555 TIMER : BISTABLE MODE: Close the top left switch and open it back. The TRIG pin gets grounded and the LED switches on AND stays on. It is in a stable ON mode. Close the switch to the right of the last one then open it back. This time the RES pin gets grounded, the LED goes AND stays off. It is in a stable OFF mode. The 2 pins mentionned here act as Flip-Flops. It is therefore called a bistable mode since both the ON and OFF modes are stable once trigered via the grounding of either the TRIG or RES pins.
