user50343: I am working as an internship on an Arduino based PLC. It is the M-Duino 58 Analog from IndustrialShields. I try to figure out how it works; Reverse Engineering. But i dont know why it has negative Digital Inputs like normal Digital Input I1.0 also has a connection -I1.0.
It is probably a simple question but i cant figure it out. Hope you guys can help me.

I guess i figured it out. Seems to be the GND connections. Should read the Manual better next time.


user4143: It looks like those inputs are opto-isolated. That means that the "input" goes through a resistor and the internal LED of an opto-isolator, which then comes back out of the "-" pin:

simulate this circuit – Schematic created using CircuitLab
So "-" connects to the ground of the remote device, and the "input" connects to the signal.  

50343: <p>I am working as an internship on an Arduino based PLC. It is the M-Duino 58 Analog from IndustrialShields. I try to figure out how it works; Reverse Engineering. But i dont know why it has negative Digital Inputs like normal Digital Input I1.0 also has a connection -I1.0.
It is probably a simple question but i cant figure it out. Hope you guys can help me.</p>

<p><a href="https://i.stack.imgur.com/0NVZ0.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/0NVZ0.jpg" alt="enter image description here"></a></p>

<p>I guess i figured it out. Seems to be the GND connections. Should read the Manual better next time.</p>

<p><a href="https://i.stack.imgur.com/IV5W0.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/IV5W0.png" alt="enter image description here"></a></p>
 4143: <p>It looks like those inputs are opto-isolated. That means that the "input" goes through a resistor and the internal LED of an opto-isolator, which then comes back out of the "-" pin:</p>



<p><img src="https://i.stack.imgur.com/24D5A.png" alt="schematic"></p>



<p><sup><a href="/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2f24D5A.png">simulate this circuit</a> &ndash; Schematic created using <a href="https://www.circuitlab.com/" rel="nofollow">CircuitLab</a></sup></p>

<p>So "-" connects to the ground of the remote device, and the "input" connects to the signal.  </p>
