Noob here (APC220 )

based on this project http://arduino.cc/forum/index.php/topic,1357.0.html

in this part "On PC side, APC220 is communicating with Windows on serial COM port, so we can use Arduino's software as serial platform. As we are not talking to Arduino on this software this time, change of serial port is needed. In "Tools" -> "Serial Ports", select the COM port used by the APC220(the one with USB adapter connected to PC). Then click "Serial Monitor", type "A" and send, signal will be sent from PC to Arduino through the APC220 modules."

I got this problem " serial port 'COM7' already in use ".

how to solve this? anyone expert can help

That link refers to using RF-ANET to recognise and test the connection to the APC220. Have you done that?

yes I already done that part but using RF-Magic not RF-ANET , it use COM7 port.

Only one program can have the COM7 port open at a time. After you have successfully tested it with RF-Magic, you need to close RF-Magic to release the port before you can open the port using the Arduino serial monitor. (If that still doesn't work, double check that you have used exactly the same port in both cases.)

I presume you already fixed your problem, but if not, check the frequencies of the modules. RC_Magic defaulted to 470 when I initialized the modules. I could not communicate either way and finally discovered that 470 is outside the range. I re-adjusted to 434 and now have communication from the Arduino PC but still nothing from PC to Arduino.