is it possible to control the Fan from GPIO?

Question

am a programmer with no hardware knowledge background and defently no physics background.
I have a RPi4B and bought a fan bundled with its heatsink.
I realized the fan is basic and has 2 female pins to the 5V and ground.
I want to control the fan depending on CPU temperature. am well aware it's impossible with a software solution only because the 5V is always on. the 5V pin is not a GPIO pin, and only GPIO pins can be controlled from software.
so additional hardware is needed!
I found many articles and posts here how to do this with the help of a 2N222 transistor and a resistor. (which I just ordered from aliexpress lol. alongside the soldering iron and wire)
I noticed the fan is very quiet on the 3V pin so I got the idea to control the watt output too while keeping always on the 5V pin!(just like the gears in your car)
can this be acheived from software only ?
or can I use two different resistors to the transistor (each resistor is connected to a different GPIO) and control which GPIO is on ?

Answer 1

Perhaps the easiest way to do this is to add the one-line dtoverlay=gpio-fan facility to your /boot/config.txt file. You will still need to add some hardware, but the transistor and resistor may be all the hardware required.

You can learn a bit about the Raspberry Pi's device tree, and the pre-packaged overlays in this document. Scroll down or search this file until you find the dtoverlay=gpio-fan section.

Define the dtoverlay parameters:

You'll need to make two decisions to set this up:

1. the GPIO pin to use, and
2. the temperature at which the fan will turn on

Assuming your choices are GPIO 23 and 50℃, your one-line overlay is this:

dtoverlay=gpio-fan,gpiopin=23,temp=50000

To "install" this overlay, open the file /boot/config.txt in your editor, and insert this dtoverlay line somewhere above the [pi4] section near the end of the file.

The components and interconnections required are shown in the following schematic:

^{simulate this circuit – Schematic created using CircuitLab}

Some notes re this schematic:

1. You may use either the 5V supply (shown), or the 3.3V supply.
2. The diode D1 (1N4148) is optional, but preferable, to limit "back EMF" when the fan is switched off.
3. See this page for a "translation" between GPIO numbers and physical pin numbers

reboot and test

The dtoverlay will take effect after the next reboot. When the CPU temperature reaches 50℃, the designated GPIO will go "HIGH", thereby turning the transistor Q1 "ON", and causing the fan to start. When the temperature falls to approx 45℃, the fan will be switched "OFF" again.

Let us know if you have further questions.

Answer 2

Your Question is rather confused, but the following may help (if I understand what you are trying to ask).

You can not power a fan from GPIO pins. It is possible to power from 5V or 3.3V pins, but this will run all the time.
NOTE powering a 5V fan from 3.3V is not recommended.

Fan control is about the simplest workable solution. I use this on my Pi4 and the fan rarely operates, and only activates if it is stressed.

It is possible to control speed (over a limited range) using PWM. The hardware remains the same, you need to program the PWM duty cycle to control speed.

NOTE your question about different resistors is a bad idea. Operating a transistor in linear mode dissipates excessive heat; you would need to use trial and error to find a resistor which works (as Hfe of transistors varies) and motors are unreliable at low voltage.