Read a lot of sensors in 100 meters cable

Hi all!

I’m involve in a project where I need to read sensors in a maximun distance of 100 meters. I have seen other posts and main posibilities are:

  • Consider using RS485 an arduino as master, and sensors plugged to an inexpensive microcontroller ATTiny to read the sensor, but I saw that RS485 has a limit of devices connected (32?) a need 100 or so. And it would be nice if I could plugged the sensor directly to RS485 but if the sensor should have a microcontroller inside or something

  • Consider other protocol?

  • Consider wireless communication, but to me that is not an option as I need to make it consumption efficient.

Do you think I am in the right direction using RS485? Do you know any other protocolo I could take into account?

Thank you very much in advance.

You could build some RS485 repeaters and use 3 buses of 32 devices each, end to end. Shorter strings would probably be easier to install anyway.

Thank you! I've seen as well that some protocols over RS485 allow to have more than 32 devices... as having 3 lines would force me to install an arduino mega with 4 serial lines, correct?

And talking about sensors... I guess I need a microcontroller per one or tow sensors I would like to read, correct?

if you look at RS485 as a platform and not a protocol.

you could put a ATTINY on each sensor to monitor the bus.
then read the first 32 sensors,
then send a signal to put all ATTINY's to sleep/standby
send a signal to wake up sensors 33 thru 64, read them.
then put all ATTINY's to sleep/standby
wake up 65 thru 94, read them
put all ATTINY's to sleep/standby...

I do not know if it has been done, or what would be involved.
and I suspect that it would be easier to use multiple busses.