Design, implement and test a full digital instrument -- 2

Design and test a digital (Arduino based) output light sensor capable to adapt and erase the ambient light. You will prove its functionality by showing an output value of zero volts (or close) measured with respect to the signal ground when the sensor is exposed to an arbitrary constant light source i.e. ambient light. The design must then show a variable output when exposed to a generated fast frequency light source, in addition to the ambient light source. The frequency of the variable output must be proportional the frequency of the fast frequency light source in presence of ambient light (i.e. not in a dark room). In other words, you can see this system as a light source frequency discriminator; it must be able to discriminate between a pulsing light source and the ambient light, i.e. ambient light, is automatically erased.