Schematic diagram of timing alarm circuit based on MCS-51 single chip microcomputer
MCS-51 series AT89S51 single-chip microcomputer is selected as the microcontroller, and two quadruple common cathode digital tubes are selected to form an 8-bit display module. Due to the limited driving capability of AT89S51 single-chip microcomputer, two 74HC244 bus drives are used, and one 74HC244 completes the bit control line. The control and drive, the other 74HC244 completes the 7-segment output of the digital tube, and a 100 ohm resistor in series with each other on the output port limits the 7-segment digital tube.
Since the number of keyboards is small, the free-standing button is selected to be connected to the P1 port as four button inputs. P1.0-P1.3 is high when no key is pressed. When a key is pressed, the corresponding pin of P1.0-P1.3 is low. The circuit schematic is shown below.
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