LED advice

so, i'm a pretty avid fan of our local roller derby team (HKRG BABY!), and i belong to a group of super fans who focus on doing a lot of weird crafting and costuming and other such insantiy for the bouts.

so, i'm wanting to make some pretty fancy signs for next year's derby season that will  light up. i've got some plans to use some EL wire/tape and the accompanying equipment but i've also got some other sign plans that would probably be cheaper/easier to make using LEDs instead.

so, basic premise is to have a sign that would be able to light up some cut out letters separately and sequentially. i know how to make the sign itself so that's not the issue, what i need is a method to cheaply and easily make the letters light up in sequence.

so it's a 3 letter sequence (let's use D O A as an example) that progresses at the normal speed that you would imagine a large group of people chanting a 3 letter call sign to go. so the D would lights up for a second or two, one-two second pause, O lights up for a second or two, one or two second pause, then the A for a second or two, lather rinse repeat.

i'm imagining that each group of LEDs for each letter would be wired in series, then each group would be wired to whatever circuit would be needed to make the lights cycle. i'm not sure exactly how many leds will be needed per letter, but maybe between 10-20 of them per segment?

i'm going to have several of these types of signs (all 3 syllable chants) so i'd like it to be something that's easy to repeat and not terribly expensive (i'm a derby nut, but there is a line where cost kind of gets stupid)

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crapflinger (author) 5 years ago
ok, switching gears. need a quick diagram for a sound activated LED circuit. no more than 10 green LEDs. i'd like maybe to have it be selectable? like off/on/sound activated. and probably some parts suggestions.
Well, here is an overly simplified hackneyed version :-)

Sound Act LED.bmp
Honus5 years ago
I'd use an Arduino and simply turn on each letter in timed sequence using a transistor (a TIP120 would work.)

So what you do is connect a transistor to a digital out pin (be sure to put a resistor between the output pin and the transistor) then set the output pin HIGH to turn on the letter, have a delay, then turn on the next output pin high, and so forth.

If you would like a schematic or a code sample just let me know.
crapflinger (author)  Honus5 years ago
yeah, looking at other projects most people use transistors or mosfets (advantages of each?). after looking at a few schematics of other projects they're making a bit more sense. they seem to be working like a mechanical relay, but doing it non mechanically.

so they're switching higher current/voltage (whatever) than the trigger voltage/current.

i've been looking at this tutorial from ADAfruit for their analog LED strips since that's basically what i'll be ending up with
so, my current understanding of the transistors or mosfets in this application:

you would supply the LEDs with the proper voltage/amperage from an external source (or from the 9v source from the arduino). you would use the transistor/mosfet to switch to ground on the LED circuit by setting an output pin on the arduino to high (or if you were doing PWM you could use the PWM pins to control the proper output) right?
Yep- you got it. The advantage of a mosfet over a darlington transistor (TIP120) is less voltage drop- both will work just fine for your application. I always seem to have plenty of TIP120s on hand so that's what I use.

There's another transistor usage tutorial here-
crapflinger (author)  Honus5 years ago
ok, so this whole thing is going to be battery powered. based on the design each letter will have probably 10-15 LEDs (probably high brightness green, though, they will be illuminating through a frosted/translucent green film of some kind anyway, so maybe white would work just as fine?). typical derby night is 4 hours but the signs would usually not be on for more than 5 minutes at a time or something like that. so, like a rechargable 9v-12v battery for like a power tool or an RC car would be smarter than a regular 9v square battery to power both the arduino and the LEDs?

Either color LED would work just fine- the green will look more green than white LEDs behind green film but the white might be a bit brighter. The rechargeable battery would be the way to go- a small 9V transistor battery won't be able to provide enough current for all those LEDs.
crapflinger (author)  Honus5 years ago
something between a 7v and 12v lipo with 1000+ mAh rating right?
That would probably work just fine. The voltage will depend on how you wire up your LEDs.
crapflinger (author)  Honus5 years ago
if time decides to be my friend again any time soon i'll try to draw something up in visio or something to make sure i'm on the right track
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