Arduino USB powering Arduino and 3.3v device

Hi. Im a newbie when it comes to this stuff but i recently bought an arduino and i was wondering if i could use the arduino cable and splice into it and connect the arduino using standard 5v then add a zener diode on another wire attatched to the 5v wire. Can i do this? I need a 3.3v power source and 5v for the arduino without using 2 usb cables. I know its probably the bad way of doing it. Im just curious to see if i can do it. Its the arduino uno.

Thanks

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0 clem57 over 10 years ago in reply to alexbee13

A fly back diode would be a safe bet.
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0 alexbee13 over 10 years ago in reply to clem57

whats a flyback diode? ive never heard of one or seen one before.
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0 gadget.iom over 10 years ago in reply to alexbee13

http://en.wikipedia.org/wiki/Flyback_diode
Google is your friend.
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0 clem57 over 10 years ago in reply to alexbee13

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
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0 alexbee13 over 10 years ago in reply to gadget.iom

so what type of flyback diode would i need or is there only 1 type?
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0 pettitda over 10 years ago in reply to alexbee13

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..
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0 alexbee13 over 10 years ago in reply to pettitda

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.
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0 chrisdracko over 10 years ago

if you only need power for the zener diode and rf modular why not connect it to a standalone power suppy?
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0 screamingtiger over 10 years ago

One thing being left out, the device you are powering. How much current will it draw? The 3.3 output o the arduino is rated for 50ma. If you need more I can see why you want to use the USB.

I don't recommend splicing into a USB cable, they aren't very easy to work with, all the shielding, the tiny wires etc. The approach suggested is the best IF you are within the current tolerances of the 3.3V output of the Arduino.
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