Figure shoes the bus station indicator circuit . The circuit consists of 555 monostable delay circuit , counters IC2, decoding display IC3, audio delay circuit and other components. Monostable delay circuit by the 555 and Rt, Ct , etc. , whose delay time td1 = 1.1RtCt. Preset counter IC2 to be reversible 4-bit binary counter CD4516. 4-16 for the 4-bit latch IC3 line decoder . Audio circuit by the music integrated circuit IC4 (KD9300) , and speakers and other components. When you press the switch AN , by the pulse delay IC1 output increased to counter IC2, IC2 to add 1 ( minus 1 ) count , the output of Q1 ~ Q4 into IC3 decoding , decoder output after the delay circuit via IC5 Feedback to the IC3, to control , to delay and show them some time td2 td2 = 1.1RACA. At the same time control the audio output circuit IC5 IC4 output audio signals to drive speakers sound signal . Each car into a station , according to an AN, then repeat the process to facilitate the passengers get on and off .