A digital frequency comparator includes two double-edge triggered flip-flops and a combination logic. The housing is provided for holding the ballot generated by the interactive user terminal. Color-staining problem between two neighboring inkpads is prevented and the base can freely extend to open and contract to close causing variant configurations and shapes. The communication system is configured to transmit the information to the monitoring station. The device also includes a crystallization-inhibitor incorporated within the electron-transporting layer, wherein the crystallization-inhibitor prevents the electron-transporting layer from crystallizing during operation, and a cathode disposed over the electron-transporting layer.