SoftwareSerial to 12V Serial

Hi all

I have a nagging problem that I just can't seem to solve. I have a standalone ATMega328P on a custom PCB that is bootloaded with Optiboot so I can use the Arduino IDE to program it thru a FT232RL. I'm now trying to get a Software Serial port to send some data back to me but I just can't get it working. The Software serial, from what I can see works. When I hook up an Oscilloscope to the TX pin, I can see it "talking" @ ~3.3V. In the end I will need to convert this to 12V serial levels, so another computer can receive data from it. I've read that the Max232 or Max3232 should do that, so I bought these:

However, no matter how I hook either of these to the TX Pin of the Software Serial, I just don't see any signal with the oscilloscope.

The first step goal will be to connect the software serial back to the PC using a serial to USB converter and seeing if the sent data is received correctly.

So my questions are now: Has anybody already done such a thing and can maybe provide a schema or something that shows how exactly this is done? I think I need a Max232CPE to do the conversion, is that correct? Since another PC needs to read data sent from the ATMega, would I be better off using e.g. a ATMega644 with 2 hardware serial ports? Or would software Serial be sufficient? (Transmittion rate is 9600baud and there are a couple of bytes to send every second.

Thanks a lot for any help on this, I'm starting to pull my hair with this problem. Martin

First a clarification. There is no 12 volt serial. There is RS-232, which is usually +- 3 to 12 volt or more. Your Max 3232 should work for you. Then there is the usual question: do you have the grounds all connected together?


Hi Paul

Thanks for your reply. Yes of course I meant RS-232 Serial. Thanks for the info on the Max3232, I'll give it another go and hopefully can get it to work. Yes, the grounds are connected together.

Cheers Martin