  We present a simple low-cost electronic circuit that is able to show two
different dynamical regimens with oscillations of voltages and with constant
values of them. This device is designed as a negative feedback three-node
network inspired in the genetic repressilator. The circuit's behavior is
modeled by a system of differential equations which is studied in several
different ways by applying the dynamical system formalism, making numerical
simulations and constructing and measuring it experimentally. We find that the
most important characteristics of the Hopf bifurcation can be found and
controlled. Particularly, a resistor value plays the role of the bifurcation
parameter, which can be easily varied experimentally. As a result, this system
can be employed to introduce many aspects of a research in a real physical
system and it enables us to study one of the most important kinds of
bifurcation.
