Summary: Why can I upload sketches to a Mega 2560 board by itself, but not when it is connected to a robotic arm?
The 2560 is connected to a Mac and to power using a two-pronged USB cable. One prong goes into power, and the other into the Mac to upload code. The prongs join together into one cord and are connected to a printer cable, which is then plugged into the 2560.
When my robot arm is not plugged in to the board, I can successfully upload any sketch to the board. When I plug the arm in, select the port that has the Arduino tag, and click upload, I get the following errors:
avrdude: ser_open(): can't open device "/dev/cu.usbmodem861": No such file or directory ioctl("TIOCMGET"): Inappropriate ioctl for device ioctl("TIOCMGET"): Inappropriate ioctl for device avrdude: ser_send(): write error: Bad file descriptor avrdude: stk500_send(): failed to send command to serial port avrdude: stk500v2_ReceiveMessage(): timeout
... some more repetitions of "write error: bad file descriptor", "failed to send command", "timeout"...
avrdude: stk500v2_getsync(): timeout communicating with programmer avrdude done. Thank you. the selected serial port does not exist or your board is not connected
When I next click on the port button, the port number has changed. When I select the new port number and try to upload, I get the same errors and the port number changes again.
I have tried: restarting the IDE with the board plugged in, using a different USB port, different printer cable, and searching Google and various forums. One person suggested opening the sketch from the program list instead of by clicking on the .ino file. I don't know how to get to this program list, because when I click to launch the Arduino app, the sketch I am working on pops up. I was also advised to connect the negative outputs (grounds) of my power supplies together, but I am not sure how this works in the context of my USB powering (as opposed to connecting a power supply to the screw terminals on the shield.)
The only way to upload sketches that will work on the arm is to disconnect and re-connect the 12 wires that go from the board to the arm.
How can I upload programs to my board without disconnecting the arm every time I want to make a change? I'm a newbie to Arduino and would appreciate if anyone could point me in the right direction. Thanks for your help!
UPDATE: I am now powering the arm through the screw terminals instead of the y-usb cable. This has fixed the error.