Extra Screws, Issue 01: WiFi that senses, a wand that sleeps
Builds, hacks and the people making them.
In this bin: Opener / Builds / Shop Class / Datasheet Decoder / Bench
01Opener
WiFi that senses, a wand that sleeps
Three little ESP32 boards that learn how you move from WiFi alone. A wand whose battery math works out to about 1.8 years. A fountain pen you can print. Welcome to the first Extra Screws.
This one is for anyone with a project on the bench: a sensor rig, a printed gadget, a repaired radio, a face on a tiny screen. Each issue rounds up a few open projects worth a weekend. We link the original, credit the maker and note the license, so you know what you can borrow. When a project publishes a number worth knowing, we pass it on with the source.
Also in this bin: a lesson in battery math you can reuse on any sleepy build, and a radar chip that hides its antennas in the package.
02Builds
Builds worth a weekend
Three open projects, each with a real license file, and a note on why each one is worth your bench time.
3 × ESP32-S3 / 79.5% across 8 movements / WiFi CSI
WiFi Sensing Kit: three ESP32-S3s learn movement from WiFi alone
A webcam and an in-browser pose model label what you’re doing while three ESP32-S3 boards record WiFi channel state information. Then you cover the camera, and the WiFi model keeps guessing. The README reports 79.5% across 8 movements. The author’s own privacy note is worth keeping: WiFi sensing works through walls, so only point it at spaces and people who know about it.
The camera does the labeling for you, so you get a trained WiFi model without hand-tagging the data. That trick is worth borrowing for any sensor that’s hard to label.
Credit: andrisgauracs / License: MIT
github.com/andrisgauracs/wifi-sensing-kit →ESP32-S3 + 6-axis IMU / 25 µA standby / ESP-NOW
Muggles’ Wand: a TinyML gesture wand on an ESP32-S3
An ESP32-S3 and a 6-axis IMU inside a wand shell. Draw a shape in the air and it lights up, acts as a keyboard or mouse, or flips a light switch over ESP-NOW. Training tools are included, so you can retrain it on your own wave. Measured standby is 25 µA (more on that in Shop Class). The docs are in Chinese.
It’s a complete TinyML loop you can study end to end, from training tools to a working input device, with the power budget published part by part.
Credit: zou-shui / License: MIT (repo)
github.com/zou-shui/MugglesWand →One STL / Corn-cob ink feed / Open issues listed
White Feather wf672: a 3D-printed fountain pen
A one-STL fountain pen that borrows the grooved “corn cob” ink feed from classic WhiteFeather pens. Fair warning: the maker’s own latest report lists open problems, including an ink-leak path and tight seal tolerances. Follow along rather than expect a guaranteed weekend win.
The maker publishes what’s broken, not just what works. Those notes are a free lesson in tolerances for printed parts that have to seal.
Credit: Xarfa / License: CC BY 4.0
github.com/Xarfa/White-Feather-Fountain-Pen →Also on deck
e-paper-art-display. A Feather ESP32-C6 drives a big colour e-paper panel through a custom driver. It only uses power while the picture changes, which makes it a neat reference for any always-visible display.
FutureSharks / MIT / Source →
03Shop Class
Battery math: how a wand gets to 1.8 years on paper
Battery life for sleepy builds is simple division, if you count everything. The Muggles’ Wand README is a neat worked example: on paper its parts add up to 22.3 µA, and the measured standby is 25 µA. The ESP32-S3 is only 7 µA of that. The reset chip, fuel gauge, IMU and regulator make up the rest.
Steps
- Add up every part’s sleep current, including the easy-to-forget ones: reset supervisor, fuel gauge, regulator.
- Measure the real number with a meter or power profiler.
- Divide usable capacity, not the rated number, by average current. Here: 400 mAh ÷ 0.025 mA = 16,000 h, about 1.8 years.
- Sanity-check against self-discharge. The real figure will be shorter, as the author notes.
04Datasheet Decoder
TI IWR6843AOP: a radar chip with the antennas built in
Designing a 60 GHz antenna is the scary part of mmWave radar. This chip puts the antennas in the package, runs detection and tracking on board, and sends just the results to your microcontroller. Want to try one without laying out your own board? IWR-AOP-MODULE is an MIT-licensed KiCad breakout (l3wi). It wants a 5 V supply of at least 1.5 A.
- Band
- 60–64 GHz FMCW
- Antennas
- 4 RX / 3 TX in package
- Cores
- Cortex-R4F + C674x DSP
- Memory
- 1.75 MB on-chip RAM
- Package
- 15 × 15 mm FCBGA
- Breakout
- IWR-AOP-MODULE
- Credit
- l3wi
- License
- MIT
Antennas in the package mean no RF layout of your own. The on-chip DSP and accelerator do the heavy math, so a small host board just reads the results.
Datasheet (TI) →05Bench
Sponsor — not part of the issueBench: sponsor
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