Using Barrel Jack & Vin

I have an UNO running off a wall jack rated at 5V.

I just tested the V betwen the 5V & GND on an UNO which came at 3.5V.

Then I tested the V between the Vin & GND on the UNO and got 5.2V.

I believe I read somewhere that the Vin is indeed the + terminal to use when using the barrel jack.

Is this correct?

Yes. You need about 7.5V at the barrel jack.

Center pin on jack --> protection diode --> Vin --> regulator --> +5

The diode drops the voltage by ~0.6V and the regulator drops it another ~1V (or more).

https://www.arduino.cc/en/uploads/Main/arduino-uno-schematic.pdf

jboyton,

Are you explaining to me how the barrel jack gets 7.5V but the diode drops it to 7 and then the regulator drops it to 6? wait, Im missing a volt :slight_smile:

diode drops 0.6 to 0.7, leaving 6.9 to 6.8 at the regulator input, 5V comes out of the regulator.

Thanks!