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Author Topic: Do I Need Resistors?  (Read 743 times)

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Offline SylvestreTopic starter

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Do I Need Resistors?
« on: January 23, 2012, 07:39:00 PM »
Hello everyone,

I am planning to connect 8 LEDS in parallel to the 3.3v regulated area on the Axon II.  Do I need to still put resistors between the Axon II and the LEDS.

Also would I be better off connecting the LEDS to 5v regulated?

Thanks

Jason

Offline Gertlex

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Re: Do I Need Resistors?
« Reply #1 on: January 23, 2012, 11:06:50 PM »
I don't think there's a good reason not to have a resistor.

You also definitely don't want to use the 3.3V pins. Per the Axon 2 pages
Quote
The Axon II also has a special regulated 3.3V output bus, great for components or sensors that require this low voltage. This pin cannot supply more than about 73mA, or 90mA if you aren't using USB.


20 mA per LED is typical.

You can use this calculator for resistors + LEDs: http://led.linear1.org/led.wiz
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Offline SylvestreTopic starter

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Re: Do I Need Resistors?
« Reply #2 on: January 27, 2012, 06:10:49 PM »
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20 mA per LED is typical.

Yeah that's what it says on my datasheet.

Quote
You also definitely don't want to use the 3.3V pins. Per the Axon 2 pages

What do you pins do you recommend I use? 5 volt or unregulated? (battery supply is 12v)


Quote
You can use this calculator for resistors + LEDs: http://led.linear1.org/led.wiz

Thanks for that.  Very helpful. :)

Offline Gertlex

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Re: Do I Need Resistors?
« Reply #3 on: January 27, 2012, 06:17:57 PM »
5V will work, and so will 12V.  The one consideration that comes to mind is that the 5V is limited in current by what the voltage regulator can supply... but you're not going to be near that limit with the number of LEDs you're planning... (I think that limit is ~1 A without a heatsink? But don't quote me :) )
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Offline SylvestreTopic starter

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Re: Do I Need Resistors?
« Reply #4 on: January 27, 2012, 07:23:21 PM »
When I put my specs into the LED calculator, it put the resistors after the LED (negative).  I've heard of this method before, but I don't understand how it works.  Can someone explain that to me?  If I wanted to I could put it in between the 5 volts and the leds, right?

Thanks

Offline Gertlex

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Re: Do I Need Resistors?
« Reply #5 on: January 27, 2012, 07:30:25 PM »
Resistor location doesn't matter (aka before or after LED).
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