Long 1-wire bus

[Acetronics2]

Hi, Ioannis

Have a look to Maxim AN 148 and AN244 ...

Best regards
Alain

[Ioannis]

Henrik:

I use one pair for the +5V, two pairs as ground and one pair as ground and signal.

I cannot be very strict on the precise topology the user will make.

You are right about different setup on the cables. Maybe some other configuration work better. It would be best though that we have a specific one for all networks.

Alain:
I did read all these AN and datasheets. The main trick to have long cable is to replace the passive pull up with active one, but this needs to come up with a routine, maybe in assembly, to control all the necessary timing for the pull-upo/pull-down and the 1-wire communication. This cannot be done with the commands OWIN and OWOUT and I am not that good anymore in assembly as I used to be 30 years ago, when I started with PIC controllers.

Ioannis

[lappy1]

Hi Ioannis !

The longest line for a ds18b20 in my heating is about 35 meters.
The sensor line to my oven ( it is a small water-bearing oven which is in my living room ) is a Ymm 4x1.5mm² cable, because of the line resistance. Attempts with a network cable failed miserably for me.
I chose the smallest pullup resistance according to the data sheet. It is a 1k resistor.
My setup is working now for 4 years without any problems

[Ioannis]

I was testing with telephone 4 wire cable initially and then with CAT-5 UTP cable.

As I have 2 pairs (and a half..) for power and one wire out of 8 for data, I thought I am OK and never thought wire resistance would be a problem.

Thanks for your input. Will see if thicker cable is better.

Ioannis

[lappy1]

Do not underestimate the voltage drop over long lines.
Also you should not use the parasitic mode. ( 2 lines ) . This causes more problems than it is useful.

[Ioannis]

Usually one thinks that thin cables will not be a problem since the current is really low, but you are right. It is more than the current. It is also the capacitance along with the voltage drop that all together will contribute in the system fail.

Ioannis