A timer is a device that oscillates at an exact ...Source : <a href="http://ume.gatech.edu/mechatronics_course/Timer_F04.pptSlide">http://ume.gatech.edu/mechatronics_course/Timer_F04.pptSlide</a> 1 PPTPresentation Summary : 555 Timer Monostable Operation Monostable Operation ??? (one-shot) External capacitor is initially held discharged by transistor inside timer.