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Recomended input protection circuits

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  • Recomended input protection circuits

    Has anyone got any known good input protection circuits - for the digital input and also the analogue circuit.
    I've removed the input resistor as mentioned in another thread.

    thanks.

  • #2
    affordable solution to I/O protection

    In ANY control environment that you want to be robust and tolerate "real world" transients (like static and lightning induced transients that are picked up by the sensor wiring) you should buffer any IO device (where possible) with opto-isolators and/or relays. I have used Industrologic's RIO8 to provide isolated relay outputs http://www.industrologic.com/rio8prod.htm and their UOB8 to buffer the digital inputs http://www.industrologic.com/uob8prod.htm If you need to isolate all the sensor grounds, their UOB4 has 4 completely separate isolators so there is no interaction with real-world grounds. http://www.industrologic.com/uobprod.htm These are top-notch quality products and frankly, you couldn't build them (time and materials) for the little money they charge for them. Buffering the analog inputs presents a bit of a challenge. Still working on that one....

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    • #3
      thanks for the tip.

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      • #4
        Analog Input Protection for ADIO

        I opto-isolated the ADIO digital inputs with the Industrologic 8 input opto boards. I also added a input conditioning circuit to ignore transients shorter than 1/4 second. This keeps lightning transients or spikes from heavy appliances cycling from false triggering Homeseer. The analog inputs present more of a challenge, so I have purchased some Burr-Brown ISO124P isolator chips to test http://www.ti.com/lit/ds/sbos074c/sbos074c.pdf Pretty neat device. You can put a +/-10V DC signal on the input and get an identical DC voltage on the output with NO GALVANIC CONNECTION between the input and output. Protects up to a 2kV differential. I plan to use these chips to isolate and protect the ADIO A/D converter inputs.

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        • #5
          That looks interesting. I was going to try to make a voltage follower with an op-amp, but so far i'm still running the guantlet with feeding sensors direct into the inputs.

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