Connecting a 5.0V UART to a 3.3V UART

Hi!

I have a Microcontroller (Fujitsu MB90F347) running with 5.0V supply
voltage and a bluetooth module (Zeevo 3001Z) with 3.3V. Now I want to
connect them over UART.
Usually I would connect them directly. But this might not be possible
because of the different voltage levels.
Is there a simple solution how to do that? Perhaps I could convert the
signal twice using a MAX232 or similar. But as I wrote in a previous
thread, this somehow doesn't work. But I don't know why not. Any idea?

This brings me into serious trouble since I am not able to do further
work on this whole stuff and I have to match some deadlines. I am
really helpless because I just don't understand why this whole thing
doesn't work...

If anyone has an idea how to make communication possible, please help
me!
Thanks in advance,
Susanne Fischer

 

Hi!

I havent tried this, but it seems to make sense, it seems a simple
approach

The Fujitsu RX pin should be able to connect directly to the Zeevo 3v
TX pin, and get a clear signal.

The Zeevo RX pin should use a 2.5v zenner diode, to cut the incoming
5v signal down the that voltage.

One of them may be using 'inverted' comms, the other 'true'.

You can use a couple of transistors and a few resistors to make a
2-way inverter if necesary, i have done this before.

I dont think using 2 MAX232 chips would help if 1 of them is opposite.


Alex.