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[on:]

Hi all.....
 what is the difference between Vcc, Vdd, and Vpwr? 

[Reply #1 on:]

Different logic families use different Vxx to represent the positive supply pin.
With respect to Arduino, with everything powered from 3.3 or 5V, there is no difference.

[Reply #2 on:]

Thanks but for a mosfets and solenoids is Vdd different than Vpwr?

[Reply #3 on:]

No.  A solenoid is like connecting up a coil.
The + side will go to +12V say, the - will go to a LOGIC LEVEL, Low Rds, N-channel MOSFET Drain, the Source pin will connect to Gnd. Arduino will drive the Gate thru a 180 ohm resistor to limit arduino current flow into the MOSFET gate capacitance.
Put a 1N4001 diode across the + & - pins; anode on the -, cathode on the +. See the lower right hand example.

[Reply #4 on:]

well i guess i need to explain more... here is the problem... i am using an emulator for real arduino circuits and codes.... therefore there is nothing called a 12v source or 5 ... there is just VCC , VDD, VPWR etc... that's why i was asking for the difference

so if i am connecting a solenoid to arduino i need a mosfet and diode.... why??

[Reply #5 on:]

Most solenoids will need more than the 20-30mA output that an arduino can sink to activate it.
You could use an NPN transistor too, depends on the current you need to sink.

Go with VPWR.

[Reply #6 on:]

there is just VCC , VDD, VPWR etc... that's why i was asking for the difference

Those are just names, and they need to be defined/documented somewhere.    Sometimes "knowing" that Vcc is usually +5V, might not be enough, or using the name/label '+5V' might not be enough, because there may be more than one 5V supply and you need to know which 5V supply is connected to which IC.  (i.e., you might have Vcc1 & Vcc2, etc.)

It's like anything else on a schematic...  It helps relate the schematic to the physical circuit.

Typically with an emulator/simulator, you can assign connections/meanings of your choice to these names/symbols.