In this article, measurement of contact potential difference (CPD) between two dissimilar metals or alloys has been investigated by an actuating capacitor attached to a low cost home-made Kelvin probe system. The detailed sensing mechanism and analysis of the output signals for the CPD determination have been proposed. The resolution can reach 0.01 eV with three scientific digitals which is potentially used for the high-resolution measurement of non-contact mechanical, electrical properties and material science in a micro-domain phenomenon at low cost. A pure Ni probe was fabricated to measure the CPD of the electrodeposited Ni film and used as calibration data. The effect of Co atomic concentration on CPD of the electrodeposited Ni-Co alloys was studied for extending future application.