You need to realize the following connections:

1) LED strips - Wemos D1

2) LED strips - power supply

3) PIR sensors - Wemos D1

4) PIR sensors - power supply

5) Wemos D1 - power supply

6) power supply - house power network

Preparation: I had two cat 5 Ethernet cables (

https://en.wikipedia.org/wiki/Category_5_cable) installed under the floor between the skirting boards of the staricase and the hot press by the carpenter and the electrician before the carpenter installed the wooden floor. One cable per side of the staircase, popping out from the tip of the skirting board on one end, and from a hole in the wall of the hot press on the other end. A cat 5 cable has 8 small cables in it, divided into 4 twisted pairs using 4 different color bases and 2 color patterns (solid color, or dashed line). Remove 8-10 cm of rubber from each end of each of the cat 5 cables, so to access the 4 twister pairs. Un-twist each pair, so to end up with 8 indipendent tiny cables. Remove about 1cm of plastic only from each tip of each tiny cable, at both ends of each of the two cat 5 cables. This step is quite time consuming and I recommend using a proper cable peeler to do it quickly. I used scissors.

For the connection listed as 1), I picked the 4-way connector (plus the two extra power cables) from the LED strip, and connected the green cable from the LED (the data cable) to one of the 8 tiny cables from the cat 5 cable. I chose the white-orange pins of the cat 5 cable for this.

For the connection listed as 2), I picked the 4-way connector (plus the two extra power cables) from the LED strip, and connected the red cable from the LED connector (the VCC cable) to *two* of the 8 tiny cables from the cat 5 cable, re-twisted together. I chose the blue and white-blue pins of the cat 5 cable for this. Also, I connected the white cable from the LED connector (the GROUND cable) to *two* of the 8 tiny cables from the cat 5 cable, re-twisted together. I chose the brown and the green pins of the cat 5 cable for this. Lastly, to bring even more current to the strip, I connected the extra white cable from outside the LED connector (the extra GROUND cable) to one of the tiny cables from the cat 5 cable (I chose the white-green pin of the cat 5 cable for this), and the extra red cable from outside the LED connector (the extra VCC cable) to one of the tiny cables from the cat 5 cable (I chose the white-brown pin of the cat 5 cable for this). The reason for powering the LED strip with 3 cables bringing the positive, and 3 bringing the ground, is to distribute the current over more pins, to avoid over-heating and to make sure enough current reaches the LEDs. This could have been achieved by running a thicker cable just for power, but then I would have needed to run too many separate cables (a thick one for power, a thick one for ground, one data cable for the LEDs, one data cable for the PIR sensors. I preferred to pay the electrician less and have only 1 cable per side installed :)

For the connection listed as 3), I connected the "out" pin of the PIR sensor to one of the tiny cables from the cat 5 cable (I chose the orange pin of the cat 5 cable for this).

For the connection listed as 4), I connected the "vcc" pin of the PIR sensor to the white-brown tiny cable of the cat 5 cable which was already connected to the red cable from the LED strip, and the "ground" pin of the PIR sensor to the white-green tiny cable of the cat 5 cable which was already connected to the white cable from the LED strip.

All the above connections could be made more tidy by using heat-shrinkable tubes. I'm not using them, as I plan to cover everything with a white MDF board placed on top of the aluminum profile, so to embed the profile into the skirting board. This will hide all the cables and will leave me access in case repairs or further developments are needed.

These first 4 connections were replicated exactly on the other side of the staircase, where the other PIR sensor is.

Note also that the blue cable from the LED connector is left without a connection, as that's the redundant data from the ws2813 strip.

To realize the other sides of the connections (i.e. in the hot press), I have:

a) twisted back together the blue, white-blue, and white-brown pins of the cat 5 cables and I have inserted the result into one of the three "+V" ports of the power supply.

b) twisted back together the green, white-green, and brown pins of the cat 5 cables and I have inserted the result into one of the three "COM" ports of the puwer supply.

a) and b) were replicated for the other cat 5 cable corresponding to the other side of the staircase. I have used another "+V" and "COM" port(s) of the power supply.

c) the two orange pins of the two cat 5 cables were insrted into pins 4 and 5 of the Wemos D1

d) the two white-orange pins of the two cat 5 cables were twisted back together and inserted into pin 1 of the Wemos D1. Now, if I had used a regular Arduino Uno with a wifi shield or external esp8266 module, I could have left the two strips independent, not twisting the two cables, and connecting the two pins to pins 1 and 2 of the Arduino. This way, I could have controlled the animation of the two sides of the stairs separately. I decided to simplify, though, and kept them joined. This is a limitation of the Wemos D1 R1, that can drive a Neopixel-compatible LED strip only from pin 1. I'm not sure if they fixed this into R2, that's possible, if you end up trying with an R2 let me know if this works.

For the connection listed as 5), I had many possible options (like using a spare usb power supply for a phone and using directly the microusb port in the Wemos D1), but, since I had the last (third) pair of +V and COM ports from my 40A power supply unused, I decided to connect the 5v pin of the Wemos to the +V port of the power supply, and the GND pin of the Wemos to the COM port of the power supply. Please note this bypasses the internal voltage regulator of the Wemos and will only work if the power supply has a pretty constant voltage, which was my case. If not, you risk to burn the Wemos D1. Note that in the picture you'll see a microusb cable connected to the Wemos D1. Well, it's not connected to anything on the other side, I just left it there for when I have to plug the Wemos to the laptop to program it. As you'll discover in the later step, I am programming the Wemos wirelessly OTA (Over The Air) now, so that cable can be removed for good.

For the connection listed as 6), the electrictian left a white cable plugged to a fused switch, carrying 220v, popping out from the wall. So all I had to do was to take some of the rubber out at the end of the white cable, remove about 1 cm of rubber from each of the three contacts, then connect the brown into the "L" port of the power supply, the blue into the "N" port, and the yellow-green into the "earth" port.

This was by far the most time consuming step, also because I didn't use the proper tools for peeling off the cable rubber, I just used some kitchen scissors. I have always done it that way so my error rate was only 3/35 (where 35 is 8 pins from each cat 5 cable and each end of them, plus the 3 pins from the house network cable), i.e. I only had to re-cut 3 pins in total out of 35 connections. However, you can do it probably faster with a proper cable stripper.