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Topic: Powering Arduino makes a difference? (Read 638 times) previous topic - next topic


I think current limit could be in effect - the 500mA USB specification is not the default current limit, its the maximum limit a USB host is expected to supply.

USB is supposed to negotiate current requirement via a request packet of some sort - I have no idea if the Arduino does the right thing to make this happen (I suspect most USB hosts just supply 500mA anyway from the start).

[Usually pattern sensitivity with switching lots of LEDs is a supply or decoupling issue - you have adequate decoupling for the shift register?]

By decoupling, do you mean placing a small capacitor between Vcc and GND (just looked it up). I didnt do that, Would a 1uF work? That is the lowest I have :/



1uF is much better than nothing so use that, but most likely they won't be ceramic capacitors.

It is likely that the external supply had enough decoupling for your chips but you should always add your own. For best high frequency response they should be ceramic capacitors between 0.1uF and 10nF.


I noticed that LEDs attached to pins flashed when I uploaded sketches http://arduino.cc/forum/index.php/topic,72454.0.html.
People put this down to a board design fault.

Perhaps you are getting pulses, when you upload, that are messing up your shifting?
Maybe that is why resetting gets things going - just a thought.

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