I've reviewed my electric lessons, but i have some difficulties understanding the schematic at http://sensor-networks.org/index.php?page=0820520514
It's said: "Finally, we have to connect the pin 6 in arduino with pin 9 in XBee, since Arduino is working with 5v and XBee with 3.3 V, we shouldn't connect them directly, we are going to use a resistor bridge to adapt these levels (see image)."
I really don't understand how sensor-networks has established that a resistor bridge with 10k and 15k resistors will do the trick
Voltage from arduino pin 6 (or 7) is a fix value (isn't it ?) 5V, and voltage for xbee pin 9 is a fix value (isn't it ?) 3.3V
But about current, what it is ? I thought it was 40mA from pin 7, but it's complete non sens: 5 V = 10k * 40mA + 3.3, it makes 5 V = 403.3 V, something wrong...
I've done a pastebin http://pastebin.com/m5be6d1e0 for naming current and voltage (I goes from up to down)
Spec for Xbee is at http://www.libelium.com/squidbee/upload/3/31/Data-sheet-max-stream.pdf and information on xbee sleep mode is at page 22 (section 2.5.3)
Any idea to how have been calculated those resistors is welcome...