I have 2000 infrared proximity sensors along 100 meters, divided to 2 meter sections with an arduino reading them sending results by MAX485. For the power, I am supplying same 24v dc from each end of the line to prevent voltage drop, I don't have much space for a big wire, so I had to do that.
In every 2 meter section there is a small switching buck reducing voltage to 5 volts for arduino and other components including MAX485. This is a design for an industrial purpose where emf noise is present and the air is so humid and dusty, increasing the possibility of shorting on the PCB itself! I have already read other questions which were close to mine, but some points still not clear to me:
- In case of a short between 24v and 5v to the micro what will happen?! And how to prevent it?
- What about a short between 24v dc and rs485 data? How to prevent that? For the first point, even if it happens, in the worst situation I will lose my components on one section, but for the second one I guess all 50 sections are in danger.
I will use TVS diodes like SM712 which is really designed for transient and rs485 voltage levels, but I guess it can not help me for the short circuit. The 380v ac to 24v dc power supply has enough protection, and also a circuit breaker will be provided for the whole 24v line.
As I read in the same questions before, I will separate data and power cables, use earth connection, use different connectors for them, so the installation will be fool proof!