PLC Interfacing with PIC

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  1. - 5th June 2008, 06:32 #1
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    Default PLC Interfacing with PIC

    Hi all,

    This is my first post. Thanks in advance for helping me out.

    I am a user of both PLC (Ladder diagram) and PIC (PIC Basic PRO) using Keyence, IDEC PLC 24VDC and PIC16F877A. I am working on a machine process display project that monitors the process of a machine and displays the current process and errors using an LCD display. I plan to use PIC16F877A to monitor the inputs and outputs of my PLC, process the signals and display the current process at the LCD display.

    By doing that, I need to tap the 24VDC signals from PLC into PIC 5VDC. The problem is how can I convert 24VDC signal into 5VDC ? I am researching on optocouplers and zener diodes. Is there any simple and effective way of doing that? Any ideas are much appreciated.
  2. - 5th June 2008, 10:32 #2
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    You sound like your on the right track with the optos. I have made a few projects involving PLCs but I always interfaced to them using RS485 but I guess yours doesn't have that option.

    You shouldn't have a problem using optos to interface to the 24VDC but I don't think you need any diodes just the optos and some matching resisters but I could be wrong.
  3. - 5th June 2008, 17:13 #3
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    Hello skian85 and Welcome,
    The opto's are a good way, a perhaps simpler and cheaper way is to use a 78L05, regulator.They are in a TO92 package 3 wires.
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  4. - 5th June 2008, 18:32 #4
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    Quote Originally Posted by Joe S. View Post
    Hello skian85 and Welcome,
    The opto's are a good way, a perhaps simpler and cheaper way is to use a 78L05, regulator.They are in a TO92 package 3 wires.
    Hah! I would never have thought about using a 7805 for that purpose..... Nice!
    I will never forget this one, hehehe
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  5. - 5th June 2008, 20:56 #5
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    Quote Originally Posted by locko View Post
    Hah! I would never have thought about using a 7805 for that purpose..... Nice!
    I will never forget this one, hehehe
    It's cute, but with a PLC, I would go with the opto isolators. PLC's often switch relays and other noisy things in noisy environments, so you are probably much better off making sure you get a clean signal to your PIC.
  6. - 5th June 2008, 23:53 #6
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    Quote Originally Posted by tenaja View Post
    It's cute, but with a PLC, I would go with the opto isolators. PLC's often switch relays and other noisy things in noisy environments, so you are probably much better off making sure you get a clean signal to your PIC.
    How would a 7805 be a problem? I would think it would actually clean the signal with a cap or two.
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