[Xml1-wire-devel] hubs and door locks, OW isolation

[Bruce B. <bb...@sy...>]

At 00:55 1/19/2001 +0100, Jac Kersing wrote:
>On Thu, 18 Jan 2001, Bruce Boyes wrote:
>
>> Someone else raised the scenario of a vandal plugging in a OW enabled PC
>> into the blue dot reader, looking for DS2406s on all DS2409 branches, and
>> turning them on in hopes of activating the door strike. Or plugging 120 VAC
>> into the blue dot reader!
>
>The 2409 solved the problem of outside access to other parts of the
>one-wire net, but the 230VAC (for us europeans) issue is one that keeps
>bugging me. Over a year ago I tried to raise this issue on the one-wire
>list, but there was no response at all. Like no-one else cared.
>
>Would it be possible to use some cheap parts (almost like the 2409 but
>with some component in the ground connection too) to isolate the reader
>from the rest of the net? Or would it be like protecting a transistor with
>a fuse? (A transistor protected by a fast-acting fuse will protect the
>fuse by blowing first.)

You can't opto-isolate OW nodes from the net (CAN and ethernet can). All
you can opto-isolate is a DS2480 (and the whole OW net which it drives)
from the UART which connects to the DS2480, since at that point you do have
access to separate TX and RX signals to control the isolator. This is
because with a one-signal party line you can't build an opto-isolator which
isn't also a positive feedback latch. You need both a TX and RX signal at
each node (ala CAN and ethernet).

Maybe transformer coupling is possible, I haven't thought it through. Then
you would at least have galvanic isolation.

Bruce
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