I am excited to share that in May 2015, I was asked by my professor to present my class project at the Verona Robotic Fair. My project was to link three PLCs and make them communicate through some buttons that I installed on an electronic board. I programmed the PLCs to give an electric signal in one of their physical outputs based on a command code that I gave them. The starting PLC received the electric signal and, depending on the button I told it to, communicated a certain code to the other two PLCs.
The Race Condition Problem I faced
One of the biggest challenges I faced was that the communication channel between all three PLCs was a single optic fiber. This meant that I had to manage the race condition to this resource to avoid the PLCs communicating at the same time and disrupting the communication.
I didn’t know yet the solution I gave to the problem was a well known solution used in Operating Systems.
I solved the race condition by creating an header that I attached to the body of the packet sent into the optic fiber. The header contained the identifier of the target PLC while the body contained the command code to understand. All the PLC’s were receiving the packets and analysing the header of the conversation but only the target PLC was able to open the body while the others were just ignoring the message
Here is a more detailed explanation of how my solution works:
- All of the PLCs are constantly listening for packets on the optic fiber.
- When a PLC receives a packet, it checks the header of the packet to see if it is the target PLC.
- If the PLC is the target PLC, it opens the body of the packet and processes the command code.
- If the PLC is not the target PLC, it ignores the packet.
This ensures that only the target PLC processes the command code and that only one PLC is communicating on the optic fiber at a time, which prevents race conditions.
Proud that my work has been showed to the general public 🙂
My professor was impressed with my project, which is why he asked me to present it at the fair. I was honored to have the opportunity to present my work, and I enjoyed sharing my project with others.
I believe that my project is an achievement to be proud of. It uses something similar to an internet communication protocol to solve a problem I faced in the real world, and I didn’t know it was similar to that when I made it.
I am grateful to my professors for the opportunity to work on this project and to present it at the Verona Robotic Fair. It was a great learning experience!
DiegoTurri.com 
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