Hi, I started doing a cardio / strength routine about six weeks ago with a resistance band that simulates rowing excercise - I needed to shake things up. Can't seem to find the link right now, but use a door attachment at about waist high, loop the band through it, and grip each handle standing far enough away that there is some tension in the band. Then with arms stretched forward, squat down, and as you stand back up pull both bands back towards the shoulders as on a rowing machine. Repeat. I do this for 30 seconds on and 30 seconds off. I like it because it provides a full body workout, and sometimes for variation I add push-ups or sit-ups during the intervals.
Here is an easy-to-use customizable online timer with a buzzer so you don't have to keep checking your watch. Free Workout Timer
I measure my calorie burn for all my workouts using a heart rate monitor, and here is a website where you can estimate your calorie burn using gender, age, and average heart rate. I use it for all my workouts... http://www.braydenwm.com/calburn.htm