Battery-less Audio Node Design


I’ll turn this concept into a grounded project specification first, then verify whether the named off-the-shelf parts can actually support a 2 mm³ battery-less audio/RF node before attempting a schematic. I’ll rename the blank project, capture the requirements, and do a feasibility/power-component check against available part data.
I renamed the project and captured the concept in Project Specification. I also completed a datasheet-grounded feasibility check in Feasibility and Power Analysis.
Conclusion: the exact 2 mm cube off-the-shelf design should not proceed to schematic as stated—the microphone and EFR32-class SoC packages alone exceed the volume, and the 01005 buffer capacitor is orders of magnitude too small for RF/audio burst energy. Recommended next step is to choose a revised target: larger proof-of-concept PCB, true custom bare-die/SiP research package, or reduced-function NFC-style node.
Design a larger proof-of-concept PCB around these components.
I’ll design a practical proof-of-concept schematic around the same RF SoC, PDM mic, Schottky rectifier, and GRM02 buffer concept. I’ll size the power path first, add the components and support circuitry, wire the schematic, then run review and document the firmware/power notes.
Designed the larger proof-of-concept schematic around the EFR32MG22, SPK0641HT4H-1 mic, SMS7621 rectifier bridge, GRM02 benchmark capacitor, larger reservoir cap, AP2112K 3.3 V rail, SMA RF test port, coil input, SWD header, reset, decoupling, and RF match.
I documented the implementation in Proof-of-Concept Design Notes and added firmware bring-up guidance in Firmware Starter. Schematic connectivity is complete; remaining review issues are expected layout airwires and generic-part MPNs to resolve before fabrication. Next step is PCB layout setup and placement—ready when you want me to proceed.
Set board stackup
Auto-place components
Run ERC/DRC
Resolve BOM MPNs
Add test points

U2
D1 2 - D2 2
U1 PAVDD - C3 P1
U1 IOVDD - U1 RFVDD
D1 2 - D2 2
U1 PAVDD - C3 P1
U1 PC00 - MK1 CLOCK
L1 P2 - C12 P1
U1 RF2G4_IO - L1 P1
U1 PA01 - J2 Pin_4
D1 2 - D2 2
U1 PA02 - J2 Pin_2
U1 RESETn - R1 P2
U2 EN - C1 P1
U1 PC00 - MK1 CLOCK
J1 P1 - U2 VIN
MK1 SELECT - R2 P1
U1 PAVDD - C3 P1
U2 VOUT - C2 P1
J4 P1 - D1 1
U1 HFXTAL_I - Y1 OSC1
J4 P2 - D2 1
U1 RESETn - R1 P2
U1 DECOUPLE - C7 P1
J4 P2 - D2 1
U1 PA02 - J2 Pin_2
U1 PC01 - MK1 DATA
U1 RESETn - R1 P2
J4 P1 - D1 1
U1 RESETn - R1 P2
U1 HFXTAL_O - Y1 OSC2
U1 HFXTAL_O - Y1 OSC2
U1 HFXTAL_I - Y1 OSC1
U1 PC01 - MK1 DATA
U2 VOUT - C2 P1
J4 P1 - D1 1
U1 PA01 - J2 Pin_4
R3 P2 - R4 P1
U1 IOVDD - U1 RFVDD
J1 P1 - U2 VIN
MK1
C10
Capacitance
0.1µF
U1
D2
D3
D1
J1
J2
J3
J4
S1
MK1 GROUND - C8 P2
MK1 GROUND - C8 P2
D3 1 - D4 1
MK1 GROUND - C8 P2
GND
D3 1 - D4 1
GND
S1 3 - S1 4
GND
S1 3 - S1 4
D3 1 - D4 1
MK1 GROUND - C8 P2
GND
GND
Y1
GND
GND

RF-Harvested Audio Node

RF-Harvested Audio Node thumbnail