5V RS-232 COM Port to Arduino Connection

Hello All!

This is my first forum post in Arduino community and I hope soon I'll be helping to other also!

I encountered with a stuation and couldn't find an explanation so I'm here writing to forum. I have to make connection between Arduino Mega and PCM 3362 Single Board PC.

I can easily make connection with USB port but we need USB for other things. Therefore, I want to find out how to use RS-232 COM port of our device. Problem is, in the datasheet of this device, it says RS-232 output is 5V. (because only power supply to PC is 5V too) Can I directly connect TX and RX pins or do I need inverter etc? Below, you can see the screenshot of the datasheet:

Another question is, is it better to use USB port? As far as I know, TX and RX pins will be used in arduino, in both cases and reliability and speed is the same. (maximum baud rate?)

Yes, you can connect the device directly to the Tx and Rx pins of one of the serial ports on the Mega. Connect Tx to Rx and vice versa. I suggest you use series resistors of about 10K, especially if there is the possibility of the Arduino being powered but not the PCM, or vice versa.

Thank you for your reply. What about other pins on the PC? Shall I leave them floating or make shourtcuts to themselves as explained in the link, under “cables” section.

link: http://arduino.cc/en/Tutorial/ArduinoSoftwareRS232

And also, to protect expensive PC, I want to double check if connection below is true?

PC_RX - 10K - Arduino TX
PC_TX - 10K - Arduino RX

Yes, those connections are correct. The other pins on the PC may be used for flow control, depending on the software on the PC. You can probably leave them floating, but if that doesn't work, connect CTS to RTS, and connect DTR to DSR. Or, if you want to control the rate at which date is sent to/from the Arduino, you can connect them to Arduino I/O pins.

I want to find out how to use RS-232 COM port of our device.

If the comport is actually rs-232 instead of TTL, then you may need a signal inverter.