Staircase light circuit electronic
Switches S1 and S2 are definitely the two micro-switches, which give low inputs towards the respective de-bouncing circuits. Every de-bouncing circuit is constructed close to two NAND gates linked back to back. The de-bouncing circuits make sure a clean, bounce-free pulse at the output each time the micro-switch is pushed and released. The outputs from the two de-bouncing circuits are ORed working with diodes D1 and D2 (1N4001). So each time you push and release both of the micro-switches, you will get a positive-going pulse at the junction of the cathodes of diodes D1 and D2.
