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Circuit Of LED Digital Voice Timekeeping Clock

2017-01-07 14:52  
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Circuit Of LED Digital Voice Timekeeping Clock
General dynamics LED digital clock does not have the timekeeping function, but we only need to add a simple circuit to make it achieve the function of whole point timekeeping. This circuit has the programmable mute function, it will not alarm from 23:00 to 5:00. So it will not affect our sweety dream. The circuit is as shown. The signal of whole point timekeeping comes from the 8-pin of LED digital clock IC 3450 or 8560, this pin is the output-b-segment of the common cathode display. When the number is 0 to 4, b-segment is high level 1 , only when the number is 5, the level is 0 . So that when the time advanced from 59 minutes to 00 minutes, the potential changes from 0 to 1. This signal is limited by the resistor Rl, the 4N25 optocoupler will isolate coupling, transistor VT1 enlarge the signal and at last speaker BL will issue the chime sound.