It can be challenging to get motivated to keep on a consistent exercise routine. I find it much easier to get into the groove when there is something interesting to keep your mind active. Lior Elazary has developed a great Interactive Punching Bag which is based around an Arduino microcontroller system. The sensor is a great idea and could be made from a few things around the house (assuming you have some conductive foam laying around). If you have a secret room in your gym you could set a secret punch sequence to unlock the door!
“The sensors are built using aluminum foil and conductive foam (I learned this technique from the Robot Builder Bonanza. I have the first version of this book, but I hope they kept it in this version as well). Cut two rectangles of aluminum (the size of the sensor), and solder two connectors to this. The bag has 3 modes, which you select in the beginning (all lights go on, and you punch on the light to select the mode). For now the LEDs are placed one in the left top, right top, and sternum. “