On a recent project for DIY Under Bed LED Lighting I found myself in a bit of a power conundrum. I had a strip of 5V LED lights that required around 7 amps to run at full brightness. I didn’t want two separate power supplies powering the lights and the Arduino UNO and I didn’t want the Arduino powered by a battery and I didn’t want to add a DC to DC converter to boost the voltage. I know, I seem pretty picky here!
Since the Arduino UNO’s absolute minimum input voltage (per the specs) is 6V, how will I get this thing powered off of one single 5V power supply in the simplest way possible?
Well, It’s much simpler than it sounds. The Arduino UNO itself actually requires 5V to operate, so why does it ask for more?
The Arduino performs it’s own voltage regulation on the power supplied through the power plug, hence requiring a little more power than needed to be able to regulate it to a proper 5V.
What can we do to get around this? Bypass of course! We will be bypassing the built in voltage regulator with absolutely no board modifications necessary. We can do this because Arduino has already bypassed their own voltage regulator for us!
When you plug your Arduino into your computer via the USB port, you don’t need to connect it to any other power supply, the computer supplies a regulated 5V to the Arduino and the Arduino trusts this power supply so it bypasses it’s own voltage regulation.
The Arduino UNO 5V Workaround
Do this at your own risk. The Simpleton assumes no responsibility if something should go wrong! It works fine for us but as we all know, results may vary.
So the fix that I am using is to supply my own regulated 5V through the USB port. To do this, we just need a USB Type B cord that we can cut. You might have a spare laying around from past printers or you can buy one if necessary.
The pin-out on USB plugs is standard.
So with that being said, we need to attach the wire from Pin 1 to our 5V power source and we need to attach Pin 4 to our power source Ground. I will solder these directly to the prototyping board to allow them to draw 5V from the power supply that I already have hooked up to the board. Pin's 2 and 3 need to be terminated and isolated so you don't get any stray voltage or signals through them, take them completely out of the circuit. Now plug in the power supply, hook up the Arduino to the new power USB and you should have a fully functioning Arduino Uno.
A word of warning: Use a good quality power source that is accurately regulated. Check the voltage yourself using a multi-meter. Voltage other than 5V supplied to the Arduino this way can and will destroy your Arduino!
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