1-wire bus topology

  • Hi, I would like to connect 20 temperature sensors via 1-wire bus. Wiring to sensors is shielded STP with length from 4 to 25 meters in star topology.

    1. Do I need some expansion module (8channel 1Wire expander?) or is the Neuron 1-wire port sufficient?
    2. What's the limitation of cable length/number of sensors?
    3. Is somewhere described how your 2-wire topology works (I found only this http://unipi.technology/wiki/1Wire_topology) compared to classical 1-wire bus as shown here http://www.jon00.me.uk/images/1wirebus.gif.
    4. Why does the 1-wire Neuron connector has two DQ pins? Pin 6: Data (DQ) transmission, pin 7: Data (DQ) reception

  • administrators


    the 1Wire network is a great thing but it always depends on the environment of your application. It might even work on the table but wen put together along with the rest of the cables you might need to split it into multiple channels.

    So back to your questions:

    1. The 8channel 1Wire expander is not yet done for the Neuron but it is doable with the old exapnder but we do not provide any tutorials or guides. But we have a customer, that has about 20 temperature sensors on a single channel...
    2. As sated on the wiki and in this text...
    3. Everything is described on the wiki - only to get maximum reliability. There is no change in the bus itself.
    4. It's a little confusing in the documentation of Neuron, but it has only one data pin. The network is the same as the first generation of UniPi

  • Thanks for reply and clarification.

    1. I'll try it on one channel and I'll see
    2. The wiki states:

    ... we are not trying to connect as many 1Wire devices as possible but to have maximum reliability. To achieve this we are trying to minimize the length of DQ line between the end point and the 1Wire bus. So we are using not 1Wire but rather 2Wire topology.
    This means that at the end device you have to connect the DQ line to both 6 and 7 pins of the RJ45 connector in order not to split the topology.

    And that's what I don't understand.. How do you minimize the length of DQ line with 2-wire topology, how does the topology look like? What's the point of connecting booth pins 6 and 7 to DQ?

    1. Thanks for clarification

  • administrators

    We do not minimize the total length of the DQ line but we rather have a little longer (twice) total topology weight and minimize the distance of the stubs to achieve linear topology. So the length of the stub is about 1cm max.


  • OK, thanks for the answer, now it makes more sense :-)
    The link you sent explains a lot. Maybe you could add it to your wiki.
    So the key point is, that your hub is replacing star topology with linear topology, which should be better for 1-wire network.