1.In this circuit the R3, C1 and R6, C2 are said to act as low pass filters. The R3, C1 combo is easy to understand, however I don't get the R6, C2 configuration as they are parallel to each other, how can they act as a low pass filter? Also whats the function of D1?
2.The exit delay is achieved via C3,R7. The time constant RC determines the delay period, during which the gate input is held low. Does D2 act as some sort of protection?