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Topic: is powering an ATmega386P with usb cable and USB AC Charger plug save? (Read 1 time) previous topic - next topic


When making your own barebone Arduino, would it be save to power it with usb cable connected to a USB AC Charger plug, connecting VCC and GND from the usb cable to the according ATmega pins?

or do you need a power regulator?

My usb AC adapter plug has this inputs and outputs:

INPUT: 100-240v 50-60Hz 0,15A MAX
OUTPUT: 5,0 V 1,0 A

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Yes, you can power your circuit from just the USB cable only, same as if you had an Uno or Duemilanove that was powered from just USB cable.
You only get 500mA.
There are many devices out now that plug into USB ports for power - little keypad lights, fans, battery chargers ...
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.


so no power regulator is needed between usb and Atmega386P? ok nice

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Yeah keep in mind some USB AC chargers can put out more than 500mA, my Motorola Droid Bionic's charger claims 850mA, my old Blackberry AC charger claims 700mA... I think the Apple iPad charger can push 2.1A (and it's 5.1V I believe?)



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So those would fry the ATmega328?

No, the amount of current drawn from whatever source is determined by the device drawing the current, a arduino in this case. The fact that a voltage source has more current avalible then the load requires does not 'force' a higher current into the device. It's ohms law where the resistance of the load determines how much current will be drawn from a given voltage.

Your 120vac AC outlet on the wall can power a vacuum cleaner or a night light, and they both don't draw the same current from the outlet, right?


So actually you wouldn't need the 7805 power regulator and the 0uF capacitor when using an usb cable to power the thing. (now that I think of it, this is used for 9v power supply)

Mmm, nice so a 16 MHz external clock and 2 two 22 pF capacitors (if you want it running at 16 Mhz) powered by usb would just do the trick?

adding a reset button with a 10k ohm pullup resistor would be wise to.

And I could just upload my sketches with this http://store.arduino.cc/eu/index.php?main_page=product_info&cPath=11&products_id=143

OK thanks to all.

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