WLED Animated Staircase Wipe

LED Strip

The most common strip beginners use for LED strip projects when starting out is the ubiquitous 5v WS2812B addressable LED strip. However, after doing some reading it was not what I landed on for this project in the end. Skip to the end of the section if you don’t care about the details.

The WS2812B is 5v, or 5 volts for you non-nerds. This is a pretty common hobby electronics voltage, and is very safe to work with - it’s almost impossible to give yourself a shock at 5v. USB power banks and chargers are all 5v, so it’s easy to find power supplies for them (ignoring the current requirements). The trouble is, 5v is almost too safe.

To run the length of my stairs, I would need a strip around 5m long. They make 5m strips in a range of voltages, so that is no problem, HOWEVER, the 5v strip does have one big limitation.

Voltage drop.

To put it simply, the voltage carried by the strip drops due to resistance in the wires that make it up and because of the 5v nature of the strip, the voltage at one end is noticeably lower than the other. The lower voltage causes the LED colors at the end of the strip to fade towards red compared to the start of the strip, which looks a bit bad when you can see the entire strip at once.

The other problem is that you need a beefier power supply to power the strip. Since power = voltage * current, for a given wattage at 5v, the current required is higher than at 12v or 24v. This isn’t a problem per se, but it means you need to use thicker cables to carry the power or you may have issues with the wires heating up, which worst case could cause a fire if you aren’t careful.

There are various ways around this problem, but they involved a fair bit more wiring for this length of strip, as well as increasing the size of the power supply needed. So rather than mess around with all that, it is simpler to get a higher voltage strip. Since the voltage is higher, there is a smaller drop due to the resistance, and fewer wires needed. This ofc presents a different problem for powering the controller, but more on that later.

After doing some research on various strips from the fantastic Quinled website, I decided on a 24v strip, which I think is a SK6812 COB strip. Using 24v means that I could use thinner wires to power the strip, and I wouldn’t have to worry about voltage drop as much. The only other downside was that the pixels on this strip are grouped into bundles of 3, so you lose a little bit of resolution. This wasn’t a problem for me, but something to be aware of.

Microcontroller

There are 2 main choices for microcontrollers that are commonly used with WLED - the ESP8266 and the ESP32. The ESP8266 is the older version of the ESPs, and is a little less powerful and has less memory. When comparing the prices on AliExpress, they were both pretty similar, around 6 bucks. So it made sense to just opt for the 32. They both take 5V power inputs, with the only difference being which GPIO pins are used for data.

Power

Because the strip is 24v, we need a 24v power supply. You can get these in a range of different current outputs so you need to pick one that should provide enough current for the LED strip you want to power. Different strips draw different amounts of power depending on their length and how many LEDs are actually on at a given time. Quinled has a good article on calculating how much power a given strip will need. I went with a 3 amp one because that should be good enough to power the strip at 100% white brightness.

There is an added complication with going for 24v of power however, in that the esp only takes 5v inputs. The 24v power supply would fry that poor little fella like a chicken wing if connected directly.

Thankfully there is an easy solve in the form of little electronic components called buck converters that can help with this. They take a higher voltage and convert it to a lower voltage. So we just need to find one that can convert 24v to 5v, and we are good to go.

I found one called the MP1584 that seemed like it would work. Going back to my philosophy of, ‘this stuff is pretty cheap, so try and (hopefully don’t) fry’, ¹ I went ahead and ordered it.

Relay

This is an optional component, but i’ll include it for completeness. The LED strips have a downside with their power usage in that when the strip is turned off in software, it is still actually on and consuming (a small amount of) power. I think it’s a fairly negligible amount, but we might as well try and do this properly while we’re here.

To fix this problem, we can use a relay. This is a small electromagnetic switch that allows you to toggle the power off via circuit. By connecting the power coming in to the LED strip through the relay, we can cut the power to the strip and reduce its draw down to zero. WLED even includes a handy relay control setting to do this automatically.

Motion sensors

There are 2 basic types of motion sensors that would work for what I wanted, passive infrared and time of flight sensors.

Passive Infrared (PIR) sensors are the most common type of motion sensor, and are what you would find in most home automation systems, or your standard home alarm system. They detect motion by sensing changes in infrared radiation, like the heat from a human body. They are cheap and easy to use, but they can be triggered by other heat sources, and have a wide detection area.

Time of flight (TOF) sensors are a little more advanced, and use a laser to detect motion through measuring how long it takes the beam to return a reading. They are more accurate and have a smaller detection area, but they are also more expensive and require more programming to use correctly.

Since I wanted to turn the lights on before someone reached the stairs, I opted for the PIR sensors to make use of their wider detection area. They are also cheaper and simpler to use, so it made sense.

Misc stuff

Wires, connectors, soldering iron, solder, heatshrink tubes, etc. I had most of this already, but I did need to get some connectors to connect the LED strip to the microcontroller. I went with JST connectors because they are small and easy to use.

For wires, I used 22 awg for data and low current connections, then 18 awg for the power connections to the LED strip. 18 awg is probably not strictly required, but I had it lying around.

I used a solderable breadboard to hold the ESP and connect everything to as it made it a little bit easier to work with. Not strictly required either.

Microcontroller

I started by attaching the ESP32 to header pins, placing that in the breadboard and soldering the connections in place. Jokes, I didn’t do that because i’m an idiot who loves pain. I soldered the esp directly to the breadboard, making it very impractical to remove later on. Don’t do this, use header pins - it will save you a lot of pain later on.

After soldering in the ESP, I connected a female barrel jack to two WAGO 3 way splitter connectors on the positive and negative wires. Using these is a bit nicer than soldering as they look much neater than a solder joint, and you get the added bonus of making them much easier to remove later on if you need to. From there, I connected another wire to the connector, then soldered it to the buck converter, matching positive to positive and negative to negative. I measured the output of the converter using a multimeter to tune it down to the correct level. The buck converter I am using has a tiny screw that allows you to set the output voltage, so I had to adjust this to be below 5v for the esp. The esp comes with its own built in voltage regulator, so anything between 5 and 3.3v should be fine. Once happy with the voltage, I could solder the output of the buck converter to the left power rails of the breadboard, then connect the rails to the gnd and vin pins on the esp32. Because the esp32 has 5v inputs on the left, and 3.3v outputs on the right, I stuck with this pattern for the breadboard power rails and designated the left side as 5v and the right side as 3.3v. This way, I could use the 5v for the LED strip and the 3.3v for the PIR sensors.

Turning on the power to check everything yielded no magic smoke, and the esp booted up.

LED strip

Next up, the LED strip itself.

Because our power rails on the breadboard are 5v (and because its a bad idea to run any serious current through the breadboard), we need to power the strip directly from the power supply instead of using the rails on the breadboard.

The WAGO connectors I chose have more than one output, so I could take another wire from each of the positive and negative terminals and attach them directly to the strip. Soldering the power lines direct to the strip works, then we just need to connect a data line from the esp to the strip.

Another thing to pay attention to is the direction of the strip. Digital LED strips work because each small segment forwards the data signal on to the next segment in the strip, but this only happens in one direction. So if you solder your data line to the back end of the strip, nothing will work. They will have an arrow printed on them telling you which way the data flows, so as long as you follow this arrow you will be sweet.

PIR sensors

The last piece of the puzzle. The sensors I found on AliExpress are very ideal for this kind of project; they accept a range of voltages, including 3.3v. In order to detect when someone is at the top OR the bottom of the stairs, we need 2 sensors. This means we need to solder 2 sets of leads to the 3.3v side of the breadboard, then 2 different data pins.

Once the power wires were in place, I used the multimeter to check the output by touching the negative probe to the 3.3v side negative rail on the breadboard, and the positive probe to the output pin of the sensor. Waving my hand in front of it produced a nice little voltage spike, so I could tell everything seemed to be working.

WLED

Once the sensors were in place, it was time to flash the code to the esp. This is pretty straightforward and I won’t cover it here since the WLED documentation is pretty good. Once installed, we just needed to set the GPIO pins to match what we had chosen for the LED data pin and the sensor pins.

With that in place, we could test everything properly. WLED has options for PIR sensors built it, so we can test both of the sensors individually. Happily, it all seemed to be working.