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+--- Thread: One-wire limits ? (/showthread.php?tid=702)
One-wire limits ? - JD1 - 2017-08-23
Has anyone run into limits of how many temperature sensors or how long a wire run they can have with one wire ?
Things are starting to get kind of flaky here with 5 or so sensors with maybe 50 feet of wire (guess).
I am using cat 5 wire and have maybe 6 (guess) one to two splitters in the system.
Not all sensors are consistently seen.
A related question, in the 1-wire tab, will selecting 'restart' enumerate the attached devices? I have seen inconsistent behaviour but am not sure if it's the sensor system or if I am not using OpenPlotter correctly.
Has anyone used a dedicated one-wire interface rather than the bit bang approach that the pi uses to get 1-wire data ? The dedicated one-wire interfaces are more sophisticated and allow for longer/bigger one wire setups.
RE: One-wire limits ? - JD1 - 2017-08-24
After a lot of soul and internet searching, I decided to spend a small fortune on a 'linkUSB' which plugs into a USB port and drives a one wire interface. Supposedly, it's active adaptation technology is far superior to the bit banging approach of the pi and I am hoping that I will be able to run a much longer loop.
The unfortunate part - it will no be supported under OpenPlotter's 1-wire tab. I will have to build my own interface to the signalK server (somehow)
On the bright side, at least in theory I should be able to support all the other one-wire goodies that are out there such as switches and more. It won't be pretty, everything will be hard coded as my coding knowledge is woefully inadequate for doing a fancy UI.
RE: One-wire limits ? - shipahoy - 2017-08-24
1-wire is originally designed to be used on short distances, e.g. chips on the same board.
It is owned by Maxim (Dallas), and here is their guideline for long lines:
https://www.maximintegrated.com/en/app-notes/index.mvp/id/148
You should be able to drive up to about 200 m total cable length using a simple resistor pull-up according to Maxim.
If you use a 4.7k pull-up resistor, try replacing it with a lower value, e.g. 3.3k, 2.2k, 1.5k or 1k, and see which one works best.