Request for Review of Four-Layer PCB Design for Low Power Wearable Electronics with nRF52840

[LoPow@]

Dear nRF Support Team and Community Members,

I hope this message finds you well. I am currently working on a low power wearable electronics project. This is my first attempt at designing a four-layer PCB using Altium software, and I would greatly appreciate your expert review and feedback on my design.

Project Overview:

• Project Name: Low Power Wearable Device (LPWD)
• Objective: To develop a low power wearable device aimed at health monitoring applications.
• Key Features:
  • BLE (Bluetooth Low Energy) connectivity using nRF52840
  • Integrated sensors:
    • Accelerometer: BMA400
    • Humidity and Temperature: HTS221
    • Pressure: LPS22HH
    • Color: BH1749
  • Recommended antenna: AN91445
  • Target Power Consumption: 1-5mW

Files for Review:

• Schematic: Schematic of LPWD.pdf
• Gerber Files: Gerber of LPWD.zip

Areas of Concern:

1. Pin Assignments: Verification of correct pin assignments and connections for the nRF52840 and sensors.
2. Component Values: Validation of passive component values and their suitability for the circuit.
3. Power Management: Assessment of the power management circuitry for potential issues and efficiency.
4. RF Layout: Review of the RF section, including the antenna, to ensure optimal signal integrity and performance.
5. Overall Layout: General feedback on the PCB layout and routing, particularly with respect to signal integrity and power distribution.
6. Sensor Integration: Proper integration and placement of the accelerometer, humidity and temperature sensor, pressure sensor, and color sensor.

Additional Information:

• The design aims to minimize power consumption while maintaining reliable operation of the sensors and BLE communication.
• Ensuring good RF performance and low noise is critical for this wearable device.

I have attached the schematic in PDF format and a ZIP file containing the Gerber files for your convenience. Your insights and feedback will be invaluable to ensure the robustness and reliability of this design.

Thank you in advance for your time and assistance. I look forward to your expert guidance.

[ketiljo]

Hi

I've taken a look at the design. The schematic looks correct as far as I can see. 

For the layout, I see that this isn't finished. But make sure you use inner layer 1 as ground and not as a power plane. A power plane is too noisy for the first inner plane, but can be used as the second inner layer. 

The RF section is ok. The antenna's load arm needs to be grounded.

Best regards,

Ketil Aas-Johansen

[LoPow@]

I have attached my PCB design file and would appreciate it if someone could recheck it for me. I want to ensure there are no errors or issues that I might have overlooked. Your expertise and feedback would be invaluable.

Here are the layer details:

• Red: Top layer
• Brown: Mid layer 1 
• Light blue: Mid layer 2
• Dark blue: Bottom layer

Thank you in advance for your help!

.

[ketiljo]

1. Chech the app note where you found the antenna, but I assume the inner and bottom layers needs to be removed under the antenna:

2. This part of the antenna needs to be grounded: 

3. Mid layer 1 can't be a power place, it must be ground. Swap the inner layets. 

[LoPow@]

Can you please check this?

Top Layer : 

Mid Layer 1 : 

Mid Layer 2 : 

Bottom Layer : 

All Layer : 

Also comment on the USB port for programming & suggest the smaple code.

[AHaug]

Hi,

Ketil is on vacation until the coming week so there will unfortunately be some waiting. He'll update you when he gets back.

Kind regards,
Andreas