His test circuit uses six 2N2222 transistors to protect the Arduino from excessive current. You can see six red LEDs above which are inline with the base of teach transistor.

In our case fanSpeed will have a value of 32 at tempMin and 255 at tempMax. These values are used to control the speed of the fan using PWM and the analogWrite(). The fanLCD re-maps the temp to allow ...

His test circuit uses six 2N2222 transistors to protect the Arduino from excessive current. You can see six red LEDs above which are inline with the base of teach transistor.