dencraw
Hi.
I was designing a PNP output to be fully compatible with  IEC-61131 but after a lot of thinking and trials i came up with a veteran chip (VNI4140K) in the PLC market, very cheap.
the output provide shortcut, over-voltage, over-current protection.
I have designed also a software output shutdown circuit.
the chip provide an open collector status output, so i collect all together to a single Arduino input, if there is any error the plc shutdown the outputs.
for my project i only need two inputs and 8 outputs,.. since Arduino uno is I/O limited i have implemented an analog keyboard that i have posted back in 2002 in the PIClist form MIT. here: http://www.piclist.com/techref/microchip/4x4key1ad7r.htm
Since i need only 5 keys, is easier to filter a huge range between resistors with a few lines of code:
sensorValue = analogRead(sensorPin);
sensorValue = sensorValue>>6;
sensorValue = sensorValue<<6;
perhaps someone can improve my ideas. At least i can relay now on a solid output hardware.
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thiagoralves
Nice diagram! Do you know any other ICs on the market, common to other PLCs, that are used on analog inputs as well? I'm thinking about putting together an "OpenPLC approved" industry-grade I/O circuitry that can be used by the community to ruggedize Arduinos and Pis
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dencraw
I know that are colleagues around working with Pt 100, etc... but is not my case. I never was in the need to use Analog I/O. there are some industrial characteristics that i hope it can be find in a single chip... also analog outputs with short-circuit protection etc.
If i find something for sure i ill test it first... best regards.
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dencraw


https://www.analog.com/media/en/analog-dialogue/volume-43/number-2/articles/simplified-design-of-industrial-process-control-systems.pdf
https://www.digikey.com/reference-designs/en/wired-communication/interface-solutions/1683
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thiagoralves
Nice finding. I’ll keep it on my list, although I think this design has too many ICs. I’m thinking about a simplistic and cheaper solution, maybe just using an op amp and a regular adc 
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