2 layers27.9 × 16.5 mm
2 layers61.4 × 65.5 mm
Skyalarm
juhapark21/skyalarmThe sky alarm from xkcd #2979
- Size
- 61.4 × 65.5 mm
- Copper layers
- 2
- Thickness
- 1.6 mm
- Parts
- 18
- Nets
- 29
- Pads
- 56
- Tracks, vias
- 38, 55
- Pours
- 1
- Routed
- Yes
- KiCad
- KiCad 10.0 (file 20260206)
- Created
- 31 Jul 2026
- Updated
- 10 Oct 2026
Overview
Skyalarm is an open-source printed circuit board by juhapark21, from the juhapark21/skyalarm repository on GitHub, published under the MIT licence. It is a 2-layer board of 61.4 × 65.5 mm with 18 parts on 29 nets, routed with 38 tracks and 55 vias.
Its parts include 3 capacitors, 3 ICs, 3 connectors, 2 resistors and 1 transistor. It belongs with the ESP32 and RISC-V boards of this library.
README
README.mdSky Alarm
The sky alarm from xkcd #2979! It tells you when cool space things are happening.
Why
I also wanted this device. There are alert apps and telegram groups and RSS feeds out there, but I wanted something not tied to my phone or computer. I also thought it would be fun to make a large physical device in the style of the original comic.
Features
- Siren turns on (sound and light) when a cool space thing is happening in your location
- Only alerts for phenomena observable with the naked eye
- Cool space things:
- Lunar eclipses
- Solar eclipses
- Supermoons
- ISS passes
- Configurable notification settings
Usage
- Strip a cable (USB-C to USB-C or USB-A to USB-C; if using the latter, strip the USB-C end).
- Locate the power and ground cables.
- Secure the power and ground cables to their corresponding screw terminals (labeled on the PCB).
- Get two lengths of wire. Connect one end of each wire to the battery terminals of the siren. (You may need to disassemble or drill into the casing to access this)
- Connect the remaining end of each wire to the siren screw terminals (labeled on the PCB).
- Put in separate batteries for the siren. Make sure the switch is turned ON.
- Plug in any USB-C to USB-C wall charger to the XIAO ESP32C3.
- Plug in the external power cable.
Specifications
- XIAO ESP32C3 microcontroller - edit firmware without any extra equipment
- MAX98357A - cheap and widely available amplifier
- Any toy siren ~5V with an on-off switch and batteries should work
- 61.4 x 65.5 mm PCB - casing can be made smaller with different parts without adjusting the board
- Runs on any wall power supply 1A-3A (suggested)
- bom can be found as bom.csv
Upcoming features
- Weather checks - no alerts if overcast
- Description page for details about alerted event
- Custom audio
- Switching from API calls to local calculations for more predictable events
- More cool space things!
Images
Credits
Inspiration from https://xkcd.com/2979/
Font from https://github.com/ipython/xkcd-font
Parts
18| Qty | Value | Footprint | References |
|---|---|---|---|
| 6 | LOGO | LOGO | G***, G***, G***, G***, G***, G*** |
| 1 | 100uF | JLCImport:KS107M025E07RR0VH2FP0 | C2 |
| 1 | 10kΩ | JLCImport:MF1_4W-10K_1_T52 | R2 |
| 1 | 10uF | JLCImport:KTD350B106K43A0T00 | C3 |
| 1 | 220uF | JLCImport:ERG25V220M6X11 | C4 |
| 1 | 470Ω | JLCImport:MF1_2WS-470_1_T52 | R1 |
| 1 | Amp header | JLCImport:Header-Male-2_54_1x1 | P1 |
| 1 | DOP150N03 | EasyEDA2KiCad:TO-220-3_L10.0-W4.5-P2.54-L-1 | Q2 |
| 1 | External power | JLCImport:WJ500V-5_08-2P-14-00A | P2 |
| 1 | Siren header | JLCImport:Header-Male-2_54_1x1 | P3 |
| 1 | Siren wires | JLCImport:DB301V-3_5-2P-GN | U3 |
| 1 | XIAO-ESP32-C3-DIP | XIAO:XIAO-ESP32C3-DIP | U1 |
| 1 | adafruit-MAX98357 | ProjectSpecific:adafruit-MAX98357 | U4 |
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Questions
How big is the Skyalarm PCB?
It measures 61.4 × 65.5 mm and has 2 copper layers, 1.6 mm thick.
What parts does the Skyalarm use?
18 parts. The full list of its parts is on this page, with links to each part's symbol and footprint where PCBKit's library has them.
Where can I download the Skyalarm KiCad files?
From the juhapark21/skyalarm repository on GitHub, at the commit this page was made from: the board is pcb/SkyAlarm.kicad_pcb and its schematic pcb/SkyAlarm.kicad_sch. PCBKit opens the board in the browser, with nothing to install.
Can I use the Skyalarm design in my own project?
Its repository publishes it under the MIT licence: you may reuse it on that licence's terms (keep the author's notice, and for a copyleft licence share your changes alike).