We have two 3.3v systems communicating over RS232 protocol, but without any signal conditioning between them. One system has a regulated 3.3v connection to the automotive 12v supply (therefore infinite current source and steady voltage after regulation), the other is a battery driven device where the charge on the battery starts at 3.3v and drops over time.
We connected these two signals without an interface (not bright I know), and the regulator blew on the automotive side and damaged other components, I think because the battery side was lower than 3.3v.
Can anyone recommend a solution for connecting these two signals please? We had a similiar interface for I2C in which used a 2N7002DW Mosfet, but it seemed to affect the I2C signals in an adverse way because we could never get the I2C to work properly. When we removed an patched around the level interface and ran this on two systems with the same power source the I2C worked correctly. We never determined why this did not work and it was right out of the Philips appnote...maybe it was delays or rise times?
We thought we could use a 7407 OC but then we would have several inputs unused; so I was hoping that someone could recommend a best practice solution they have used. As usual cost is a factor. Thanks in advance for any suggestions.
