Which Bus?

[snx]

I have an application with a number of nodes (devices). These devices operate on batteries, but in the future they should be able to be connetec to a low voltage supply line (24VDC or similar). Since cables are necessary for this option, there would be also the possibility for a bus system that can revceive statistic parameters over a protocol.

My task is to find and evaluate a bus design. The given values are the following:

- There are around 100 Node devices per Master
- The nodes should be "anonymous" and plug and play, so no pairing etc. They just should "dump" their content on the bus and thats it
- The theoretical bus speed would be around 64bit/s, but in normal operation mode, the devices only send 64bits of data every 30-90minutes
- The bus message content is of pure statistical nature, so no critical information is transmitted, so a single message loss/corruption would not result in a problem. So it would be acceptable if some times 1% of the time the message would not get picked up
- The bus is only one way (node to master). A two way bus is also fine, but not required.


- If possible, it would be desired to connect the nodes via a "stub" to  some kind of a ring line, so that not every device would need a cable directly to the master, only to the next ring access point. The stub lenght would be around 2-4m. The complete ring/star lenght would be around 20-50m

- It would be a great benefit, if the bus would supply power (2 wires (data+power)) instead of 4 wires. I know that some intercom-systems use a two wire bus, that supply the devices and provide connection. In my case, every node needs 3.3v, 100mA, so consider 400mW per device (included reserve for voltage converter inefficiency, etc). The voltage on the bus can be any (up to 48V).

- The bus should be supported in the future (no end-of-life bus or legacy/hard to get parts)


What bus topology could be used fo this project? If there are any questions, feel free to ask

[helius]

Profibus sounds like an option: it supports something called MBP (Manchester bus-powered) that uses the same wires for power and data.

[rstofer]

At the bottom level, I would use RS485.  It is fast and it can go far.  Each node needs an input and output port and the entire network is one long string.  I used DIN connectors when I built up some nodes and I had an "IN" and "OUT" port on each node.  At the end of the line, I installed the terminating resistor in a DIN plug and plugged it in to the "OUT" port.  Easy!

https://www.maximintegrated.com/en/app-notes/index.mvp/id/763

Then I would need a protocol to ride over RS485 and I would be inclined to use ROBIN

http://www.bdmicro.com/code/robin/

This is a multi-master protocol with collision detection.  It can run as master-slave and not worry about collisions.

[rounin]

I like CAN Bus, 29bit address + 64bit data, very rugged. Would need separate power wires though, no combined power/data physical layer as far as I know.