AD7124 Temperature Controller

A Zephyr application for reading temperature from the AD7124 24-bit ADC's on-chip temperature sensor.

Overview

This application demonstrates SPI communication with the Analog Devices AD7124 ADC, configured to continuously read from its internal temperature sensor. The temperature readings are logged to the console every 3 seconds.

Hardware Requirements

• Board: STM32 Nucleo-H563ZI (or compatible STM32 board)
• ADC: AD7124 (or AD7124-4/AD7124-8)
• Connections:
  • SPI1_SCK: PA5
  • SPI1_MISO: PG9
  • SPI1_MOSI: PB5
  • SPI1_CS: PD14 (GPIO, active low)

Features

• SPI Mode 3 (CPOL=1, CPHA=1) communication
• Continuous conversion mode
• On-chip temperature sensor reading (±1°C typical accuracy)
• Automatic ADC configuration:
  • Bipolar mode
  • Internal 2.5V reference with buffers enabled
  • SINC3 digital filter
  • PGA gain = 1
• Temperature conversion formula calibrated for AD7124 internal sensor
• Robust error handling and status logging

Building

Prerequisites

1. Zephyr SDK installed
2. Zephyr workspace set up
3. West tool configured

Build Commands

# From the project directory
west build -b nucleo_h563zi

# Clean build
west build -b nucleo_h563zi --pristine

# Flash to board
west flash

Configuration

Key Configuration Options (prj.conf)

• CONFIG_SPI=y - Enable SPI driver
• CONFIG_ADC=y - Enable ADC subsystem
• CONFIG_ADC_AD7124=y - Enable AD7124 driver
• CONFIG_CPP=y - Enable C++ support
• CONFIG_LOG=y - Enable logging
• CONFIG_CBPRINTF_FP_SUPPORT=y - Enable floating-point printf support

Device Tree

The board-specific configuration is in boards/nucleo_h563zi.overlay, which defines:

• SPI1 pin mappings
• Chip select GPIO
• AD7124 device node with SPI mode settings

Usage

After flashing, connect a serial terminal to the board's USB virtual COM port (115200 baud). You should see output similar to:

[00:00:00.000,000] <inf> ad7124: AD7124 on-chip temperature controller
[00:00:00.003,000] <inf> ad7124: CFG0=0x0fe0 CH0=0x8211 ADC_CTRL=0x0100
[00:00:00.003,000] <inf> ad7124: Waiting for first ready...
[00:00:00.010,000] <inf> ad7124: DATA=0x800d42  Temp≈25.32 °C
[00:00:03.010,000] <inf> ad7124: DATA=0x800d41  Temp≈25.31 °C
[00:00:06.010,000] <inf> ad7124: DATA=0x800d43  Temp≈25.33 °C

Code Structure

• src/main.cpp - Main application code
  • SPI read/write helpers
  • AD7124 register definitions
  • Temperature sensor configuration
  • Continuous reading loop
  • Temperature conversion algorithm

Temperature Conversion

The internal temperature sensor outputs are converted using:

temp_celsius = (code - 8388608) / 13584.0 - 272.5

Where code is the 24-bit offset binary ADC result. This formula is based on the AD7124 datasheet's internal temperature sensor specifications.

Customization

Changing Sample Rate

Modify the REG_FILTER0 value in config_temp():

wr24(REG_FILTER0, 0x060180);  // Current setting
// Lower values = faster sampling, higher noise
// Higher values = slower sampling, lower noise

Changing Reading Interval

Adjust the sleep time in the main loop:

k_msleep(3000);  // Current: 3 seconds

Using External Inputs

To measure external analog inputs instead of temperature, modify the config_temp() function to configure different channel inputs. Refer to the AD7124 datasheet for analog input pin assignments.

References

• AD7124 Datasheet
• Zephyr SPI API Documentation
• STM32H563ZI Reference Manual