# Resonate Pendant ## Description Resonate Pendant golden reference design. Board is a 39 mm x 63 mm portrait rectangle with 5 mm corner radii, 2-layer FR4, 0.8 mm thickness, 1 oz copper on both layers, matte black top solder mask, no bottom solder mask, ENEPIG finish, and no silkscreen on either side. Allowed components only: U1 STM32L052C8T6, U2 CH340E, U3 BQ24210DQCT, C1 10uF, C2 4.7uF, C3-C7 100nF, R1 24k, R2 1k, R3 10k, D1 green 0402 LED, MAG1-MAG4 magnetic pads, J1 solar solder pads, J2 battery solder pads, TP1-TP4 test pads. Required top artwork: golden-ratio grid lines and gold circles on F.Cu with mask openings, decorative only, 0.8-1.0 mm width, at least 0.5 mm from active traces. Required bottom artwork: exposed ENEPIG bottom copper split into FREQ_OUT 61.8 percent and GND 38.2 percent with an exact 0.20 mm S-curve isolation gap, no vias through bottom except one PA4-to-FREQ_OUT via at the extreme edge. Functional requirements: MAG1 and J1 VIN feed U3 IN, U3 OUT feeds J2 battery pad and system VBAT, MAG2 to U2 UD+, MAG3 to U2 UD-, MAG4 to common ground, U2 TX to U1 PA10, U2 RX to U1 PA9, U1 PA4 to bottom FREQ_OUT, U1 PA5 to R2 then D1 to GND, U3 ISET to R1 to GND, U3 TS to R3 to GND, decoupling exactly as specified. Prohibited items: external crystal, JST connectors, wireless module, antenna, separate regulator IC, ESD protection IC, USB-C connector, through-hole parts, bottom solder mask, silkscreen, more than three ICs, or any unapproved substitutions. ## Project Details - **Owner:** bbridgers - **Created:** 4/2/2026 - **Last Updated:** 4/2/2026 - **Visibility:** Public - **Layer Count:** 2-layer - **Bottom Electrode Split:** FREQ_OUT 61.8% / GND 38.2% with 0.20mm S-curve gap - **Bottom Solder Mask:** None - **Allowed Bottom Via Exception:** Single PA4 to FREQ_OUT edge via only - **Copper Weight:** 1 oz - **Top Solder Mask:** Matte Black - **Surface Finish:** ENEPIG - **Board Thickness:** 0.8mm - **Max Component Height:** 1.5mm - **Silkscreen:** None ## Key Components ### D1 — [LTST-C281KGKT](https://www.flux.ai/lcsc/ltst-c281kgkt~ltex.md) - Package: LED0402-RD_GREEN - Datasheet URL: https://storage.googleapis.com/graviton-electric-symbols/document_assets/lcsc/1810231610_Lite-On-LTST-C281KGKT_C160479.pdf - Manufacturer Name: LITEON(光宝) - LCSC Part Number: C160479 - Role: Status LED - Product Info Url: https://lcsc.com/product-detail/Others_Lite-On-LTST-C281KGKT_C160479.html - JLCPCB Part Class: Extended Part - Manufacturer Part Number: LTST-C281KGKT - Role Details: Green 0402 status LED stand-in for intended YLED0402G - Part Type: Light Emitting Diodes (LED) - Package or Case Code: LED0402-RD_GREEN **Pins:** - A [pin 2] - K [pin 1] ### D2 — [BAT54C-7-F](https://www.flux.ai/lcsc/bat54c-7-f~xpzb.md) - JLCPCB Part Class: Extended Part - Datasheet URL: https://storage.googleapis.com/graviton-electric-symbols/document_assets/lcsc/1809200026_Diodes-Incorporated-BAT54C-7-F_C134405.pdf - LCSC Part Number: C134405 - Product Info Url: https://lcsc.com/product-detail/Schottky-Barrier-Diodes-SBD_DIODES_BAT54C-7-F_BAT54C-7-F_C134405.html - Package: SOT-23-3_L2.9-W1.6-P1.90-LS2.8-BR - Part Type: Schottky Barrier Diodes (SBD) - Manufacturer Name: DIODES(美台) - Package or Case Code: SOT-23-3_L2.9-W1.6-P1.90-LS2.8-BR - Role Details: Target A dual Schottky diode between USB input and charger input - Role: Input Protection - Manufacturer Part Number: BAT54C-7-F **Pins:** - A [pin 2] - A [pin 1] - K [pin 3] ### U1 — [STM32L052C8T6](https://www.flux.ai/lcsc/stm32l052c8t6~ju4f.md) - Role: Main MCU - Datasheet URL: https://storage.googleapis.com/graviton-electric-symbols/document_assets/lcsc/2304140030_STMicroelectronics-STM32L052C8T6_C111213.pdf - Role Details: Golden reference MCU; PA10 UART RX from U2 TX, PA9 UART TX to U2 RX, PA4 FREQ_OUT, PA5 LED drive - Manufacturer Part Number: STM32L052C8T6 - LCSC Part Number: C111213 - Package: LQFP-48_L7.0-W7.0-P0.50-LS9.0-BL - Package or Case Code: LQFP-48_L7.0-W7.0-P0.50-LS9.0-BL - Manufacturer Name: ST(意法半导体) - Part Type: ST Microelectronics - Product Info Url: https://lcsc.com/product-detail/ST-Microelectronics_STMicroelectronics_STM32L052C8T6_STM32L052C8T6_C111213.html **Pins:** - BOOT0 [pin 44] - NRST [pin 7] - PA0 [pin 10] - PA1 [pin 11] - PA10 [pin 31] - PA11 [pin 32] - PA12 [pin 33] - PA13 [pin 34] - PA14 [pin 37] - PA15 [pin 38] - PA2 [pin 12] - PA3 [pin 13] - PA4 [pin 14] - PA5 [pin 15] - PA6 [pin 16] - PA7 [pin 17] - PA8 [pin 29] - PA9 [pin 30] - PB0 [pin 18] - PB1 [pin 19] - PB10 [pin 21] - PB11 [pin 22] - PB12 [pin 25] - PB13 [pin 26] - PB14 [pin 27] - PB15 [pin 28] - PB2 [pin 20] - PB3 [pin 39] - PB4 [pin 40] - PB5 [pin 41] - PB6 [pin 42] - PB7 [pin 43] - PB8 [pin 45] - PB9 [pin 46] - PC13 [pin 2] - PC14-OSC_IN [pin 3] - PC15-OSC32_OUT [pin 4] - PH0-OSC_IN [pin 5] - PH1-OSC_OUT [pin 6] - VDD [pin 48] - VDD [pin 24] - VDD [pin 1] - VDD_USB [pin 36] - VDDA [pin 9] - VSS [pin 35] - VSS [pin 23] - VSS [pin 47] - VSSA [pin 8] ### U2 — [CH340E](https://www.flux.ai/kicad-part-library/ch340e~64.md) - Package: MSOP-10 - Role: USB UART Bridge - Manufacturer Part Number: CH340E - Role Details: Golden reference USB-to-UART bridge for MAG2/MAG3 data pads to MCU UART - Package or Case Code: MSOP-10_3x3mm_P0.5mm - Datasheet URL: https://www.mpja.com/download/35227cpdata.pdf **Pins:** - ~{CTS} [pin 5] - ~{RTS} [pin 4] - GND [pin 3] - RXD [pin 9] - TNOW [pin 6] - TXD [pin 8] - UD- [pin 2] - UD+ [pin 1] - V3 [pin 10] - VCC [pin 7] ### U3 — [BQ24210DQCR](https://www.flux.ai/lcsc/bq24210dqcr~1bgc.md) - Manufacturer Name: TI(德州仪器) - Package: WSON-10_L3.0-W2.0-P0.50-BL-EP - Product Info Url: https://lcsc.com/product-detail/PMIC-Battery-Management_Texas-Instruments-Texas-Instruments-BQ24210DQCR_C524795.html - Role: Battery Charger - JLCPCB Part Class: Extended Part - Part Type: Battery Management ICs - Datasheet URL: https://storage.googleapis.com/graviton-electric-symbols/document_assets/lcsc/2005121707_Texas-Instruments-BQ24210DQCR_C524795.pdf - LCSC Part Number: C524795 - Role Details: Closest available library stand-in for required BQ24210DQCT; preserve exact charger connectivity and intent - Manufacturer Part Number: BQ24210DQCR - Package or Case Code: WSON-10_L3.0-W2.0-P0.50-BL-EP **Pins:** - ~{CHG} [pin 8] - ~{EN} [pin 7] - ~{PG} [pin 6] - BAT [pin 10] - EP [pin 11] - ISET [pin 2] - TS [pin 5] - VBUS [pin 1] - VDPM [pin 9] - VSS [pin 3] - VTSB [pin 4] ### U4 — [AP7361C-33FGE-7](https://www.flux.ai/lcsc/ap7361c-33fge-7~fz0x.md) - Role Details: Target A 3.3V regulator fed from /VBAT and supplying +3.3V - Part Type: Linear Voltage Regulators (LDO) - Datasheet URL: https://storage.googleapis.com/graviton-electric-symbols/document_assets/lcsc/2304140030_Diodes-Incorporated-AP7361C-33FGE-7_C151007.pdf - Manufacturer Part Number: AP7361C-33FGE-7 - Product Info Url: https://lcsc.com/product-detail/Low-Dropout-Regulators-LDO_DIODES_AP7361C-33FGE-7_AP7361C-33FGE-7_C151007.html - Manufacturer Name: DIODES(美台) - Role: LDO Regulator - Package or Case Code: DFN-8_L3.0-W3.0-P0.65-BL-EP - JLCPCB Part Class: Extended Part - LCSC Part Number: C151007 - Package: DFN-8_L3.0-W3.0-P0.65-BL-EP **Pins:** - ADJ/NC [pin 3] - EN [pin 5] - EXP [pin 9] - GND [pin 4] - IN [pin 8] - NC [pin 6] - NC [pin 2] - NC [pin 7] - OUT [pin 1] ### USB1 — [XY PZ2.54-1x4P ZD](https://www.flux.ai/lcsc/xy-pz2p54-1x4p-zd~rglc.md) - Manufacturer Name: XYECONN(辛译) - Role: USB Breakout Connector - LCSC Part Number: C54110161 - JLCPCB Part Class: Extended Part - Package: 1x4 2.54 mm - Package or Case Code: CONN-TH_PZ2.54-1X4-11.2 - Role Details: Target A equivalent for HX PZ2.54-1x4P TP-YQ carrying VBUS, D-, D+, and GND - Manufacturer Part Number: XY PZ2.54-1x4P ZD **Pins:** - 1 [pin 1] - 2 [pin 2] - 3 [pin 3] - 4 [pin 4] *The full schematic, PCB layout, bill of materials, and interactive design are available at [https://www.flux.ai/bbridgers/resonate-pendant~u0](https://www.flux.ai/bbridgers/resonate-pendant~u0).* --- *Generated from [https://www.flux.ai/bbridgers/resonate-pendant~u0](https://www.flux.ai/bbridgers/resonate-pendant~u0)*