Right now i am looking for a better way to communicate to our wired nodes in a project that we are working on.
Currently there is 1 main node that all other nodes talk to that in turn handles all data back to a single computer. The nodes talk to the main node via Full Duplex 485.
I can do 4 nodes this way by having 4 separate 485 drivers sharing the same serial port to provide information to the nodes via the RS-485…
Topology goes as follows:
computer ----> main Node--> rs-485 --> daughter node
|--> rs-485 --> daughter node
|--> rs-485 --> daughter node
|--> rs-485 --> daughter node
|--> rs-485 --> daughter node
|--> rs-485 --> daughter node
(there are up to 12 nodes at this time that i need to communicate with, but more will eventually be created)
the rs-485 on the main node shares the second serial port on the device that is being used (there are 2 serial ports the other is being sent to the computer).
If i put a 5th device on the port that is live the signal on the serial port at the atmel device gets pulled from ~4.2V to about 2.9-3V for a digital high signal not including any extra noise from the multiple cable runs.
The length of the cables vary from 60Ft to 200Ft.
each node has a dedicated cable run that is terminated at the end of the run.
What is a recommended way of doing the communication between a single main node to many daughter nodes and allowing the daughter nodes to talk to the main node, but not to one another.
Best Answer
Could you set your daughter nodes as network slaves? Using a Master-Slave protocol and setting the daughters as slaves, they will only respond if they have been queried.
If I am not mistaken, using a multi-drop network topology with only one termination (rather than a a dedicated-terminated cable for each node), should avoid the large voltage drop.