Ok, here's the idea:
You need to design a system that can count how many elements there are in a certain streak. Say, for example, your streak is based on 0-9 digits (as opposed to a-b-c-d-e-f). The challenge is then to make a machine that, feeding from a random generator, counts how many times in a row the random generator spits out a 0-9 digit. For example, if the "randomer" spits out an E followed by 2,4,6,1,9,0,5,D, the machine should be able to recognize that you had a streak of 7 numbers in a row. Also, if the machine hits a letter after a streak of numbers, the "elements in the streak" counter should return to 0.
Of course, you don't have to just consider a streak for numbers 0-9. You could make a machine that counts streaks of odd numbers, or letters, or 0s and 1s, or whatever. Also, this is not required, but if would be cool if the machine would, after finishing reading a streak, spit out a crate with the number of how many elements were in that streak.