DD-Exerciser.

So it took me ages to get around to this and I guess its the finished Beta - ready for testing by the no doubt chuffed recipient who wanted a clear box; this container was kicking its heels in the garage engorging bits and bobs that had no other home. 20 seconds exercise 10 seconds rest. Buzzer alarm. During human tests it was found to be accurate to 0.05 seconds and knackered me out on the 6th pass when on the heavy bag. It seems sitting may well be the new cancer - my active lifestyle has diminished by making this project which is joyfully hypocritical. I feel older and cleverer but not sure about wiser!

Thanks to all for the input on cascading timers. I'm off to get some fresh air but will return with the schematic.