Follow-Along/Tracking Outdoor String Lights

Looking for feedback on this project approach.

Goal: Linear strand of overhead string lights (like these), that fade on (in front of) and off (behind) to light the path of the user.

Proposed Approach:

  • Wire WEMOS D1 Mini boards every 9 feet, with PIR sensor on each board.
  • Each board pings a centralized Raspberry Pi server every (X)ms with sensor state, and checks for brightness settings.
  • Server calculates the user's location based on received sensor states and responds with the appropriate brightness levels of the 2 lights that the board controls.
  • The board then runs a ramp script to adjust the 2 LEDs to those brightness settings using the PWM output from 2 of the digital pins.

Diagram

I want to do this over 200-300 feet of trail, so I am thinking to avoid voltage drop issues, I might provide 12V of power and put a voltage converter leading to each board so there's reliable 5V for the circuits.

I am curious if people have any thoughts on whether this will work, or suggestions for better chance of success before I order 20 boards and sensors, haha.

Thanks!

Almost any significant load at 12V is going to be a problem running 200-300 feet. Especially considering wire cost, as the heavier the guage, the more expensive. I think you need to solve power distribution before you even begin with the other stuff. Also that part of it will have to be weather resistant, along with the rest of it. To make the bulbs controllable, you would have to chop the 50 foot strings that you linked to.

Good point. Let's assume 200ft for now. I think I can solve the issue with:

  • Starting voltage of 24V
  • 2 strand 14 AWG wire running the length of the project (200ft)
  • A buck converter taking the variable voltage along the line and converting it to 5v for the individual boards (it seems common to have a 4.5 - 24V input range).
  • Wemos D1 Minis run at ~70mA while using WiFi, so 22 boards x 0.07A = 1.6A
  • Say we limit to 7 lights on at a time = 7 X 0.33A = 2.33A
  • Throw in 50% fudge factor = 4A * 1.5 = 6A
  • 200ft of 14AWG copper at 24V with a 6A load = ~6V voltage drop = 18V at last circuit.

This seems entirely manageable, and conservative since the calculations above assume the load is all at the end of the 200ft, rather than spaced out over the length.

And yes, I'd plan on chopping up a light string like the one I linked to and just use the waterproof sockets. The boards and such would probably just be heat-shrinked - this would be as a temporary art installation.

What voltage are the lights? The Amazon listing isn't a technical one.

Yeah, sorry, that listing is not very helpful. I believe they are 3V, 1W bulbs like these: https://www.amazon.com/Visther-S14-Replacement-Shatterproof-15-Pack/dp/B08Y8K7XW7

Yeah, better. Still, 3V is not a technical spec in that context. Do you know of any hacking of those bulbs (i.e. use in other than the supplied fixtures)? It talks about a "LED driver", makes me wonder what they really do...

Have you tried applying 3V to them? 5V? How would you translate your 5V to 3V if you need to do that?

Another possible "gotcha"... if they have internal voltage converters, will those work with PWM? If so, at what frequency? Not all their 120V "cousins" are "dimmable".

Great questions. I'll definitely order a few bulbs and experiment.

The Wemos D1 Mini boards are based around the ESP8266, which outputs 3.3V on the digital pins, so I'm not worried about the voltage for the bulbs. The 5V is for the board's power supply.

That said, it would be a bummer if they had an internal voltage converter and did not respond to PWM dimming....I'd have to look elsewhere for a simpler bulb if that was the case.

Good idea. I'm not sure the ESP voltage is relevant, since the pins can't supply that much current. I would worry about wifi coverage at 300 feet. I suggest RS-485 instead.

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Hi,

I agree, as you are going to need to run power cable.
Or Canbus, both are designed for multi stations on the one comms bus.

Then you could use Pro-Mini controller with a DC-DC converter to maintain 5V or 3V3 supply.


Smaller footprint?

You could use more stations then.

I like this project, very innovative. :+1:
Would be interesting to see how it would respond to two people travelling in opposite directions.

Tom... :smiley: :+1: :coffee: :australia:

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Ohhh, I knew I was missing something....overcurrent for the pins. Thank you for catching that! :slight_smile:

I do not think wifi will be an issue, but thank you for calling that out. Just in case, I want to experiment with the ESP-MESH (or similar) ESP based mesh networking code. From what I read the per-hop-latency is in the 10-70ms range, which should be more than fast enough for what I am planning.

I did research implementing RS-485, but that seems to involve an extra interface chip/board (couldn't find any cheap boards with an integrated RS-485 chip...unless I'm missing something?).

With the Wemos (or NodeMCU) boards being so cheap, I think the mesh approach without the need for additional cables or breakouts is going to be potentially easier (final last words, haha).

To dim the lights, I see 3 options:

  1. First is to use the 3.3V pin on the Wemos that can handle 0.5A paired with a transistor to power and control a single light (light should pull 0.33A max). This would require a board per light, but they are cheap enough, this might be OK?

  2. Second would be experiment with using the 5V output from the power converters on the 3V light paired with a transistor. I have a feeling they will be OK at 5V, but I will test that out.

  3. Third (and what I would like to avoid) would be to run another drop down power converter from 5v to 3v for the lights, paired with a transistor to control PWM dimming.