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Can i power and code the arduino uno by a 5v usb cord?
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Leighton Buzzard, UK
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yup - assuming the USB is connected to your PC
it's how I do it all the time! smiley
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The uno consumes very very little power, usb supplies 500ma i've not done the calculations but you should be able to run at least a couple hundred of them (and a few hundred more if you remove everything except the atmega chip) ..

The linear regulator is a huge power waste, bypass that and supply 5v direct it would use even less power smiley

http://forum.arduino.cc/index.php?topic=83612.0

claims

Quote
From the spec sheet:

• Power Consumption at 1MHz, 1.8V, 25°C
– Active Mode: 0.2mA
– Power-down Mode: 0.1μA
– Power-save Mode: 0.75μA (Including 32kHz RTC)



500/0.0002 amps

So that's uh..

250,000,0

A lot of chips you could run from a 5v USB supply, but with the regulator, the chip for USB communication add it all up, its still a lot of uno's.... off a 5v usb supply.
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I hav a drone that has a usb video record slot.....i was gonna put blinking police lights on drone, powering the arduino via usb ....will that work
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How many volts will the digital pins then supply.... on the spec sheet its says the input voltage 7 to 12v.....usb supplies 5v how can it run with 5?
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if you power through the power connector it can handle 7 to 12 volts, drops it down to 5
if you power through USB - it's already 5 so nothing else required smiley
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Thanks how many volts will come out of the digital pins with usb powered
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USB supplies 5V+/-some %, say its 5%
Thus the USB range is 4.75V-5.25V. Call that Vcc.
Output pins will then supply up to 20mA at no less than Vcc-0.8V per the data sheet.
5V -> 4.2V,  so 4.75 -> 3.95V. You will find the output will be closer to Vcc when the current draw is less.
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Also, regarding Reply #2, the Uno runs at 16 MHz.  Per Table 29-9 of the 328P datasheet, the device draws 5.2 to 9mA at 8 MHz, 5V. 16 MHz would be higher (not spec'ed). Current draw triples from 4 MHz to 8 MHz, so doubling from 8MHz to 16 MHz a similar jump from 5.2/9mA up to 15.6/27mA might be expected.

The ATmega328P draws current, the ATmega16U2 draws current, the power LED draws current, the 3.3V regulator draws current, the Vin/USB comparator draws current - did I miss anything? All those add up, so at a steady state condition with no IO loads, you will probably measure 15-20mA being used.
500mA/(20mA/Uno) = ~25 Uno could be powered from 1 USB port.
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Arduino for Teens available at Amazon.com.

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You can also run the Uno from a USB wallwart:
Here are some examples
http://www.amazon.com/s/ref=nb_sb_noss?url=search-alias%3Daps&field-keywords=usb%20wallwart#/ref=nb_sb_ss_i_0_11?url=search-alias%3Daps&field-keywords=usb+wall+adapter&sprefix=usb+wall+ad%2Caps%2C290&rh=i%3Aaps%2Ck%3Ausb+wall+adapter
Similar can be found for car use
http://www.amazon.com/s/ref=nb_sb_noss?url=search-alias%3Daps&field-keywords=usb%20wallwart#/ref=nb_sb_ss_i_0_11?url=search-alias%3Daps&field-keywords=usb+car+adapter&sprefix=usb+wall+ad%2Caps%2C290&rh=i%3Aaps%2Ck%3Ausb+car+adapter
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Arduino for Teens available at Amazon.com.

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Srry but u confused me alot lol.....will i be able to run the arduino and hav 2 red and 2 blue leds blink using my drone usb port?
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Will i be able to run the arduino and  2 red leds and 2 blue leds blinking off of my drone usb video recording 5v port?
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The drone puts out 5V on USB cable? 100mA or so?
Yes, you can run the arduino from that.
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It puts out 5v and probly over 100ma because i already put 8 leds on it before each at 20mA
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