STM32 Cortex or PLC for a project ?

[ElFatih535]

Hello

I am building an arm for my final project at college, I am 4th year electrical engineering student, specifically Automation and Robotics.
Now I am thinking about how to control it, I already have a STM32F429ZI board and a friend has a PLC (forgot the model), if not his I also found a used Mitsubishi AL2-24MR-D for 60$.
There are 5 DC motors,5 DC servo motors, currently 3 but probably 5 potentiometer later for tracking rotation/movement, RGB color sensor which communicates over I2C, IR receiver(digital output) for some kind of control didn't think of what kind yet. Needs to be constantly connected to PC for position input and other control, I used RealTerm before, don't know if I can make some kind of GUI program that uses it to send data or something similar.
I was also thinking about making it controllable via a gamepad through a pc maybe as this will remain in a primary school after i finish it, make it a bit more interesting for children and all that.

If i use the STM I think I will have enough inputs and outputs for the project, if I use the PLC I think I will also have to use the STM board or arduino boards for different parts like connection to PC,maybe take all potentiometer analog inputs and then send it all over UART or I2C to PLC.
I want to do it this way because I believe it would be a great learning experience for me especially for PLC programming as I didn't get a lot of experience in university.
IR receiver code I have already written for different project and the RGB sensor needs to stay for other reasons so I might aswell leave it in the final project.
I have the time to do this atm, I don't care if it takes 10 more or less days to finish.

What do you think, is this too much, is it even worth including the PLC in this, considering PLC programming is a big factor in my profession ?

Thanks

[Paul Moir]

I can't imagine how a PLC will fit into this project.  The only thing I can think of that would be impressive would be to have the STM talk to it and have it handle some more autonomous functions.  But if you went the communications route it would take a lot longer and I think you would be looking for a different PLC.

If I were you, I would do the project with the STM especially if you are comfortable with that.  Do another, simple project on your own time with the PLC just exercising your use of timers, counters and maybe try a little math if the PLC is capable of it.  That would be *very* impressive to a potential employer as it shows you are willing and capable of learning diverse things on your own.  Eg, potential interview question "Why did you do this PLC project?"  Answer "I didn't feel my education sufficiently prepared me for programming PLCs and I thought PLC programming experience would be helpful in industry, so I did it to educate myself."  That would be an instant hire in my book.

[Doctorandus_P]

Euhm, both?

If you do a search on Ali / Ebay / China for "FX2N" you get lots of PLC boards starting at around EUR15.
A lot of these boards are built around a STM32F103.
There are lots of variants:
* Number of I/O.
* Relay or Transistor outputs.
* Different connectors (Do not buy the cheapest boards, these have bad connectors).
* Bare PCB, or housing with DIN rail mount.

I bought one of these just for fun and it looks reasonably well made. It's got a decent power supply with common mode choke, big caps and SMPS circuit.
Apparently these boards come pre-loaded with some (ripped off?) PLC firmware, but they also tend to have pads for a normal programming connector. I have a big dislike for PLC software, but very much like the STM32.

The biggest fault on the board I could see is that the RS485 interface is built with the quite fragile and obsolete SN75176 and there is no protection whatsoever on the RS485 wires. So if you want to use RS485, then add at least some TVS diodes to protect the SN75176, and preferably 100mA PPTC's to protect the TVS diodes from DC voltages. (This Idea is from Mike Harrison, (Mike's Electric Stuff)).