24v COB rgb 840 strip controled by Raspberry Pi

I like the idea. of using an optocoupler between the MOSFET and the 24v strip. I think it will provide electrical isolation and prevent signal leakage between the Raspberry Pi and the LEDs. This will be an effective way to protect my Raspi from potential voltage spikes... Loke, when I plug in the power cord for the Strip... lol. This should minimize the risk of signal leakage.   Thanks 

 colporteur did you look at the 817's datasheet??

Please look at Fig  14. Notice the resistor (R_D )before the input? The board look like there is none. So refer to my response above and use the formula but change the 5v to 3v and away you go.. 

you can take a look at this article here opens new tab.

The board has the resistor R_D, indicated with red arrow. However, there is an additional LED in series (yellow arrow).

The board manufacturer saved $0.0001 by eliminating an additional resistor this way (they could have had the additional LED in parallel, with it's own separate additional resistor.

Some stuff is great. AliExpress is excellent for some non-critical things that would not be affordable otherwise. For sure some stuff needs to be avoided. Similarly, I cannot imagine not using PCB manufacturers in China, for non-critical prototypes. I decided to try prototype 3D printing last week. I've not received the items yet (so it could be a big [but low-cost] mistake! : ) I hope not) but for now it saved me having to buy and learn how to use a 3D printer.

In this case, I too agree this board is not great. The lack of clearance is worrying too, some people may try to use it with mains.

I believe it would also be cheaper in this case, to buy just the optocoupler parts and self-solder them either onto perfboard or a custom PCB.

My apologies  fskrzycki for my response on using modules solutions to solve problems consuming your post. That was never my intention. 

You being a new member, it does provide an example of the potential the E14 Community provides. You will need to develop the ability to keep from getting upset or offended by the things other people say and do. You have to have a thick skin when it comes to criticism. Most responses are OK but with 700K members there may be some responses that reflect a lack of emotional intelligence.

I remember one of my early forum adventures when I tried to help out a fellow member with my limited knowledge. I suggested a simple solution, and then this person got all fired up and replied, "Some of us solder components!"  My kids still crack up about that post. 

I look on in envy at some of the more advanced techniques members have talked about on the site. I'm happy to have moved from hand drawn PCB's etched in chemicals to KiCAD documents used to manufacture quality PCB's. The tax and duty kills me!

I think about doing SMD but for the small projects I attempt through-hole works. Call me old school, that is OK.

Many of careers involved defining requirements. It helps separate the I want from the I needs. Sometimes what you are required to do is not what you want to do. I do value the E14 Community as a knowledge resource. I get some confidence from tapping into others experience instead of going it alone.

i planned on making a custom PCB. Im i misunderstanding The GPIO layout on my Raspi 4b. i see pin 2&4 are 5v?

There is a link for that.

 Raspberry Pi 4 Model B Default GPIO Pinout with PoE Header