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The PGA309 is a smart programmable analog signal conditioner used with resistive bridge sensors. It is a complete signal conditioner with bridge excitation, initial span and offset adjustment, temperature adjustment of span and offset, internal/external temperature measurement capability, output over-scale and under-scale limiting, fault detection, and digital calibration.

The calibration is done via one-wire digital serial interface or through a Two-wire industry standard connection. For more information please refer to the pga309 User Guide

The library is written for esp32 so the following pin configuration needs to be taken into account. Any other microcontroller can also be interfaced with pga309, please refer to supported functionality section.

The project is developed in Visual studio code under the PlatformIO extension. The code supports official docuemntation from espressifs. The structure of the files is shown below:

- esp-idf 
  -> .vscode
  -> include 
  -> lib
     -> pga309
        --> pga309.h
        --> pga309.c
  -> src
     --> strainGauge_main.c
  -> test
  -> ...
  -> platformio.ini
  
 - scripts
   --> pga309_register_calculation.m

The strainGauge_main.c file contains minimal application example code with resistive strain gauges.

pga309 is a complete signal conditioner with bridge excitation, initial span and offset adjustment, temperature adjustment of span and offset, internal/external temperature measurement capability, output over-scale and under-scale limiting, fault detection, and digital calibration.

This library only supports some of the functionalities which includes bridge excitation and linearization control, fine offset, fine gain adjustment and pga coarse offset adjustment

There are two digital interfaces on the pga309, one wire and two wire interfaces. The PRG PIN uses a one wire interface (UART Compatible) while external EEPROM uses the two wire interface for programming and reading. This library only supports one wire interface and communication with the pga309.

The library is written in C language for esp32 but any other microcontroller can be used with just slight modification in the espressif's APIs.

The scripts folder contains pga309_register_calculation.m This file can be used to calculate the internal register map values. The following things need to be configured according to your desired application and resistive bridge specifications.

FSS = 1.5e-3; %Full scale sensitivity of the bridge sensor
Vos = 0; %offset voltage in mV
Vref = 3.3; %Reference voltage applied across pga309. 
Vb = 2.7; %bridge voltage across sensor
Rbrg = 120; %Bridge resistance in ohms
Vout_min = 0.5; %Desired minimum output voltage 
Vout_max = 2.5; %Desired maximum output voltage

The strainGauge_main.c contains a minimum application example for resistive strain gauges. The following struct needs to be changed according to your desired application,

static config_t config = {
    .FSS = 0.0015,
    .Vb = 2.7,
    .Vout_min = 0.5,
    .Vout_max = 2.5,
    .Vref = 3.3,
    .FEG = 128,
    .GO = 4.5,
};

For gain settings: please refer to the PGA309 User Guide, the following structure variables has to be modified:

static reg4_t reg4_data = {
    .FEG = 16,                /* Front End Gain*/
    .GO = 2,                  /* Output Amplifier Gain*/
    .Coarse_Offset = -4.25,   /* Coarse Offset Adjustment*/
};

PGA309 consists of seven registers. 4 out of 7 internal registers can be modified with the help of this library. Additional functionalities can be adapted according to the application requirements. The library supports:

• register 1 (Fine Offset Adjust - Zero DAC)
  
• register 2 (Fine Gain Adjust - Gain Adjust)
  
• register 3 (Reference control and Linearization Register)
  
• register 4 (PGA Coarse Offset Adjust and Gain Control)
  

1. PGA309 User Guide
2. ESP32 esp-idf official API Documentation