PIR sensor notes
In this project you'll be using an Adafruit PIR sensor (or similar), and are going to configure it with a slow sensitivity (so it stays triggered for longer, which will use less calls to Adafruit IO and therefore have less impact on your rate limit).
If you read through the PIR learn guide, specifically the section on testing, then you will see the sensor can be configured for retriggering, and the sensitivity and timing can be adjusted.
I found adjusting the timing (delay) potentiometer to about 1/3 of a rotation from the start (if you turn the potentiometer anti-clockwise you will reach the start point) gave me about 30 seconds on-time, which felt about right.
The time should be adjustable between about 2 seconds and 2 minutes.
It can be helpful to mark any dial or adjustable knob and the surrounding area with a permanent marker or other tool, showing the direction the dial originally faced, or in my case the preferred position.
The sensor supports two modes of re-triggering, selectable by changing the Jumper between High and Low modes (marked H/L on the silkscreen). Read more about this on the PIR learn guide linked above, but the choice is between firing on then off each time period that movement is detected, or continuing to fire until movement is not detected.
Experiment with this and see which you prefer. Personally I found the continuous signal to be less useful as I wanted to be sure to receive a new value when fresh movement had been detected. As a result I selected the L mode. If using H-mode then you may wish to change the component Return Interval from detecting "On_Change" to "Periodically" and select a time period of "Every 30 seconds".
The Air Horn
This project uses a very loud 12 Volt car horn, although any similar thing could be used. It's marketed as 300 decibel, but that's the usual Amazon listings exaggerating the product specification. The actual horn is labeled as 410 Hz 12 Volts with no decibel rating.
I found one on Amazon for $15 (12 Volt and uses 3.5 Amps of current). Make sure the air horn you purchase uses under 60 Watts of current.
Mounting the Horn will require a 3D-printed bracket, or drilling a hole in your mounting plate. I've modeled a quick 3D printable bracket with space for the bolt to sit floating above the mounting plate. Find it on the Downloads page.
For the filament, I chose to use an elastomer (synthetic rubber) called TPU (Thermoplastic polyurethane), in White from manufacturer EryOne. I wanted something to reduce the vibrations when the horn is activated, which rubber is very good at.
Printing should be relatively simple, following your intuition for your own printer needs, the model will print flat on its base or standing on its side. I also tried a brim which aids with stability and bed adhesion but requires post-processing (trimming after printing).
My printer likes 225 Celsius for TPU and a bed temperature of 60 celsius.
Now onto the shopping list! You will need to purchase one Loud Horn:
Or
Parts
In addition to the car horn listed above, you'll also want to pick up the following electronic components:
Any 12Volt power supply which can supply 4 Amps or above will work just fine.
Why not check your box of old power supplies for a suitably rated unit before ordering a new one!
It must be marked with the Center pin as Positive like shown in the image.
You could instead use a USB-C based power suppply, but finding a cheap one that can supply 4Amps at 12Volts is not easy, and then you'll need an adapter or breakout too (like our USB Type C Power Delivery Breakout).
You'll also want to think about how this project will be mounted and if it will be enclosed. There is no right answer, so have fun experimenting with new techniques!
If you want to copy this guide exactly, then you'll need some fixings and a cross-head (Phillips/Posi-drive) screwdriver.
I've chosen the Nylon machine screws and stand-offs that come in a useful storage case:
You will also need one of the new Swirly Stemma Grid mounting plates!
Checkout the learn guide for more details, along with some tips & tricks.
Or:
Or:
I found that I could fit the project onto a 5x5 grid if I used both sides (and relied on the edges of the plate and horn to form a natural stand), or just one side when using a 5x10 (still tight use of space) or 10x10 grid.
Keen-eyed readers will spot I didn't have a 5x10 grid available, so I prototyped on paper (outlining and cutting out each component). It was very helpful to appreciate where the fixings would be attached.
You may wish to try a larger mounting plate to give yourself more room to comfortably position the components.
You can also choose to swap the Metro-ESP32-S2 board for another WipperSnapper-supported board.
The FunHouse is a perfect alternative, which is designed for a more compact and breadboard-friendly PIR sensor, and includes built-in environmental sensors and buzzer! That would allow a low-volume buzzer if the person is in the room, or the air horn if they are away somewhere in the distance.
Swap the PIR sensor for the breadboard-friendly plug and play version if you choose the FunHouse board instead of the Metro.
You will also want a double-ended Stemma cable for the relay, and if you have one of the older PIR sensors (not the breadboard-friendly version) then instead of jumper wires you'll want a Stemma to Female Header cable.
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