Write my own OPC

Question 1

Can I write my own OPC server and OPC client for a PLC that want to send and receive real-time data to the server ??

yes you can, sounds as if you only need OPC DA i.e. read/write of values.

How much is easy for a undergraduate student ??!!

It depends, if you want to implement OPCDA 3.0 then you would need some knowledge about COM which could be daunting if you haven't worked with it before. Normally when you create a OPC server you would use a framework from some vendor e.g. Matrikon but if you are on a tight budget you may need to do it all yourself.

Or can I use free software for the server (for example "MartikonOPC Explorer") and for the client to connect to the PLC ??

You can use the Matrikon OPC explorer to connect to your OPC server but normally you want to embedd your client code in a program and do something with the values, the explorer is more for testing

Which Programming language can I use ?

For the server part C/C++, for the client part you are more flexible, any language that supports COM

Alternatively you could implement an OPC UA server instead, OPC UA is platform independent and pretty much language independent.

See more at opcfoundation.org

Question 2

Depending on your skills the answer can be yes or no. The OPC foundation holds the standards and these are available to members.

Keep in mind that PLC's don't use OPC for communication, an OPC server uses the PLC manufacturers propriety protocol to be able to "serve" data to clients using OPC protocol.

To properly answer this question it needs a lot of clarification, how much is easy for a undergraduate student depends on what you study.

Which programming language to use, any you can find, what's your prefference.

Question 3

Python is easy way and can do. Only create global communication module (global for reuse). Some problems :

1- More PLC brand use BUFFER for access (Delta not use).Need register first later can read (all EV values).

2-All inside a thread (not only one, per node threading)

3-Your resolution is 1/10 sec(for modbus over serial)

4-Need write a strong security program in PLC (otherwise claim a lot risk!)

5-Minimal communication line is 2(two)(when lose one, use other).

All programming language is a baby. If you feed a lot and love it, groove up faster.You can do ! Don't forget you got a baby!

Question 4

Last time I checked Delphi was the only one to have both free OPC client and OPC server examples. I have made both OPC DA 2.04 servers and clients using sources from this page.