LockedI2C over Fiber Links

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2004/05/12 15:31:14 (permalink)
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I2C over Fiber Links

Is there any way to use I2C over dual fiber optic connections?
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    ric
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    RE: I2C over Fiber Links 2004/05/12 15:40:15 (permalink)
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    Technically, no. You could always put in some sort of intelligent buffer at each end of the fibre link.

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    RE: I2C over Fiber Links 2004/05/13 07:28:38 (permalink)
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    I'm looking at doing this for one of my projects, but probably not in a way that will be useful to you.
    The PIC will be inside an explosion-proof box close to a gas wellhead. It will be interfaced to multiple ADCs located just outside the box, in turn measuring the output of Hall effect sensors. The PIC will have to work at max speed to be able to measure the data fast enough. The data then has to be sent out to a safe area 50 metres away across the explosion-risk area. For a variety of reasons associated with size, weight and hazardous-area certification requirements it will be very expensive and maybe impossible to achieve the project target of data rate with conventional intrinsic-safety cabling and interfaces. So, my intended method is to buffer two fiber optic transmitters off the SDA and SCL lines, take the fibers through the Ex-box wall and away to the safe area where I will have to build a custom interface to decode the data. Should be fun.

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    ric
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    RE: I2C over Fiber Links 2004/05/13 14:26:19 (permalink)
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    So, my intended method is to buffer two fiber optic transmitters off the SDA and SCL lines, take the fibers through the Ex-box wall and away to the safe area where I will have to build a custom interface to decode the data. Should be fun.


    How are you going to get the ACK pulse back to the PIC?
    If you are running a transmit only interface, why not just run the USART at high speed?

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    RE: I2C over Fiber Links 2004/05/13 15:00:02 (permalink)
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    How are you going to get the ACK pulse back to the PIC?
    If you are running a transmit only interface, why not just run the USART at high speed?


    It will be transmit only.
    The problem is related to the severe restrictions placed on power and circuit impedances when operating in a hazardous area using Intrinsic Safety protection. Australia has its own standards for this, but similar to Europe and Canada. Its a long story, but the only copper-based digital interface I could use is limited to 31.25kbit/s and I need around 100k.

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    ric
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    RE: I2C over Fiber Links 2004/05/13 15:08:32 (permalink)
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    So run asynch at about 250k over a single IR link. Much easier. I2C is just not designed to go over other media.

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    RE: I2C over Fiber Links 2004/05/13 15:19:32 (permalink)
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    True, ric, that could work too. Bear in mind though that the transmission distance is 50 meters outdoor all-weather so fiber is still called for. I agree it makes sense to have the USART do the data encoding rather than build a custom receiver at the other end.

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    ric
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    RE: I2C over Fiber Links 2004/05/13 15:27:13 (permalink)
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    I meant fibre when I said "IR" :)

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    RE: I2C over Fiber Links 2004/05/13 22:37:05 (permalink)
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    Hi,
    I just want to second Richard about using the UART. I've used the old PIC16C74 to send and receive DMX streams (exactly 250kbps) on some projects and everything is OK.
    Regards,
    Vito.
    #9
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