Prompt box with ok and cancel button

[steel5000]

I have made an animation of machine which speed up from 0 Rev/min to 3500 rev/min when I click START button. Now I would like to make a speed setter within this animation. The function of this speed setter would be like this, when I click on this speed setter button, a pop-up (small window) window with confirmation button will open where I can put the desire speed (which will be between 1 to 3500) and after pressing confirmation button the machine will gradually go to the set speed and loop at this speed. i.e: If I set 2000 rev/min then the machine speed gradually raise to 2000 Rev/Min and rotate at 2000 rev/min (after attaining set speed it should not be stopped. It should be rotating at set speed.)

Please help me. I will be grateful to you

Thanks and regards