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1  Using Arduino / Motors, Mechanics, and Power / Using multiple switching voltage regulators on: November 19, 2012, 11:05:22 am
I just did a search and didn't see anything on the subject. Forgive me if this has been covered.

Normally I'd take a 12vdc source and use a switching voltage regulator to step it down to 5vdc. With this regulator let's assume it has a 1 amp max draw on the 5vdc side. If I added a second switching voltage regulator and connected the 5vdc rails in parallel, would I have a theoretical 2 amp max draw? Would I need some diodes between the regulators and their parallel connection?

Could I do the same thing with the DC legs of a bridge rectifier? Would they need diodes between the rectifiers and their parallel connection?
2  Using Arduino / LEDs and Multiplexing / Re: Need some help picking out and coding for 11 LEDs. on: October 22, 2012, 07:34:55 am
You'd have to use a transistor to control the current thru the LED, 40mA is max for an IO pin, and long term (or maybe less!) will damage the pin.
There is no current limit built if - if you don't limit it externally, it will burn the pin out.


That's what I was looking for. Thanks for all the info.
3  Using Arduino / LEDs and Multiplexing / Re: Need some help picking out and coding for 11 LEDs. on: October 19, 2012, 06:34:50 pm
Uno can do that.
Need 11 current limit resistors.
LEDs & resistors here
http://www.dipmicro.com/store/index.php?act=viewCat&catId=511
Pick resistor based on (5V - Vforward of LED)/.02 = resistance needed.

Browse Learning Section, or the Playground, for ShiftPWM, will let you fade up/down LED on any pin, and not just the 6 pins with hardware PWM.

9V battery only has 200-300mAH of power. Use 5AAs (7.5) into the  barrel jack instead, for 2000-2500mAH of power. Add a 6th if you want, will just into heating up the 5V regulator tho.
11 LEDs drawing 20mA = ~220maH by themselves when all are on.

Thanks for the great info. Am I correct in assuming that your calculation is based on dividing the voltage I need to dissipate by the max current draw of the LED, corrected for units of scale?   Is there a good explanation of reverse voltage somewhere that someone can point me to? Also what would happen if an LED had a working voltage of say 3.5v at 40 mA? The I/O pin on the board cannot output more than 40 and due to the losses associated with switching electronics I'd assume it would actually be a tiny bit less than 40 mA.

I accomplished exactly what I wanted to do without needing PWM at all. I've spent an abnormal amount of time working this project and relearning C after 15 years of booze erased all the time I spent in computer science in high school.



4  Using Arduino / LEDs and Multiplexing / Need some help picking out and coding for 11 LEDs. on: October 12, 2012, 12:31:48 pm
I spent about an hour searching for a thread that might shed some light on my project but didn't see one. Forgive me if you guys have been over this before.

I was given an arduino kit as a gift recently. I'll have to look when I get home to get the specific kit but I'm guessing its the UNO.  I'm looking to use it to control 11 LEDs that will run through a static visualization.  I've never coded for an arduino before but in the past I've written PHP, various forms of C, Java and currently write bash, batch and power shell scipts frequently. I've also got a pretty good amount of experience soldering and otherwise working with components as well.

I'm looking to put together a circle of 10 dim-able LEDs with one dim-able LED in the center .  On boot have them all together go from off state to full on state over the course of about a second. Then enter a loop where every 10 seconds one led at a time drops to the off state and then comes back up to full on state so that it looks as if the ring is spinning 1 full circle over the course of a second. If by default the unit I have can't independently control 10 LEDs, I'd be happy controlling them two at a time in parallel.

I'd like to power this project via a 9v battery adapter but I'm not sure if that will give me the juice needed.  Is there any reason not to? Do you have any suggestions for bright white dim-able LEDs?
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