Timing alarm circuit diagram based on AT89S51 single chip microcomputer

Single chip microcomputer STM32L151CCU6

Design a simple timing alarm controlled by a single chip microcomputer. It is required to count down according to the set initial value (1-59 seconds). When the timer reaches 0, the LED flashes “00” (flashing at 1Hz), and the button functions are as follows:

(1) Set button: In the countdown mode, press this button to stop the countdown and enter the setting state; if it is already in the setting state, this button is invalid. (2) Add one key: When setting the state, the number of the initial value increases by 1 each time the increment key is pressed. (3) One-key: When setting the state, each time the decrement key is pressed, the initial value is decremented by 1. (4) Confirmation key: In the setting state, after pressing this key, the MCU counts down according to the new initial value and displays the countdown number. This button has no effect if it is already in the timing state.