I know there are a huge number of classroom timers out there but this seems so easy I thought I would share it.  Google as a classroom timer, you simply type Set timer in the search bar and you get a timer.  You set your time and then you can go whole screen, it is nice a big so it can be projected for the whole class.  What a great thing and so easy.  I love easy!  Again, a tip from Free Technology for Teachers.