what i want to do is create a very simple led sign. it consists of 80 leds. i would like to have it charge in the day, then power at night. i am wondering what kind of battery i need, the type of schematic i would need, and if i can do this withought resistors. i am on an extremmely low budget. also, car batterys are plentiful. people throw them away like nothing. can i use a car battery? if you would like i can upload a drawing of the idea i have.


if you must know, it is for an led throwie project i have in mind. instead of having lots of little leds, i could have one sign. and i could place this on a building or somthing.

also, to try to visualize this, imagine a sign, saying urban ninja. urban, containing 43 leds, and ninja, containing 37 leds. i dont need it blinking, or moving. all i want is it to last a long time.

 

also, i meant that if i can do it with out resistors for each individual led.

 

5 red LEDs in series would need a single limit resistor of around 270 ohm with a 12 volt supply.
5 Green or yellow LEDs in series would need a single limit resistor of around 150 ohms
3 white LEDs in series with a 12 volt supply would need around 100 ohm series resistor
All made on the assumption that there is a 12 volt supply.. around 12 - 15mA thru the LEDs, Red LEDs with 1.7 volt forward drop, yellow and green with 2 volt forward drop, and white with 3.5 volt forward drop.
Several banks of these series strings could be wired up in parallel to give you your display.

 

i think my mind just imploded. how would i go about doing that? i still want it to charge during the day.

 

again, i know nothing of electronics. about the only thing i know how to do is, mess with leds.

 

Heres the LED array for red or green or yellow LED's
This doesn't include charging or Auto night day switching....
Can you see why using the Series/parallel array would work, and why if would be 5 times more effiecient than single resistor/LED's off a 12 volt battery..?

 

thanks man, i think i understand now. ill just google around for some charger stuff, and figure it out from there. i have another question, that is for a different project, ill ask in another thread. its completely different. thanks gadget.