i'm doing some researches about how to close/open RS485 data line in my RS485 multi device bus.
I'm following this nice research-document: Link Here.
Basically i'm thinking how to solve this problem in a real-world environment, as you can see in page 43, the strategy is very simple: every slave, using a microcontroller and a relay, will have A-B data lines normally closed, and when the master want to set/reset/reconfigure the slaves address it will manage the relay coil and sends to the respective slave the "configuration" messages.
I wish to receive some advices in how i can manage the RS485 data lines using a low cost and effective solution without using a relay: my goal is to develop the same system using smd components.
I have 10 contact sensors that are placed around my home, they monitor the door open/close status and using RS485 trancievers the slaves (that are equipped with an ATMEGA328P) will expose those information to the master of the bus. Now, i want to be free to position those devices in my home without worrying to set a slave address hardcoded in my firmware or using hardware dip-switches.
They are connected using a CAT5e cable and the total length is around 20 meters, the cable will transport: A-B-VCC-GND.
Every device is wired in daisy chain mode and the preceding device will control the power up of the following sensor, using a mosfet on GND controlled by the MCU (as reported in the image below):
I don't know if that can really work: the RS485 data lines are connected anyway, also if the circuit is not powered on...
Basically, this "sequential power up" is intended to solve the issue to know "where (for example) is located the device with id 3?"