I will have perhaps up to 50 sensors - my design. Each sensor will have a PIC to control the sensor and handle communication. The maximum distance between the sensors and the data receiver will be three metres and should use as few wires as possible.

What would be the best communication method for such a system?

 

Bluetooth. 0 wires.

 

My usual sensor design tree.
If the sensors are critical (SPC logged data) to the process, hardwire it. If the sensors are for nice to have data (motor/bearing temps, etc ...) then wireless is OK.

 

Will 50 bluetooth transceivers happily co-exist? PICs don't do bluetooth so that is a lot of extra hardware and I have no experience of engineering bluetooth.

It is important that I do not lose any messages but some delay in receiving is OK.
I was expecting this would be a wired system. I thought of I2C but that would mean the master polling all receivers in turn which would work but doesn't seem very efficient. Would a multi-master system work, with each sensor being a master?

 

Will 50 bluetooth transceivers happily co-exist? PICs don't do bluetooth so that is a lot of extra hardware and I have no experience of engineering bluetooth.

It is important that I do not lose any messages but some delay in receiving is OK.
I was expecting this would be a wired system. I thought of I2C but that would mean the master polling all receivers in turn which would work but doesn't seem very efficient. Would a multi-master system work, with each sensor being a master?

For a wired system, what's needed depends on the data requirements of speed, payload, response time and error handling. I would likely go with CAN BUS today. There are CANBUS modules in PIC18 controllers that only need a bus transceiver for reliable industrial strength sensor networks with four wires (three if you don't need sensor power, twisted pair for data and ground)
https://www.microchip.com/en-us/pro...tion-connectivity-peripherals/can-peripherals
https://www.microchip.com/en-us/pro...microprocessors/8-bit-mcus/pic-mcus/pic18-q84

My CAN-FD experience with the Q84 series controllers has been very good.

 

What is the update rate from each sensor?
Are all sensors sending data at the same rate but at different time slots?
How much data will each sensor send?
Is it one-way communication, i.e. sensor -> receiver?

My standard communication for industrial applications would be 2-wire (plus ground) RS-485.
Another solution would be 1-wire (plus ground) daisy-chained shift registers.

 

As a follow up from my last post, I think 2-wire SPI would work nicely (DATA and CLOCK).
You daisy chain MOSI and MISO in a loop around all sensors and the receiver. You send as many clock pulses as required to get all data to be sent around the loop (and you don't have to close the loop after the receiver).

 

What is the bandwidth required?