I’m going to be powering an stm32 and also an RTK via usb c so I’m looking for a 12v to 5v converter so I can plug into a tractor. This is not coming from a cigarette lighter but directly from the fuse box instead . I’m not sure how dirty the tractor’s output is but I assume pretty bad.
My question is should I go for something like this Buck Converter - 8-20V to 5V/3A or do I need to make a pcb using a TVS diode in front of a D24V50F5?
And I should be able to cut a usb a to usb c cable and connect the red and black to 5v and it’s safe right?
It’ll depend on just how noisy it is vs signal…the setpdown will work, but we sell Opto-Isolators specifically built for this sort of thing SparkFun Opto-isolator Breakout - SparkFun Electronics
Yes, connecting the usb wires by color should be fine (though note some usb-c peripherals…like Apple stuff… look for/require in-line resistors for usb-c to work properly)
Opto isolators still require a 5v in. I thought they are for dealing with logic across different voltages not powering the micro controller from a higher voltage.
Do you want a project or a solution?
I used some of these for a project recently, keeping it all good 'ol 5 volt USB really simplifies assumptions and expansion.
They are, I was assuming the Arduino was doing other stuff too 
You’d have to test to be sure but I’m thinking either of the options you’ve linked would work (or brow’s suggestion as well!)
could absolutely work but I’m just skeptical when something like this is so much cheaper than even the pololu. Like it’s impossible to know the quality of these no name amazon brands and if they are actually automotive safe. I’m just afraid of destroying the rtk.
That’s true of anything, the mobile environment is tough.
Another one I forgot I also use (it’s so seamless!) is the fuse adapter for the USB dashcam. You can configure threshold voltages to help protect the battery.