Color shifting with the Nano and tri rebel rgb

[dgregory]

Simple question if i can explain it well enough. I want to have a tri rebel rgb wired with all three die in parallel to a dip switch. Each die will its own resistor based on its current needs. My question is what happens if i turn on two die at once? Will the resistor needs change? Won't each die be getting half the current? Would this setup require having two resistor choices per die, one for running them each by themselves and one for running them with a second die? If that's true, i suppose i could put a spdt switch on each + lead for each die. I could switch each one betwen "lone gunman" and "buddy system" mode. That's a lot of switches and resistors to cram fu.

Is the an easier way to do this?

[dgregory]

Oh yeah, the other part. Is this even worth doing with a nano and 3.7 volts? Its only a 3w led and i can put 2 mA through it, which should be enough to get a bright blade even when using the blue and green die together (1 mA each).

[Lord Dottore Matto]

Both dice get 3.7 V if run in //, but they each get half of the Amperage. So, if you have the Nano pumping out 1A and with one die running, it will get 1A...2 dice will get 500mA each. The only die necessary to resistor is the red since the vF of the G & B dice are very close to 3.7V.

[dgregory]

So if i use an 18650 with 2.6A of current, the nano will pump out its maximum of 2A correct? If that's the case, is one resistor setup okay? The red die, for instance, will get 3.7 v either way. When lit with a second die it'll get 1A. By itself it'll get 2A. I would think the single die setup would require more resistance. If i put a resistor on the red die to handle 2A and it gets 1A in a two die setup, wouldn't it be dimmer than it could be with a resistor for 1A?

[TrypWyr]

Maybe I'm misunderstanding but the NB doesn't have a voltage regulator, so it's not "pumping out" any amperage, is it? If you don't use the drive function on the NB, then the LEDs are just pulling the current directly from the battery. In that case, if the 18650 can discharge 2.6A, then if two dies are active and both need 1A, they should be able to get it, right? You would just be depleting the battery almost twice as fast with two dies vs a single active die.

Sorry if I'm wrong here, the intricacies of electronics still puzzle me sometimes.

[dgregory]

I don't know. I've never put more tan 1.4A trough the nano. It has a 2A max so maybe a 2.6A battery is a bad idea. I don't want to fry the nano or a tri rebel.

[Silver Serpent]

You're confusing mAh with mA. You don't want to run more than 2000mA (2A) through the NB at a time. Meaning, don't use main LEDs that are using more than 2A of total current. Two LEDs at 1000mA each in parallel is fine.

mAh is a measure of energy storage. It's like the size of the gas tank on your car. A 2600mAh battery can (theoretically) provide 2600mA of power for 1 hour. Or 5200mA of power for 30 minutes. Or 1300mA of power for 2 hours. You get the idea.

There's also the issue of maximum discharge allowed by the battery. Most of the li-ion cells are limited by the PCB on them, assuming they're protected cells. An 18650 cell will usually support 3A discharge or more before tripping the PCB.

The LEDs are only going to draw the power they need, so if you have 2A worth of LEDs drawing power, then that's all that will be pulled from your battery pack. Don't exceed the 2A limit on your main LEDs, or you'll risk damaging the Nano board.

[dgregory]

Thanks everyone. That's much clearer. I think i'll be okay with one resistor setup per die. If the resistors keep the current and voltage under the limits for each die, it should be fine. I assume i should resistor them like they'll be running by themselves. I'll just have to test them and see what effect it has on blade brightness.

[dgregory]

Here's the diagram for what I'm thinking. It will isolate the red, green, and blue leds through a DIP switch. The switch will provide power to the main and accent leds for each color. I'm hoping, if this works, that I can change the color of the blade and crystal chamber together. I imagine I'll have to kill the power to shift colors. The real problem is the space that the control board and resistors will take up. I'll just have to make a longer hilt. I'm planning to mount all the resistors and DIP switch on a perf board to keep them tidy and secure.

Also, the resistor calculator said I needed a 2.2 Ohm, 2 W resistor for the Red. The vF is 2.3 volts at 700 mA. Seems to be a weird resistor value.

Hopefully the diagram is legible.

[Silver Serpent]

Your diagram looks fine. I have a couple things to mention:

1. DIP switches are generally used for low current applications. You'll be feeding 1000mA or 700mA through each one. Hopefully your DIP switch is robust enough to handle that much current. If not, you may want to look for some small slide switches.

2. Don't turn on all three dice at the same time. The Nano Biscotte board has a limit of 2000mA for the main LED at one time. With 1000mA for blue, 1000mA for green, and 700mA for red, you can only safely run one or two dice at the same time.

Your resistor values are spot on. They'll work just fine.