Hi guys,

I am working on an addressable nursing call system using microcontrollers. I need a communication protocol that connects 100 slave nodes (rooms) to the master unit (nurse room) on a two wire communication. The distance is about 150 m. I want to make the power to the slave units on the same bus.

Any suggestions are welcomed.

Sherif Ahmed

 

Hello Ahmed;

This suggestion is based on an assupumtion that you will be using push-button units for the nurse call system; if you are thinking more of an interphone-voice system, then this cannot apply.

The distances and number of stations are slightly above the capacity of a single As-i network, but a combination of Profibus-DP or Ethernet and DP/As-i couplers would cover it well. As-i uses a profiled flat cable to connect individual digital signals to a PLC and provide 24 v power on a single bus.
Look at As-interface.com for details.

Hope this helps,
Daniel Chartier

 

Sherif,

Look at AS-interface. It combines power (up to 8 amps) and data on a single pair of wires. Segments are limited to 100 meters and 62 slave nodes, but most master units are available as dual masters so that you can have two segments. That's probably not a problem since nurse stations tend to be in the middle of the floor plan.

Turck (http://www.turck.com), for one, lists a variety of masters, power supplies, wiring devices and I/O (including OEM boards).

Mike

 

I know companies using CANopen for such systems.
Using 4 wires, two for communication, two for power - but it's one bus.

Heinz