The scheme of a device that should have a simple and reliable implementation and that, under simply verifiable conditions, should generate a true random binary sequence is defined. Some tricks are used to suppress bias and correlation so that the desired statistical properties are obtained without using any pseudorandom transformation. The proposed scheme is well represented by an analytic model that describes the system behaviour both under normal conditions and when different failures occur. Within the model, it is shown that the system is robust to changes in the circuit parameters. Furthermore, a test procedure can be defined to verify the correct operation of the generator without performing any statistical analysis of its output.