Precision Strain Gauge Amplifier PCB Design

Hi, I need help designing a precision strain gauge amplifier PCB for a pedal force sensor (PFS) project. Please read the requirements carefully.

Project Overview

Application: Pedal force measurement system

Sensor: 350Ω full-bridge strain gauge

Force range: 0 to 150 kg

System requires both analog output and digital display (kg)

Core Requirements
1. Analog Signal Conditioning Circuit

Use INA333 (or equivalent modern low-noise instrumentation amplifier)

Stable 5V bridge excitation using precision reference (e.g., REF5050 + buffer)

Output range:

Preferably 0–3.3V (acceptable: 0–5V)

Gain designed for full-scale (150 kg)

Include:

Gain adjustment (trim or precision resistor)

Offset/zero adjustment (via REF pin or equivalent)

Proper low-pass filtering (~20–30 Hz)

Output buffer (rail-to-rail op-amp like OPA333 or similar)

2. Parallel Digital Measurement (HX711)

Same strain gauge signal must also feed:

HX711 module (no pre-amplification before HX711)

HX711 will be used with:

TM1637 7-segment display module (to show weight in kg)

Ensure:

No signal interference between analog and HX711 paths

Proper high-impedance connection and grounding strategy

3. PCB Design Requirements

2-layer PCB with solid ground plane

Proper analog and digital ground separation (star grounding)

Differential routing for strain gauge signals

Noise minimization (very important — low-level mV signals)

Compact and practical layout

Suitable connectors for:

Strain gauge (4-wire)

Analog output

HX711 interface

4. Deliverables Required

Complete schematic (PDF + source file)

PCB layout (Gerber + design files)

BOM (components easily available in India preferred)

Brief design notes:

Gain calculation

Calibration method (kg vs voltage)

Important Notes

This is a precision analog design, not a generic amplifier module

Avoid using outdated ICs like AD620 unless justified

Focus on:

Low noise

Stability

Repeatability

Goal

To build a reliable, low-noise