Among many methods investigated in literature, radiochromic films (RCFs) are becoming increasingly used at the basis of novel dosimeters design due to the property to change the reflectance in function of the radiation absorbed (i.e., the dose). The typical dosimeter RCF-based is composed of a broadband light source illuminating the RCF and a spectrometer, pairing the transmitted (or reflected) light to the absorbed dose, turning out to be expensive and not portable. In this paper a novel RCF-based sensing system is investigated, composed by a narrow band LED irradiating the RCF, and a silicon photodiode collecting the transmitted light. The electronic part handles LED driving and the transduction of the optical signal into electrical, as well as the data processing. The proposed apparatus was subjected to a calibration with certified films, obtaining the voltage-to-dose calibration curve, resulting in a low-cost sensing system for real-time dose monitoring.