulator and play around with different IC's to find what your looking for.

 

Ok. I'll check that out. You think that an IC is the best thing to handle the timing functions? I was hoping to make a small version that relied on as cheap of materials as possible but it sounds like using an IC may end up lowering the overall parts count. Are there any ICs I can look at specifically?

 

lm a newb and dont know a whole bunch yet, have you tried googleing or youtubing Fade on LED cicuit?
Also really look in to the simulator and fool around. With using a simulator I have made my own turn signal relays and servo controllers using only 555 ic