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1 wire bus

Former Member

Hi Peeps,

 

I am about to embark on a 1 wire bus project using devices such as the Maxim DS18S20DS18S20+ temperature sensor and other similar devices. The idea of the 1 wire bus seems groovy enough but I wondered if anyone out there had any experience of this stuff.

 

The concept of the project is in 2 major parts, the physical hardware implementation of devices connected ono the 1 wire bus along with a USB transciever to connect it into the main motherboard. The second part is the software which will be Linux based and the idea is to use the Linux DBUS mechanism to create a self describing (a method called introspection) platform for applications which are interested to get hold of sensor data. There is actually a 3rd parrt to this project which is the applications themselves, but before I go blabbing on in detail about the project I thought I ought to see if anyone has any comments to make first.

 

Fire away

  • I used Dallas one wire about 8 years ago and my memories of it are not pleasant! On a well laid out PCB the system works fine but if you intend running it over a cable network it can be less than impressive. It is susceptable to electrical noise causing devices to seem to disapear and then reapear for no imediatly obvious reason. After tearing my hair out for several months I left that company and swore never to use One-wire again. A few months later a tech freind of mine told a very similar war story and agrees that other than on a PCB it is a complete liability. In conclusion, if you want to run over a wired network DON'T TOUCH IT! Look at something boring like RS485

  • in reply to Former Member

    I think things must have improved since you had your mits on the 1 wire stuff. I've just banged together a prototype and strung 4 X DS18S20DS18S20+ digital thermometers on a 100M cable drum and they all report in no problem. Just for fun I shoved a GPRS modem into the middle of the coil while it was jabbering away to a mobile network and the 1 wire bus just kept on rollin in the data. I got some other 1 wire jobbies other than the thermometers to stick on it. I'll report back on how I get on with them once I get the USB drivers under control.

  • Hi

    I know that the discussion is old but feedback could be interresting for some other people
    I am using a 1 wire bus for my home automation (actually there is a temperature sensor in each room and 2 outdoor) 12 sensors DS18B20 in total. it's working fine.
    Next step will be with some DS2408 (8 I/O switch) for checking if windows and doors are opened or closed

  • Hi!

     

    Just wanted to give you info about my DS18B20 usage and experience. I'm using a DS2480B+DS2480B+ 1-wire driver to drive the network, ranging from 25 to 150 meter lengths thru a 16 channel mux and with 8-16 sensors per mux. The whole network is in total 2100 sensors spread over 20 pcbs with 16-channel muxes. It's more or less painless as long as you keep the total capacitance down on the network. Have the odd missed reading, but not many. They are all run on parasite power 24/7/365. A full scan takes 2520 seconds :-)

     

    I would not use these devices on a PCB to check local temperature, but for bigger networks I haven't really found anything competing with these buggers!

  • in reply to jrydmark

    Hi Johan

    Tks for you input...

    Can you tell me which kind of connectors, hub and cable you are using with your network?

    I try with RJ45 connectors and 3 way couplers, but i had some connexion issue.

  • Hello,

     

    I have a 1-wire network using 2 DS18B20's and an Embedded Data Systems HA7E 1-wire adapter in parasitic configuration. As the HA7E uses ASCII commands I use an Applescript to get the data from the sensors. The script basically polls one sensor then the other and writes the temps to a variable in my automation software.

     

    I've been having trouble with intermittent erroneous readings of 4095 a few times a day. I read that you need a 4.7k pull up resistor. I couldn't find a clear explanation of how to install it but from what I read it goes between 2 and pin 1/3 (they are soldered together for parasitic mode. I did the first sensor in the my network leg  and when I tried I got a constant 4095 reading from both sensors.

     

    Am I doing something wrong? I read on another site you need a diode to correct erroneous readings. I am a bit confused so if you can give me some advise I'd be most appreciative.