The scenario
Designing a circuit for linking two doors over long distance with RS-485, each door controller manages a lock relay and door sensor.
What is in this drawing
Read the decisions behind it.
01
Use MAX485 for RS-485 communication
02
Single microcontroller per door with relay driver
03
Fail-safe biasing and termination for RS-485
04
Door sensor with pull-up and switch to ground
Use this circuit as a reference for bidirectional door interlock systems in secure facilities with long cable runs.
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