There are many entrance examinations to join BTech.Some of the top National level entrance exams are

Exam.             Commencement.        Exam Date

                         of Applications

JEE Main.       3rd week of Nov.        1st week of

                                                                    April

JEE Adv.        1st week of May.   Last week may

BITSAT          3rd week of Feb.    2nd week May 

VITEEE.         1st week of Dec  1st week of April

MUOET       last week of Oct.  2nd week of April

SRMEEE.     2nd week of Nov.  2nd week of Apr

There are also state level entrance examinations conducted for admission into colleges of that state.

There are also some colleges and universities which conduct entrance examinations for admission.

Minimum qualifying marks for some examinations are fixed but cutoff's for some exams depend on the total availability of seats,no. of students qualified,difficulty level of question paper.

All these institutions offer a wide range of courses.

For more details go through https://engineering.careers360.com/exams

All the best!!