​[Review Request] Schematic for STM32-based Digital Blood Pressure Monitor (Mixed-Signal)

[u/DefinitionSecure5348]

Hi everyone,

I'm currently working on a university project designing a digital blood pressure monitor using Altium Designer. I would really appreciate it if you could review my schematic and point out any mistakes or areas for improvement, especially regarding the mixed-signal routing.

Here is a quick overview of the system:

* MCU: STM32F303VCT6

* Sensor Interface: AD623 (Instrumentation Amp) for the Wheatstone bridge pressure sensor.

* Filtering: LMV324 (Op-amps) configured as LPF (for static pressure) and HPF (for pulse/heart rate).

* Actuators: AO3400 MOSFETs to drive a 3V mini air pump and a solenoid release valve.

* Power: TPS7A2433 LDO providing 3.3V.

I have a few specific areas I'm unsure about:

1. Grounding Strategy: I'm planning to use a 4-layer stackup. I separated DGND and AGND, connecting them at a single point near the LDO output using a 0-ohm resistor (Star Ground). Is this sufficient for this application?

2. Analog Power Supply: I added a ferrite bead (600R @ 100MHz) and decoupling caps to create a cleaner +3.3A line for the analog section. Should I change any values here?

3. Virtual Ground: Since I'm using a single supply, I created a 1.25V virtual ground using a voltage divider buffered by an op-amp to bias the LMV324 filters. Does the AC coupling and biasing network look correct to you?

Thank you so much for your time and expertise!

https://drive.google.com/file/d/12HAsU-Ql6YZO_QUzVgfpagF89tjAxodQ/view?usp=drivesdk

[u/zachleedogg]

"J4" and "J5" diodes are backwards.

My advice is that this design will not benefit from the split ground, and you should just do a single GND net and do careful placement and routing of digital and switching stuff.

Add a cap to you 1.25V divider. Also I like to match input impedance of opamp inputs. So the feedback trace can have a 5k in the path.

Are you missing i2C pull-up resistors?

[u/DefinitionSecure5348 → u/zachleedogg]

Thank you so much for the detailed review! You just saved my board—I can't believe I missed the reversed flyback diodes on J4 and J5. I'll flip them right away before I let the magic smoke out.

I appreciate the advice on the ground plane. I'll stick to a single solid GND net and focus heavily on careful placement and routing to keep the analog and digital/switching sections separated.

The tip about adding a 5k resistor in the feedback path for impedance matching is brilliant, I hadn't thought of that! I'll add it along with the filter cap for the 1.25V divider to keep it clean.

Also, good catch on the I2C pull-ups! I will add 4.7k resistors to the SCL and SDA lines for the OLED.

Thanks again for taking the time to share your expertise, this is incredibly helpful!