PCB Redesign – HX711 Half-Bridge & BLE Integration
Budget: $250 – $750 USD
Circuit Review & Revision Brief – HX711 Half-Bridge + BLE (Xiao nRF52840)
Project Overview: I’ve had a custom PCB designed to measure strain via a half-bridge Wheatstone circuit using 120Ω strain gauges, with signal acquisition via the HX711 and wireless transmission over BLE. The current version uses an ESP32, but it needs to be updated to use the Seeed Xiao nRF52840 due to its compact size and native BLE capabilities.
I'm looking for a skilled reviewer to:
- Review the existing schematic and PCB for electrical and layout correctness.
- Revise the design based on updated hardware, connectivity, and power requirements.
- Deliver all files necessary to manufacture the updated board via JLCPCB.
- Key Design Requirements & Changes:
1. MCU Upgrade:
Replace ESP32 with Seeed Xiao nRF52840.
Ensure BLE transmission and necessary GPIOs (for HX711 and other components) are properly mapped.
Make sure USB-C programming and SWD debugging capabilities are preserved.
2. Strain Gauge Configuration (Half-Bridge):
Two 120Ω strain gauges, both under strain in the same direction.
Must be configured to add their resistance changes (not cancel), in a true half-bridge Wheatstone setup.
Properly route signal through HX711’s A+ and A−, and excitation through E+ and E−.
3. HX711 Wiring:
Connect DT and SCK lines to appropriate nRF52840 GPIOs.
Confirm filtering and decoupling around analog signal lines and power rails are present and appropriately placed.
4. Replace Surface Pads with JST Connectors:
The current version uses surface mount pads for external devices—replace these with JST-PH (or similar) connectors for:
2x Strain Gauges
1x LiPo Battery
All connectors must be clearly labeled and keyed to avoid incorrect insertion.
Preferred JST footprint: 2-pin for battery, 3- or 4-pin as needed for gauges.
5. Power and Charging:
Power will be supplied via a single-cell LiPo battery.
Critical: When a battery is connected to the board, plugging in USB-C to the Xiao nRF52840 must allow the battery to charge safely.
If a charging IC is required (e.g., TP4056, MCP73831), confirm it is:
Properly wired to both battery and USB-C 5V line
Compliant with safe charging profiles for typical LiPo cells
Includes any required indicators or protection circuitry
6. Optional Protections (Preferred):
Reverse-polarity protection on battery input
Current-limiting or ESD protection for exposed JST lines
Deliverables Required:
Updated schematic and PCB layout
All JLCPCB-ready production files:
Gerber files
Pick and Place file
BOM (with LCSC part numbers if possible)
Optional but appreciated:
3D render of final board for visual check
Highlighted callouts of all external JST connectors
Project Overview: I’ve had a custom PCB designed to measure strain via a half-bridge Wheatstone circuit using 120Ω strain gauges, with signal acquisition via the HX711 and wireless transmission over BLE. The current version uses an ESP32, but it needs to be updated to use the Seeed Xiao nRF52840 due to its compact size and native BLE capabilities.
I'm looking for a skilled reviewer to:
- Review the existing schematic and PCB for electrical and layout correctness.
- Revise the design based on updated hardware, connectivity, and power requirements.
- Deliver all files necessary to manufacture the updated board via JLCPCB.
- Key Design Requirements & Changes:
1. MCU Upgrade:
Replace ESP32 with Seeed Xiao nRF52840.
Ensure BLE transmission and necessary GPIOs (for HX711 and other components) are properly mapped.
Make sure USB-C programming and SWD debugging capabilities are preserved.
2. Strain Gauge Configuration (Half-Bridge):
Two 120Ω strain gauges, both under strain in the same direction.
Must be configured to add their resistance changes (not cancel), in a true half-bridge Wheatstone setup.
Properly route signal through HX711’s A+ and A−, and excitation through E+ and E−.
3. HX711 Wiring:
Connect DT and SCK lines to appropriate nRF52840 GPIOs.
Confirm filtering and decoupling around analog signal lines and power rails are present and appropriately placed.
4. Replace Surface Pads with JST Connectors:
The current version uses surface mount pads for external devices—replace these with JST-PH (or similar) connectors for:
2x Strain Gauges
1x LiPo Battery
All connectors must be clearly labeled and keyed to avoid incorrect insertion.
Preferred JST footprint: 2-pin for battery, 3- or 4-pin as needed for gauges.
5. Power and Charging:
Power will be supplied via a single-cell LiPo battery.
Critical: When a battery is connected to the board, plugging in USB-C to the Xiao nRF52840 must allow the battery to charge safely.
If a charging IC is required (e.g., TP4056, MCP73831), confirm it is:
Properly wired to both battery and USB-C 5V line
Compliant with safe charging profiles for typical LiPo cells
Includes any required indicators or protection circuitry
6. Optional Protections (Preferred):
Reverse-polarity protection on battery input
Current-limiting or ESD protection for exposed JST lines
Deliverables Required:
Updated schematic and PCB layout
All JLCPCB-ready production files:
Gerber files
Pick and Place file
BOM (with LCSC part numbers if possible)
Optional but appreciated:
3D render of final board for visual check
Highlighted callouts of all external JST connectors
Related categories:
Microcontroller
Electrical Engineering
PCB Layout
Circuit Design
Bluetooth Low Energy (BLE)