practice for PID control

Dependencies:   PID QEI USBDevice mbed

Revision:
0:b2973a157cb6
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/USBDevice.lib	Tue Apr 15 02:02:38 2014 +0000
@@ -0,0 +1,1 @@
+http://mbed.org/users/mbed_official/code/USBDevice/#d495202c90f4