EMG Board Design Specifications
Thought
Work done
- Reviewed datasheets and pin mapping for the main blocks: U1, U2, U3, IC1, and U4
- Confirmed connector and clock resources for J1, J2, J3, J4, J5, Y2, and Y3
- Added the missing support passives and RF parts needed to complete the design, including the buck inductor L1, RF matching inductor L2, and antenna AE1
- Resolved several implementation details from datasheets, including the ADS1298 input/power pins, BQ24075 charger strap guidance, nRF52840 decoupling requirements, USBLC6 line mapping, and candidate Nordic RF match values
Success criteria review
- ✅ The major functional blocks are selected and present in the schematic: EMG AFE, MCU, USB/charging, battery input, buck regulator, and external connectors
- ✅ Key supporting components for power, clocks, I2C pull-ups, USB-C CC resistors, and RF matching were added
- ❌ The schematic is not yet wired: nets are still incomplete, so SPI, I2C, EMG inputs, USB, charger, and power rails are not fully implemented
- ❌ The layout stage is not yet completed: the 6-layer stackup, 50 ohm RF guidance, placement, and manufacturability checks still need to be applied
- ❌ Final clarification-dependent items are still open in practice: the U3 VSET selection should be finalized against the datasheet table, and the U2 to AE1 RF matching values should be aligned to the Nordic reference for the chosen antenna/layout
Next steps
I am blocked by credit exhaustion, so I cannot make more project changes in this run. The next concrete steps are to wire the full schematic around U1, U2, U3, IC1, J1, J3, and J4; correct any remaining value mismatches; then proceed to PCB layout setup with the required 6-layer stackup, board sizing, and component placement.
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Design Notes
System architecture
- 8 differential EMG channels enter through a 16-position 0.5 mm FFC/FPC connector and feed an 8-channel biopotential AFE/ADC over direct differential inputs.
- The AFE/ADC communicates to the nRF52840 over SPI, with an interrupt/data-ready line for sample timing.
- A 4-position 0.5 mm FFC/FPC connector carries external I2C plus 3.3 V and GND.
- USB-C provides 5 V input, USB data to the nRF52840 native USB pins, and charging input to a single-cell LiPo charger with power-path management.
- The charger SYS rail feeds a dedicated buck converter that generates the main 3.3 V rail.
- The nRF52840 uses an external chip antenna through a configurable matching network and series RF jumper resistor.
Initial part selections
- ADC/AFE: ADS1298IPAG class 8-channel biopotential AFE with integrated PGA and lead-off features.
- MCU/RF: nRF52840-QIAA-R with native USB and external RF matching network.
- Charger: BQ24075TRGTR for USB-powered single-cell LiPo charging with power-path management.
- Buck: TPS62840DLCR for low-IQ 3.3 V generation from the charger SYS rail / battery domain.
- Connectors: 16-pin 0.5 mm FPC for EMG inputs, 4-pin 0.5 mm FPC for I2C/power, USB-C receptacle, JST-PH battery connector.
Layout intent
- Use a JLC-compatible 6-layer stackup.
- Keep the analog EMG front end isolated from the buck and RF section.
- Route the RF feed as a short 50-ohm coplanar microstrip with adjacent ground stitching.
System architecture
Initial part selections
Layout intent
