Dual active bridge

AirTap: Touchless AC Switch

A touchless, proximity-triggered relay controller for 220 V AC loads. Hold your hand 10–30 mm above the sensing area and a VL53L0X time-of-flight sensor detects it. The ATmega328 then toggles an onboard relay to switch a lamp, fan or other mains appliance, with no physical contact.

Credit: AirTap is a fork of ProxiWave-D (PWD-v010A) by Ampnics, released under the MIT License. The circuit, PCB layout and test firmware are Ampnics' original design. This fork re-brands the board silkscreen as "AIR-TAP", ports the project to KiCad 10, and adds Gerbers, renders and documentation. See NOTICE.md.

⚠️ DANGER: mains voltage. The AC side of this board carries 220 V. Never touch it while it's powered, keep it in an enclosure, and only build it if you're experienced with mains wiring.

3D views

Top	Bottom (sensor side)

Schematic sections

220 VAC → 5 VDC	AC connector, relay & buzzer
ToF sensor	Microcontroller

Layer views

Front copper	Back copper
Front silkscreen	Back silkscreen

Overview

Working Principle

1. Power: mains enters on J1 (LINE / NEUTRAL) through fuse F1 (0.5 A). MOV RV1 (10D561K) clamps surges, and the HLK-5M05 isolated module produces 5 V. The AMS1117 then makes 3.3 V for the ATmega328 and the VL53L0X.
2. Sensing: the VL53L0X sends out infrared laser pulses and measures their time of flight. The ATmega328 reads the distance over I²C (SDA = PC4, SCL = PC5).
3. Decision: when a hand is held inside the calibrated 10–30 mm window, the firmware toggles the load state.
4. Switching: PC2 drives Q1 (AO3400A logic-level MOSFET), which energises relay K1. D1 clamps the coil's flyback spike. The relay's NO / C / NC contacts are brought out on J1.
5. Feedback: PC3 drives the buzzer through Q2, the blue LED shows the relay state, and the green LED (PC1) shows status.

GPIO Mapping

J1: AC Terminal (5-way)

Wire the load between NO and neutral, and connect C to line, so the load is off until triggered.

Key Equations

ToF ranging:

d = (c × t) / 2        c = 3×10⁸ m/s, t = round-trip time of the laser pulse

Relay coil drive (G5LE-1, 5 V coil ≈ 72 Ω):

I_coil ≈ 5 V / 72 Ω ≈ 70 mA      → switched by AO3400A (R_DS(on) ≈ 30 mΩ at V_GS = 2.5 V)

LED current (3.3 V rail):

I_LED = (3.3 − V_F) / R      e.g. (3.3 − 2.0) / 330 Ω ≈ 4 mA

Specifications

Bill of Materials (key parts)

Plus 0603 resistors, capacitors and LEDs; see the schematic for full values.

Firmware

Test sketches by the original author are in firmware/test-codes/:

Setup: in the Arduino IDE, install MiniCore (board manager URL https://raw.githubusercontent.com/MCUdude/MiniCore/master/package_MCUdude_MiniCore_index.json), then choose ATmega328, External 8 MHz, 3.3 V. Install the VL53L0X library by Pololu, and flash through J2 with a USBasp.

Design Notes

• J3 footprint: the backup IR connector (J3) has no footprint assigned in the schematic, although the PCB has one. Assign it, for example PinHeader_1x03_P2.54mm, before running "Update PCB from Schematic", or KiCad will flag it.
• Isolation: the AC/DC boundary is marked on the silkscreen. For extra safety, consider adding a routed isolation slot between the mains section and the logic section.
• C1 must be an X2-rated safety capacitor.
• Load rating: the relay is rated 10 A, but the fuse (0.5 A) protects the logic supply only. Fuse the load circuit separately, sized for your appliance.
• 3D models: the vendor 3D models (relay, buzzer, terminal, switch) aren't included, so KiCad's 3D viewer shows those parts without a body. The 3D renders in this folder were made with them.

Files in This Folder

How to Use

1. Open airtap.kicad_pro in KiCad 10 or later.
2. To manufacture, zip gerbers/ together with the two .drl files and upload them to any PCB fab.
3. After assembly, flash the test sketches through J2 to check each block, then load your main firmware.
4. Calibrate the trigger distance (10–30 mm) for your enclosure.

License

The original ProxiWave-D design is © Ampnics, released under the MIT License (see NOTICE.md). Changes in this fork are released under the repository's MIT License.