I'd like to second Gibbedy's request for reliable realtime software for graphing data sent over the Teensy USB serial connection. I have a Teensy project that has been sitting on the bench for months waiting for code to capture EEG data from the Teensy. A library (perhaps in c) that could be called from python would be a great solution, but I'm not sure what to look for or where to look. My only programming solution is max/msp, and it will not handle the baud rate that I need.
Paul, the Arduino serial plotter *does not* work reliably. When I saw your post, I tried it in Arduino 1.6.8. Closing the serial plotter screen occasionally and unpredictably causes disconnection of the USB port from the Teensy. The port completely vanishes and the port assignment must be reset to another one. After that, the plotter window is not visible (and cannot be found) and this error occurs when trying to use the serial monitor: "Serial monitor not available while plotter is open". So, neither the serial monitor nor the serial plotter are usable after this crash.
I finally recovered by running another Arduino sketch that uses the serial port. Next, I installed Arduino 1.6.9 and the recommended Teensy beta to see if this bug was fixed, but the problem was still present after the upgrade. In fact, the upgrade initialized with the problem still active -- the plotter window was inactive and the error message still present.
Best regards,
Michael