We present in this paper a displacement-frequency sensor including a non-linear resistor with a dynatron-type i(v) dependence, a variable coil and a d.c. voltage source. A general relation is given for the dependence of the period of the oscillations on the coil inductance and on the negative variable resistance of the non-linear resistor respectively. The functioning data of the sensor are presented, for linear and angular displacement respectively. Our sensors could find interesting applications in cardiology.