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Topic: using Uno to multiplex 200 common-cathode RGB LEDs, not sure about resistors (Read 5966 times) previous topic - next topic

Grumpy_Mike

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used a 9 volt battery and limited the current with resistors, the battery would last longer than it would without the resistors?

No please do not try this it will not work.
The only way to get the voltage down is to use a regulator NOT a resistor.

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If so it might make sense for me to rig up a set of those in parallel.

Wiring batteries in parallel is never a good idea because they cross charge each other. Series connection is the way to go.

marklar

200 LEDs is quite a bit to run on battery power.  I use one of these 12v batteries ..  http://www.sears.com/shc/s/p_10153_12605_00911221000P?sid=comm_sears_other
... and four 5v 12V car adapters 1.2 amps each and it only runs 70 LEDs for an hour. 

Providing more details on what your end goal is would help.  You say you want this to put on two helmet visors and needs to be see through. I would suggest you test the minimum size / separation to see through with a few LEDs and compute the maximum LED count from that.

I hope the battery details help. 



mschn

I'm undertaking a similar project and will be using one or two 11v LiPo batteries. These http://www.hobbypartz.com/83p-4000mah-3s1p-111-20c.html are 4000mAh at a very reasonable price. You'll have to buy a special charger for them but if you're anticipating any longevity of your matrix I think it would be a good option.

Grumpy_Mike

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So am I off base in assuming that if I (hypothetically) used a 9 volt battery and limited the current with resistors, the battery would last longer than it would without the resistors?

No that is wrong. Do not put a resistor in line with the battery.
At best it will just heat up instead of the voltage regulator, at worst it will stop it working.

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