Arduino Uno Rev3 pinouts photo

[WizenedEE]

I find that the pins on the ICSP header (on the right) are useful for grabbing an extra +5/Gnd combination if I need to power other devices (or for hooking up a multimeter or logic analyzer).

I generally use the giant USB socket for a gnd to connect my multimeter to.

[opal_1970]

Hey thanks alot for sharing, this is really useful.

(cool, and I am the 1970^th person to view this)

[pitusso]

Have you already share this in the playground?
It's very useful!

[sellonoid]

Please pardon the somewhat off topic post....


I just bought an R3 Uno and it has the DIP processor.

Are the surface mount versions out yet, and are there any advantages to the surface mount types?

[CrossRoads]

Surface mount was used on Unos when DIPs where in short supply for a while.
Same die within each package.
Surface mount does allow access to two analog-input only pins, but they are not connected to any header pins on the Uno.
So really just a disadvantage when you smoke the chip by accident and need to replace it.

[Nick Gammon]

I like the removable ones. After all, if you test new sketches every day (as I do) then you will wear it out eventually. Rather than buying a new board for $30 I can replace the processor for $5. Similarly if I do something silly and burn out an output pin.

When you are ready to go you can buy one of the surface-mounted "tiny" versions that will be physically smaller and do the same things.

[tuxduino]

Thanks Nick, that photo is useful. A very good page on your site, too.

[NI$HANT]

JP 2 is for?

[Nick Gammon]

I wondered that when I was doing the picture. See this:

http://arduino.cc/forum/index.php?topic=83829.0

[BillO]

Thanks for the pictorial doc.

BTW, what is the scoop on why they the second access to A4 and A5 (SCL & SDA).  Why would they be needed twice?

[Nick Gammon]

On the Mega SDA and SCL are in different spots. I am guessing they wanted to make it so shields could be compatible with both the Mega and the Uno if they use I2C.

[CrossRoads]

paraphrasing Blazing Saddles:
"You said I2C twice."
"I like I2C."

[bperrybap]

I actually prefer what Seeeduino and iTeeduino did for i2c on their boards by providing a separate 4 pin header.
That way everything you need is there with a simple 4 pin connector/cable and you can still
use it even when a shield is being used.

--- bill

[nigeljohnson73]

Below is a modified photo of the Uno Rev3 board, with annotations about the extra meanings of some pins (not printed on the board):
Earlier boards are similar except that they don't have the ICSP header for programming the USB interface chip, and the extra SDA/SCL sockets for use with I2C.

Are the I2C pins on the D8-D13 header the same as the ones on A4 and A5? If so, are these in the same place as on a Mega because the A4 and A5 pins moved to D20 and D21 on the Mega and that's a pain for building a shield.

Thanks

[CrossRoads]

"Are the I2C pins on the D8-D13 header the same as the ones on A4 and A5?"
On Uno, Yes.

"are these in the same place as on a Mega because the A4 and A5 pins moved to D20 and D21"
No.
Mega has seperate functions pins for I2C, are not on A4/A5.