Modern cryptographic protocols require good entropy sources. Unfortunately, many networked devices lack subsystems dedicated to this task, being potentially susceptible to random number generator (RNG) attacks. Yet, most of these systems allow software upgrades and host communication ports, providing the option of a retrofit. This work illustrates how chaotic dynamics can be used to design a sub-10$ entropy source capable of an over 48kbit/s rate and offering multiple serial communication abilities. Operation is based on a standard microcontroller and exploits a loop built around one of its analog to digital converters (ADCs). The design offers self-testing features and enables an experimental validation of some recent results on the choice of the best state quantization function to employ when using chaotic maps as RNGs.