Hi all.. I have a PLC system that is currently reading two digital input signals, one from a Limit Switch and the second one from a proximity sensor (with power). My goal is to use a Arduino microcontroller (2 DIs) to tap into those two signals, while PLC is doing its job without interrupted by Arduino. Can I just simply connect arduino in parallel with the PLC ?What do I need to pay attention using this configuration,
such as voltage or current drop ?
Do I need optocoupler or "transistor as a switch" to ensure no interference between PLC and arduino ?
most PLC's I have encountered run at higher voltages than the arduino, so direct connection would make a wonderful smoke generator (ie 24 volt signal going into a 5 volt digital pin)
if it were a 5v setup since both sides are high impedance there should be no problem connecting them in parallel as long as your grounds are connected. your biggest issue is how to take a higher voltage system and drop it down to 5v without too much current loss, so that your PLC doesnt register the signal
most PLC's I have encountered run at higher voltages than the arduino, so direct connection would make a wonderful smoke generator (ie 24 volt signal going into a 5 volt digital pin)
Huh? That makes no sense. A PLC controls circuit relaysor transistors from CMOS type devices. All CMOS devices I have encountered are 2-5V. Do you have a PLC circuit diagram that describes this 24v serial communication? I have seen ladder logic setups that require a 12v pulse but like most micro-controllers, it was probably used for high voltage programming (set everything to factory).
most PLC's I have encountered run at higher voltages than the arduino, so direct connection would make a wonderful smoke generator (ie 24 volt signal going into a 5 volt digital pin)
Huh? That makes no sense. A PLC controls circuit relaysor transistors from CMOS type devices. All CMOS devices I have encountered are 2-5V. Do you have a PLC circuit diagram that describes this 24v serial communication? I have seen ladder logic setups that require a 12v pulse but like most micro-controllers, it was probably used for high voltage programming (set everything to factory).
He is not talking about a PLC's communication bus but rather it's field input and output loops. Typically one buys a PLC with the type of input and output boards required for the installation and these can work at various voltages (24vdc and 120vac are two common types used for industrial use). One needs to be very careful if attempting to read a PLC's field input channel with an arduino of an existing signal wired to a PLC input channel. It's probably possible to do it safely but not something for an inexperianced person or if all the detailed technical documentation is not avalible.
not talking about serial communication, talking about input and output of the PlC
Yeah, I totally read the OP and your comment backwards and upside down. I think I spent way too much time working with a difficult member. Sorry about that.