A 34 × 18 mm board with a USB-C plug on one end and a USB-C receptacle on the other. It sits between a charger and your phone or laptop, lets power through, and keeps data out. The point is juice jacking: airport, hotel and train USB ports that might want more than to charge your phone.
To be fair, the odds of a real juice jacking attack are close to zero. But it made a great first PCB, and the peace of mind is worth a lot.
Most data blockers are USB-A (eww) and stop at 5 V. airlock is USB-C, passes PD through, and has LEDs so you can see the negotiated voltage at a glance.
What it does
- Data is always blocked. D+/D−, SuperSpeed and SBU aren't connected at all. D+ is shorted to D− on each side, so older phones still see a "dedicated charger" and pull up to 1.5 A.
- PD position: the CC lines pass straight through, so 9 / 15 / 20 V negotiate normally. Up to 20 V × 5 A with a 5 A e-marked cable.
- LOCK position: a 1 µF capacitor from each CC line to ground drowns out PD's 300 kHz signalling, so no PD message gets through in either direction. The plain USB-C current advertisement still does, so you get 5 V at up to 3 A, depending on the charger.
- LEDs: green for LOCK, blue for PD, and a three-LED bar that lights above roughly 7, 13 and 18 V. 9 V lights one, 15 V two, 20 V all three.
Flip the switch, then replug: a PD contract that's already running survives the flip. Most laptops need PD to charge at all, so LOCK is really for phones, earbuds and other small things.
Build
Four layers, 1.0 mm thick so the plug's legs fit, black with white silkscreen. Everything except the plug's back row of pins is surface-mount, made to be stencilled and reflowed on a hot plate.
It's my first PCB, and v1 is being made at JLCPCB right now (pls sponsor me).
Getting one
Once v1 is built and tested, I'll sell it on Tindie. I bought 10 PCB's so expect 6-7 for sale in the first batch. I'll happily make more if there's demand. Each one comes assembled and tested, in a quality 3D-printed enclosure that keeps the board safe in your bag, with the LEDs glowing through the lid. The Buy button up top goes live when they're listed.