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Topic: Correct way to wire up 9V >> Arduino >> 5V OUT (Read 1 time) previous topic - next topic


What's the correct way to wire up a 9v circuit IN to the Arduino mini to power it, and a 5v circuit out to power sensors, accessories, etc...?


Jan 27, 2007, 02:18 am Last Edit: Jan 27, 2007, 02:18 am by scottmcleod Reason: 1
NVM. Found it. +9v to Pin 20, -ve to Pin 19. +5v comes from Pin 17, and the ground for the 5v line comes from Pin 3.


Why won't the USB work?


USB works, only if you connect the USB power as well. Weird?


The FTDI chip that handles the USB communication (and the USB to serial conversion) is powered by the USB connection.  I guess the assumption is that if there's no USB connection, you don't need any USB communication.  Is there a situtation in which you'd want to communicate over the USB connection without supplying power over the USB connection?


Exactly :)

in the usb world there are 2 category of devices: bus powered and self powered

when arduino is plugged in is bus powered while when you plug the power supply and move sv1 only the ftdi chip is bus powered and the load is quite small (a few ma)

there is only one case where this can be annoying: when the ftdi reports a power need of say 100ma but it needs only 10 (because the FTDI chip is the only one powered) on certain machines the OS might say "sorry i cant accomodate that because there is too much power already used on the bus"

it's a remote event that can be fixed using an active usb HUB...



Jan 29, 2007, 03:54 am Last Edit: Jan 29, 2007, 03:57 am by scottmcleod Reason: 1
Nono, what i'm trying to do is...

USB Board

 |   |     TX/RX wires


Sensors & other things that need +5v

Which pins will DELIVER +5v OUT if I put +9v IN onto the arduino?


I'm not sure I understood your diagram.  What "USB board" mean?

All the pins on the Arduino board will use 5 volts for HIGH (0 volts for LOW, of course) except for the +9V pin.


Yes, but does the Arduino Mini convert 9v > 5v inside of it for use on sensors & digital pins? I was looking at the schematic and there's something that does some kind of conversion in the top left of that PDF of the schematics.

The USB board is the USB stamp that is used to interface the mini to a computer.


Yes, there's a voltage regulator that converts the 9 volts you power the board with to 5 volts for the digital pins, etc.

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