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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.
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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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Hah! I would never have thought about using a 7805 for that purpose..... Nice!Originally Posted by Joe S.
I will never forget this one, hehehe
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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.
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How would a 7805 be a problem? I would think it would actually clean the signal with a cap or two.
Dave
Always wear safety glasses while programming.
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It will clean up one a bit, but PLC's are typically used in the most notoriously dirty environments, from an electrical standpoint. It may work for many applications (i.e. a quick & dirty fix), but an opto-iso is a better choice.
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Hi, I think a 7805 could be a solution for the output from the PLC to the PIC, but what about the output from the PIC to the PLC?
I still prefer the optocoupler solution for both sides.
Alfredo
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The cap is even worse. It can hold the input signal in a given state and cause false sensor readings. When it comes to PLCs, do it right and use optos for input and either optos or solid state relays for the outputs. The last thing you want is to go through the programming over and over trying to figure out why your timings are wrong.
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If you're looking for an "off the shelf" solution (which most of us are not) look at opto22 modules or similar.
Wisdom is knowing what path to take next... Integrity is taking it.
Ryan Miller
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