i have been playing with mbed since few week ago and would like to create a test program for dcmotor speed control. im using a 24V dc motor with encoder attach.. then test, at first i test with supplying a 5v and 3.3V from mbed to the motor. the thing work fine giving a 16 and 10rpm respectively. later i try using 12v it give 40rpm. then i try a 24v input, now the speed wont come out. and also the counter that count each on/off tick not counting up.
any possible reason? my though that maybe when it move so fast that the ISR routine couldn't catch up to the speed..