To add to the article: both circuits are mere converters of a single analog input to PWM, which is not the best way to drive DC motors.<p>A good driver would also take the current consumed by the motor into account and adjust the duty cycle based on that to compensate for the slowdown due to the mechanical load and the coil resistance. Basically, a PWM driver that also emulates negative output resistance. If a motor has a known coil resistance, it is possible to achieve this both with a 555 (especially since there is also an unused op amp) and with a microcontroller.<p>And here is where a microcontroller with good software would shine and a 555 would not be capable of doing this:<p>* Adapting to unknown DC motors<p>* Tracking the motor speed not based on the estimated EMF (i.e., not on the voltage applied minus the estimated resistive drop in the coil), but on the periodic variations of the consumed current due to the changes of the relative orientation of the coils and the permanent magnets, i.e., using the motor itself as a crude angular position sensor