practice1

代码说明：

  工程教育中级练习题1：按一下K1键，LED以10Hz频率闪烁，屏幕上画出红圈，跟着闪，放开后保持该频率闪烁；长按K1键超过3秒，LED以5Hz频率闪烁，屏幕上画出红圈，跟着闪，放开后保持该频率闪烁；按一下K2键，LED熄灭；按一下K2键，LED常亮。(Secondary Exercise Question 1 in Engineering Education: Press the K1 key, the LED flickers at 10Hz frequency, draw a red circle on the screen, follow the flash, and keep the frequency flickering after release; Press the K1 key for more than 3 seconds, the LED flickers at 5Hz frequency, draw a red circle on the screen, follow the flash, and keep the frequency flickering after release; Press the K2 key, the LED goes out; Press the K2 key, the LED always shines.)