该功能用于初始化SPI通信。 设置通信时钟。时钟信号由主机产生，从机不用配置。但主机的SPI时钟频率应该在从机允许的处理速度范围内。 ~ SPI_CLOCK_DIV4，4分频（默认配置）； ~ SPI_CLOCK_DIV8，8分频； ...

In this quick Arduino tutorial I will explain how you can control a relay using the Arduino Board, one 1K and one 10K resistors, 1 BC547 transistor, one 6V or 12V relay, one 1N4007 diode and a 12V fan ...

I just received my RC522 RFID reader and made this simple Arduino access control system that uses the reader, a buzzer for the alarm and a relay shield for the security system. The relay can be used ...