Apparatus for discriminating between objects

An apparatus for discriminating between a first surface type and a second surface wherein said first surface type reflectivity is higher than said second surface type reflectivity comprising:

• a light source for illuminate said first surface type or said second surface type;
• a photosensor for measuring the reflectivity of said first or second surface type;
• a first gain element for adjusting a voltage or current from said photosensor based on said measured reflectivity;
• a second gain element for adjusting a measurement of a current or a voltage supplied to said light source;
• a subtractor for subtracting the first adjusted voltage or current from the first gain element and the adjusted measurement from the second gain element to provide a subtractor output value;
• wherein said subtractor output value is close to zero with respect to said second surface type and said subtractor output value is near a maximum with respect to said first surface type;
• a threshold value generator for generating a threshold reference value;
• and
• a comparator which compares said adjusted reflection value and said threshold reference value and indicates whether said first surface type or said second surface type is present.