To make such a device the size of a penny (I'm going by the size of our (i.e., North American) pennies here), you're going to need to somehow design and manufacture an ASIC (application-specific integrated circuit). Now, this is certainly within the realm of possibility, but really only if you have a sizeable research and development budget, and you're looking at making thousands or tens of thousands of the things. Otherwise, this is not a feasible DIY project.