See the minimum eligibility criteria for diploma is having passed 10. So if you have passed 10 then you can take admission in the polytechnic by giving the polytechnic entrance provided you must have >60% marks in your 10th. So you can do polytechnic this way as well.

To know more about Diploma in Engineering you may visit the link below:

https://engineering.careers360.com/articles/diploma-in-engineering

I hope this helps.