FAN Detection Demo

1 Demo overview

This demo shows how to test the fan interface on the development board to start, stop, and adjust the speed of a fan.

2 FAN interface overview

The board's FAN interface is a 4-pin connector, but only three pins are active: 12V, PWM, and GND. The fan is controlled (start/stop and speed) via a PWM signal.

Open a terminal and copy the executable smdt_fan_demo from this demo's bin directory (05-Development Materials\Software Development Materials\linux_demo\smdt_fan_demo\bin) to the board's filesystem (the source code is available under the src path).

Optional: Because the board has a wireless network card, if the terminal keeps printing log messages generated by the wireless driver, you can change the Linux kernel log level with the following command.

#修改 Linux 内核日志的显示级别，内核的日志级别被设置为只显示紧急或更高级别的消息
echo 1 4 1 7 > /proc/sys/kernel/printk

First check whether the PWM device has been exported. If it has not, you need to export it. Here we choose the device pwmchip0 and export its first channel (pwm0).

#检查 /sys/class/pwm/pwmchip0 目录中是否有 pwm0
ls /sys/class/pwm/pwmchip0

#若没有，则导出 PWM 设备
echo 0 > /sys/class/pwm/pwmchip0/export

#再次检查是否成功导出 PWM 设备
ls /sys/class/pwm/pwmchip0

In the terminal, run the following commands to switch to the directory containing the smdt_fan_demo executable.

#切换到 smdt_fan_demo 可执行程序所在目录
cd ‘可执行文件所在目录’

#查看 smdt_fan_demo 是否在该目录下
ls

If the executable smdt_fan_demo is in the current directory, change its permissions.

#修改文件权限
chmod 777 smdt_fan_demo

#查询是否修改成功
ls -ld smdt_fan_demo

After confirming the permission change succeeded, run ./smdt_fan_demo -h to view the program's help information. Some default parameters set in this test script are as follows:

period: 200000, i.e. the PWM waveform period is 200ms.
polarity: normal — in this mode, duty_cycle represents the duration of the high level within one period.

#查看帮助信息
./smdt_fan_demo -h

The result is shown below:

Run the following commands to start, stop, and adjust the fan speed.

#查看帮助信息
#风扇启动
./smdt_fan_demo -s

#风扇调速
./smdt_fan_demo -p 50		#50%占空比

#风扇停止
./smdt_fan_demo -k

Fan start result:

Fan at 50% duty cycle result:

Fan stop result:

FAN Detection Demo

1 Demo overview

2 FAN interface overview

3 Procedure