Arduino USB powering Arduino and 3.3v device

Which version of Arduino are you using?

Many have a 3.3v pin on them that you could use.

It's important to remember that the I/O on the Arduino will still be at 5v though.

Its the arduino Uno. i purchased from Maplins in UK yesterday. basically i was wondering if i can do this. i drew a diagram.

I appologise for the bad drawing but. can i do this. have the arduino and the Xbox 360 RF board (needs 3.3v) connected to 1 USB cable or will this cause problems?

Thanks

No worries. I have annotated your drawing with my suggested approach.

Forget about anything within the greyed out box area and consider adding the two wires I have added in:

that would be a better alternative. the only problem is that the RF module has 3.3v but you needed the zener diode to A) take it down to 3.3 and B) to prevent any voltage drops or something. it was to make sure the flow could only go to the Module and not come back. if i did that. i would risk burning the arduino out wouldnt i?

From USB is 5V nominal, with a 5.1V zener used as a zener it would drop the whole 5V and leave you nothing for the 3V3 board. A standard diode will drop about 0.7V so 5V would become about 4.3V but with USB it could be less or more than 5V.

The diagram that paulellison shows is utilizing the 3.3V output already available from the UNO and that is regulated so is just right for the board it is connecting to

The issue that is outstanding is if your device that is not specified can handle a logic 5V from the uno on its inputs and if not then there are a few simple possibilities you can use to integrate the UNO to your board. Without knowing the board it is hard to say. but options include

A couple of resistors to divide the 5V into 3V3 so perhaps a 1Kand a 1.5K would work.

2 diodes in series to drop about 1.4V has worked for many people

a level shifter with a transistor and 2 resistors1K to the base of the transistor from the UNO output and 1K between the collector and the 3V3 rail. take the output from the collector to the board needing 3V3. the emitter is connected to 0V.

all these of course assume your driving one way if the board needs 2 way then its a little different

let us know what the other board is and we could better advise

I think he said:

have the arduino and the Xbox 360 RF board (needs 3.3v) connected to 1 USB cable or will this cause problems?

Does that change anything Robert Peter Oakes

Clem

Is this similar to what you are looking for?

https://dilisilib.wordpress.com/hacking/xbox-360-rf-module-arduino/

Is this similar to what you are looking for?

https://dilisilib.wordpress.com/hacking/xbox-360-rf-module-arduino/

yes thats exactly what i am on about. i was going to post that but you beat me to it.

Ok. What you could do is adapt the diagram on that page, and wire it up in a similar approach to this:

Again, ignore the greyed out parts. Put the 5V of your USB cable to the 5V on the Arduino. Connect the 3.3v terminal to your Xbox RF module, and link the GND of the Arduino to the USB GND.

wont i need any diode on the 3.3v on the one to the RF module to prevent the current going back into the 3.3v line? the RF module is bi-directional or something

A fly back diode would be a safe bet.

whats a flyback diode? ive never heard of one or seen one before.

http://en.wikipedia.org/wiki/Flyback_diode

Google is your friend.

That is the name of the function the diode does in

wont i need any diode on the 3.3v on the one to the RF module to prevent the current going back into the 3.3v line? the RF module is bi-directional or something

so what type of flyback diode would i need or is there only 1 type?

If the USB is the only source of power in your circuit then there won't be any reverse current on the 3.3V line from the Arduino to the Xbox 360 RF board.  In the original circuit, the guy was using two diodes to drop the 5V to near 3.3V (3.6V assuming 0.7V drop across each diode).

However, as Robert Peter Oakes said, you'll most likely need to convert the 5V I/O voltage to 3.3V using one of the methods he listed. That is assuming that the Xbox 360 RF board is using 3.3V logic and not regulating down to 2.5V or 1.8V, etc..

so even though the RF module can sent the flow of current back to the arduino, its not going to damage it?. the reason for the diodes is to bring it to 3.3v but also to prevent the voltage drop that would burn out the RF module and the USB controller.