Long 1-wire bus

[Ioannis]

Thanks Henrik.

The network of sensors will be different in every case. The end user will have 1 up to 8 max of these sensors.

They are connected in mixed ways, some with stubs of short length, others directly on the cable. I insisted on seperate line for the power and not use a parasitic power. After all, a UTP cable can support that.

At short distances it works just fine. Longer cables have some times error in the communication and lowering the pull-up, sure helps a lot.

I have read that article by Analog about active pull-ups. The problem, for me, is to write a routine that will do all of the signal handling, plus the 1-wire protocol, since OWIN and OWOUT do not support such a circuit.

Ioannis

[HenrikOlsson]

How do you distribute the power and signal across the pairs in the UTP-cable?
I mean, do you have one pair for power & ground and then a single wire for the data and if so, what do you do with the other wire of that pair?

I'd probably start with it grounded but I don't KNOW that's the best way.
Perhaps using BOTH wires in a pair for the signal?
Or run power and signal in one pair and both wires in another pair for ground.
Maby a capacitor across power and ground at the far end of the cable?
If the error(s) doesn't occur TOO often perhaps a simple retry is enough?

Just tossing ideas up in the air, perhaps one or more helps, I don't know :-)

I understand the "trickyness" in making this rugged if the bus topology is to be decided by the end user. I think you need to specify like max 50m length, each sensor connected to the main trunk by max 50cm - or whatever. Set that up with margin and test.