Arduino Pro Micro USB Macro Keyboard - Powering LEDs

Hello everyone! Following on from this thread - https://forum.arduino.cc/index.php?topic=686010.0 - I've got a pretty good idea as to what this person was trying to do, as I'm trying the same. Let's see if I can explain it a little better.

Building on from https://www.thingiverse.com/thing:4186055, as the previous poster mentioned, there is no guidance on adding LEDs to the mechanical switches. I've desoldered a handful of switches out of a Kingston HyperX Alloy keyboard (was scrapped, keys still work), and each key has a red LED included.

I'm a little confused at this point, as I can follow the guide easily enough like most, I'm not sure how to wire the LED's, in series, purely to power. Nothing fancy. Just when the macro box is connected to USB, the LED's are one. There's the usual 2 legs, nothing else involved. Plugged in=all LED's on.

This is where I've gotten lost. Where would I solder the wire running from LED to LED? Would I need to throw a resister in line?

Appreciate any guidance and help. Whilst it's easy enough to build this without the LED's, it would add a nice flair to the end result.

You need to figure what you are going to power them with. a 12V DC power supply would work OK. Next what color are they, that will give you a hint as to what the forward voltage drop is. You need to determine how bright you want them, probably 5mA would be a lot but I am guessing. Once you know this you would then wire them in series and parallel the series strings with a current limiting resistor in each string. Example, Assume the LED has a forward Vf (voltage drop) of 2 volts. You can take 5 of them (5 *2 = 10) leaving 2 volts. Then calculate the resistance you need to limit your current to 5 mA through the resistor. In a series circuit the current is the same in each leg. There are calculators online to do the calculations for you. Then add the current up for each string, that is the minimum current the power supply must give you. An additional 10 or 20 percent will only help.

Thanks gilshultz. Gives a bit more of an idea as to what I've got to work out. It's the same LEDs from the keyboard that was salvaged, as mentioned in the OP, red in colour.

As for a 12VDC power supply, I was hoping to find a way to power these through the Arduino Pro Micro along with the switches, so as to only have the single USB cable running the box.