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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Project Specification - Wearable EMG Acquisition PCB
Scope
Design a wearable EMG acquisition PCB with 8 differential biopotential channels through a 16-position flex connector, BLE/USB processing, USB-C charging, LiPo battery power, a 3.3 V buck rail, and a 2.4 GHz antenna path suitable for JLC 6-layer layout.
System Architecture
Diagram
Selected Architecture Defaults
- AFE/ADC architecture: ADS1298-class 8-channel biopotential AFE with integrated PGA, simultaneous sampling, SPI interface, and lead-off based impedance checking.
- MCU architecture: bare nRF52840 with native USB and external 32 MHz plus 32.768 kHz crystals.
- USB role: charging plus native USB device/debug data.
- Charge and power path: BQ24075 charger/power-path device feeding a dedicated 3.3 V buck regulator.
- Main 3.3 V rail: TPS62840 configured for 3.3 V from charger SYS / battery domain.
- RF path: nRF ANT pin through a small series resistor and a 3-element tunable matching network into a 2.4 GHz chip antenna.
- EMG connector mapping: 16 signal pins used as 8 differential pairs, one pair per ADS1298 channel.
- External 4-pin flex mapping: GND, 3.3 V, I2C SDA, I2C SCL.
Functional Blocks
- EMG input flex connector and direct differential routing into the AFE.
- ADS1298 analog front end with reference, VCAP, and lead-off support.
- nRF52840 BLE/USB subsystem with crystals, decoupling, SWD reserve pins, and SPI host connection.
- USB-C sink input with CC pull-downs and ESD protection.
- Single-cell LiPo charger, battery connector, SYS rail, and 3.3 V buck converter.
- RF feed with resistor placeholder, matching pads, and chip antenna.
Pin Mapping Intent
- EMG channels map sequentially from connector J3 pins 1-16 to CH1P/CH1N through CH8P/CH8N.
- SPI between MCU and AFE uses dedicated MCU GPIOs plus DRDY and START control.
- External I2C connector is sourced by the MCU and shares one pull-up pair to 3.3 V.
- USB D+ and D- route directly between the USB connector protection device and the MCU USB pins.
PCB Intent
- Target a JLC-compatible 6-layer stackup.
- Keep the EMG connector and AFE in a quiet analog zone away from the buck and USB charger.
- Keep the antenna at a board edge with full keepout under and around the RF section.
- Route the RF feed as a short 50 ohm coplanar structure with adjacent ground stitching.
- Place USB-C and battery connector on opposite edges to reduce power-noise coupling into the analog front end.
Open Engineering Decisions Resolved For This Revision
- Impedance checking will use ADS1298 lead-off capability rather than adding a second analog front end.
- RF matching will use a tunable placeholder network with default population based on the Nordic reference design, then be optimized in bring-up if needed.
- The design uses the 16-pin EMG flex only for the 8 differential inputs and does not allocate extra pins for driven-reference electrodes in this revision.
Scope
System Architecture
Selected Architecture Defaults
Functional Blocks
Pin Mapping Intent
PCB Intent
Open Engineering Decisions Resolved For This Revision
