Raspberry Pi Forums

I use one of those 5inch LCD's. The problem is I want to use this small fan I bought separately, but I can only connect it to the GPIO pins the LCD screen is already using. So how do I go about doing this? (please note I'm ultra noob and know nothing about this gpio stuff, but willing to learn)

Do you want to control the fan (speed) or simply have it running?

Having it running would be enough for me.

I don't understand this part of the question.

but I can only connect it to the GPIO pins the LCD screen is already using.

Why only to those pins? Are the other GPIOs in use? Do you only have wires to those?
Without knowing the detail of your LCD connection I would say:
NO! You can't arbitrarily multiplex LCD signals with a fan switch.
Knowing the protocol and all conditions under which you LCD is controlled, it might be possible
to use some pins combined with a decoder/statemachine to switch a fan on or off.
However from your remark "I'm ultra noob" I would guess that is beyond your capabilities.

A fan can be switched on/off from ANY GPIO pin, but it will require an extra driver like an NPN transistor or FET.
I am just about to write a multi page article on "how to control a relay from a computer" after seeing
that question for the hundredths time.

Isn't there only two 5V pins? Both of them are used by the LCD. So I don't know where else to connect it to.

I think we would benefit from a bit more description what you want.
I now understand you only need 5V for a fan. Just power to run a fan, nothing more.
You do not need to switch it on, nor do you need to switch it off in software or with a physical switch.
But your GPIO connector is already in use.

Then you must make some sort of extra connection. Solder a wire on the 5V pins or use a sort of
GPIO splitter.

As to the technical background:
Just like a power plug in your house you can tap off a power supply, like 5V, as many times as you want.
Just like a power plug in your house, if you connect enough equipment, at some time, something will give up.
In your house a fuse blows (most likely), you wires melt (less likely and less desirable) or a socket catches fire (also less likely and less desirable).
On your Pi most likely it will stop working because the supply short-circuit protection kicks in or a fuse blows (these are self-resetting fuses) or
you might wonder why at random times your Pi behaves 'weird'.
Or you have a very cheap Chinese power supply which has no short circuit protection and more-or-less 'just gives up',
becomes hot and hopefully does not catch fire.

Alright, would soldering the two wires (power and ground) below the circuit board work? (while the LCD is connected on top of the board where the pins come out the most)

The schematics are online - i.e. the one from RPi3 https://www.raspberrypi.org/documentati ... EDUCED.pdf

Have a look at them to figure out if there are other options for soldering your wires too. In case of the RPi 3 I would opt for the test pads next to power in:

Jiehfeng wrote:Alright, would soldering the two wires (power and ground) below the circuit board work? (while the LCD is connected on top of the board where the pins come out the most)

Yes.
Although I would always disconnect everything I can, your question give me the distinct feeling you can't.
But even soldering whilst leaving the LCD on top will work.
Make sure to use anti static precautions.

Alright much thanks guys, gonna try it out and post my results later.

Jiehfeng wrote: ↑

Mon Jan 09, 2017 4:35 pm

Alright much thanks guys, gonna try it out and post my results later.

Hi, I was wondering what happened to your project. Did it work?