Good afternoon. I'm busy with a project interfacing a arduino pro (5v 328 version) with a Duemilanove. The pro sends one byte at a time to the Duemilanove, which in turn has to do a certain action when receiving it. Straightforward tx-rx rx-tx wiring.
The problem is that the pro version has two series resistors connected to the tx and rx pins. When i hook up the Duemilanove, it won't receive anything. When i manually bypass the resistors by holding the wire on the input side of the resistor, everything works as i was expecting.
Any suggestions on what to do, preferably other than replacing a very tiny smd resistor? I was thinking of putting pullup/pulldown resistors on the Duemilanove to +5V and GND, but im not sure about the values. Any suggestions?
I'm not convinced that these series resistors are the real issue here. My guess is that if you attempt serial communication between two pro's it would work ok (even though you then would have two times 1k series resistors).
The underlying issue is more likely that on the Duemillanove Rx/Tx is hardwired to the FTDI chip and anything wired to the same pins will conflict. The series resistor however causes the FTDI chip to win the race. Without one you may see the pro winning, but you may also destroy pins on either the Dumellianove, FTDI chip, PRO or all.
Possible solutions may be:
Use software serial on the Duemillanove (unused pins)
Use two-wire interface on both Arduino's (as opposed to HW-serial)
thanks for your proposed solution, i'll check what happens between two pro's. I do know that a boarduino to the Duemilanove will work. (This in fact is the same case as pro without resistor)
I need the Duemilanove for the wave shield attached to it, so ill try to let the pro send out a software serial signal and see what happens...