The following circuits show the original and the updated version of the input section of a break wire alarm. The sensor is a 20m long twisted wire 0.1mm, which activates the alarm when broken. The wire keeps the logic input low and when it opens the logic input goes high. The first priority in designing this circuit was maximum robustness against false alarm due to RFI and other induced noises, and also low power consumption as it's powered by a 9V battery. Although the protection seems to be enough I'd like your input regarding the value of chosen capacitors and whether they are all necessary. Additionally, other suggestions regarding the design of PCB will be welcomed.The PCB is a regular two layer type with copper plane assigned as the ground.
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