http://www.online-stopwatch.com/full-screen-interval-timer/?c=3y9pwsydb
The above link will take you to a simple timer that should work on smart phones and computers, enabling you to instantly have intervals set up for each workout. At the bottom right, you'll want to change "restart when done" to "on" as the default is off.
You'll have 68 seconds for the exercise, which is your PE or SE, and then 68 seconds for the mobility. The alarm goes off for 8 seconds, which gives you time to transition from your PE to your mobility and back.
Obviously you can adjust the interval times if you need to, but I have found this to be a very useful tool when working out in my home gym. I don't have a smart phone, but when I get one someday I'll probably use this for the gym as well.