Is this correct?

Using Arduino Networking, Protocols, and Devices
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This is from http://arduino.cc/en/Tutorial/MasterReader

'If powering the Arduinos independently is an issue, connect the 5V output of the Master Arduino to the VIN pin on the slave.'

Is this right, i thought VIN had to be at least a few volts over 5 volts for the regulators? I'm asking because if i can use my 5volt supply into VIN it would be more convenient for when i want to use the USB connection for reprogramming.

and while i'm here, where do i change the IC2 pin numbers for the clock and data.

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There are three ways to supply power to the Arduino - the USB port, the barrel jack, and the Vin pin. The USB port will supply ~5V power. The barrel jack needs ~7V because that goes through the voltage regulator. The Vin pin expects the voltage to have already been regulated down to 5V.

I'm asking because if i can use my 5volt supply into VIN it would be more convenient for when i want to use the USB connection for reprogramming.

How? The barrel jack doesn't interfere with the USB port. The power into Vin MUST be regulated.

and while i'm here, where do i change the IC2 pin numbers for the clock and data.

With a soldering iron and great care.

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Well i don't know how that got confused. Sticking to the power. Vin is an input on the header as well. Next to the two grounds the 5v/3.3v and reset (on the uno). Forgetting about the barrel jack. But they are the same input yes? Vin and the barrel jack?
I am powering my board form a bigger supply this is fed straight into the 5v pin on the arduino. It works fine. If instead i put that 5v into the Vin pin as the page on IC2 seems to suggest i can, will it still work? (by work i mean carry on doing what it was doing correctly before i.e. turn on)

I have a feeling i'm not getting this question across very well.

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What is the difference between the 5v pin and the Vin pin then. I thought their was a difference your saying their isnt?

I thought if i put 7 volt on the Vin pin (i have never done this) i would get 5V on the 5v pin 3.3v on the 3.3v pin and and automatic switch over from the usb power. Or is that only specifically on the barrel jack it's self?

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It's starting to dawn on me that i may have been doing it wrong then for some time. I've always provided the 5v in the 5v pin not Vin.
I'm guessing it's safer then to use Vin?

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The power into Vin MUST be regulated.

Sorry Paul, the Vin input is for unregulated voltages { one all today :slight_smile: , private joke}

I've always provided the 5v in the 5v pin not Vin.

Yes that's the right way to do it.

I'm guessing it's safer then to use Vin?

No, that way you get a reduced Vcc and so you might overload the voltage input on the pins as it will be less that 5V.

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Thanks Mike, now to get back to what i was doing before that confused me, which it did for a minute.

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Grumpy_Mike:

The power into Vin MUST be regulated.

Sorry Paul, the Vin input is for unregulated voltages { one all today :slight_smile: , private joke}

OK private jokes aside, exactly what voltage or current and A/C or DC should be put in at the VIn pin then ?

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It should be DC, and any voltage between 7V to 24V. The lower the voltage the less heat will be dissipated in the internal voltage regulator and so the more current you can draw from it.

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Back to this question, maybe I missed the answer:
"and while i'm here, where do i change the IC2 pin numbers for the clock and data."
These are hardware specific pins off the ATMega328, which are connected to A4 (SDA) & A5 (SCL).

The Vin pin connects to the input of the 5V regulator, and 5V is the output pin.
I need to check the schematic to be sure - there is a reverse polarity protection diode at the output of the barrel jack connector, Vin may connect after the diode as well.

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