A heterogeneous architecture combines, within the same hardware, different kinds of processors, with the goal of delivering fast execution at lower energy budgets. Because energy is such an important parameter of the efficiency of these architectures, much effort has been put into the implementation of techniques to measure the power dissipated by programs that they run. Yet, a vast majority of publications reporting experimental results produced on heterogeneous architectures either resort to simulations or rely on hardware counters; physical measurements are rare. In this paper, we introduce an apparatus-hardware and software-that we have been using to measure energy consumption in Odroid-based big.LITTLE architectures running the Android execution environment. This infrastructure is affordable and reliable. To demonstrate its viability, we show how we can use it to build oracles, i.e., a map that assigns different parts of a program to the hardware configuration that minimizes its energy consumption.