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Components to put bw 3.3v signal and 5v

I have an Arm based platform with Serial UART interface but in 3.3v level.

I want it to communicate with my Arduino.

I have a 3.3v power source in the Arduino(Dumilinove).

My question is what components to put between the 3.3v platform RX/TX and the Arduino RX/TX ?

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I had the same problem interfacing Mr. Tidy (5V) with an Xbee module (3.3V). Here is the Schematic I posted then.

Xbee_interface_Schematic.jpg

In your case you can leave out the 3 diodes, 3K3 resistor and 10uF capacitor I used to create a 3.2V supply.

The schematic above will work with a PICAXE, but not with an Arduino. The PICAXE use inverted signals for RX/TX. You will need a second transistor stage on each side to inverted the signal once more for the ARM/Arduino. Or you can use the simpler sparkfun level converter schematic.
Good point, I forgot I had to invert the signal for Picaxe.