DAC Design with PCM1795 and STM32

yes please

Thought for 5 sec

I’ll rebuild this as a real IC-level DAC schematic: PCM1795 pins, three OPA1612 dual op-amps, I/V parts, differential outputs, regulators/connectors, then verify ERC before stopping at the schematic stage.

Thought for 35 sec

flux

I found the previous connector-only blocks. I’m removing those and replacing them with actual ICs and analog-stage components now.

Worked for 10 mins 1 sec

flux

Rebuilt the project as a real IC-level schematic instead of connector blocks: PCM1795, 3× OPA1612, LT3042 3.3 V/5 V rails, I/V feedback networks, differential output stage, RCA outputs, and power/input headers are now present and wired. ERC checks are currently clean for the checks run, and the project spec was updated.

Open items:

The PCB layout is not done yet; per workflow, this is the schematic checkpoint before layout.
The PCM1795 library symbol/footprint must be visually checked against the TI datasheet pinout before fabrication.
STM32F407 exact I2S/SPI GPIO mapping is still your next firmware/pinout decision.

Suggested next steps:

Review the schematic view and confirm it now looks like the detailed circuit you expected.
I can next create the physical PCB placement with DAC + OPA stages tightly clustered.
After placement approval, I can route the board with low-noise analog layout rules.

Proceed to placement

Verify PCM1795 symbol

Explain schematic

Layout best practices

Run deeper review

Files

Schematic

Layout

3D View

Firmware Starter — STM32F407 PCM1795 DAC Source

Platform & Toolchain

MCU board: External STM32F407 board
Framework: STM32 HAL / STM32CubeIDE
Purpose: Generate I2S audio clocks/data and configure PCM1795 over SPI/control pins.

Pin Mapping

Exact STM32 GPIO pins depend on the specific STM32F407 board header wiring. The schematic currently names the board-level connector nets:

Table

Function	Schematic Net	STM32 Peripheral	Direction	Notes
Bit clock	I2S_BCK	SPI/I2Sx_CK	MCU → DAC	Select an STM32 I2S-capable pin.
Word select	I2S_LRCK	SPI/I2Sx_WS	MCU → DAC	Also called LRCK/WS.
Audio data	I2S_DATA	SPI/I2Sx_SD	MCU → DAC	PCM audio data stream.
Master clock	I2S_MCLK	SPI/I2Sx_MCK	MCU → DAC	Use if the PCM1795 board requires external MCLK.
Control clock	SPI_SCK	SPIx_SCK	MCU → DAC	PCM1795 control port.
Control data in	SPI_MOSI	SPIx_MOSI	MCU → DAC	Register writes.
Control data out	SPI_MISO	SPIx_MISO	DAC → MCU	Optional, if DAC board exposes readback.
Chip select	DAC_CS	GPIO output	MCU → DAC	Active level to confirm from board.
Reset	DAC_RST	GPIO output	MCU → DAC	Active level to confirm from board.
Mute	DAC_MUTE	GPIO output	MCU → DAC	Active level to confirm from board.

Example STM32 HAL Source Skeleton

C
#include "main.h"
#include <string.h>

I2S_HandleTypeDef hi2s3;
SPI_HandleTypeDef hspi1;

#define DAC_CS_GPIO_Port     GPIOA
#define DAC_CS_Pin           GPIO_PIN_4
#define DAC_RST_GPIO_Port    GPIOA
#define DAC_RST_Pin          GPIO_PIN_0
#define DAC_MUTE_GPIO_Port   GPIOA
#define DAC_MUTE_Pin         GPIO_PIN_1

static void dac_cs_low(void)  { HAL_GPIO_WritePin(DAC_CS_GPIO_Port, DAC_CS_Pin, GPIO_PIN_RESET); }
static void dac_cs_high(void) { HAL_GPIO_WritePin(DAC_CS_GPIO_Port, DAC_CS_Pin, GPIO_PIN_SET); }

static HAL_StatusTypeDef pcm1795_write_reg(uint8_t reg, uint8_t value) {
    uint8_t frame[2];
    frame[0] = reg;
    frame[1] = value;
    dac_cs_low();
    HAL_StatusTypeDef st = HAL_SPI_Transmit(&hspi1, frame, sizeof(frame), HAL_MAX_DELAY);
    dac_cs_high();
    return st;
}

static void pcm1795_reset_sequence(void) {
    HAL_GPIO_WritePin(DAC_RST_GPIO_Port, DAC_RST_Pin, GPIO_PIN_RESET);
    HAL_Delay(10);
    HAL_GPIO_WritePin(DAC_RST_GPIO_Port, DAC_RST_Pin, GPIO_PIN_SET);
    HAL_Delay(10);
}

static void pcm1795_init(void) {
    dac_cs_high();
    HAL_GPIO_WritePin(DAC_MUTE_GPIO_Port, DAC_MUTE_Pin, GPIO_PIN_SET);
    pcm1795_reset_sequence();

    // TODO: Replace register addresses/values with the exact PCM1795 board mode.
    // Configure audio format, oversampling, de-emphasis, and mute control per PCM1795 datasheet.
    // pcm1795_write_reg(REGISTER_ADDR, REGISTER_VALUE);

    HAL_GPIO_WritePin(DAC_MUTE_GPIO_Port, DAC_MUTE_Pin, GPIO_PIN_RESET);
}

int main(void) {
    HAL_Init();
    SystemClock_Config();
    MX_GPIO_Init();
    MX_SPI1_Init();
    MX_I2S3_Init();

    pcm1795_init();

    // Example 16-bit stereo silence buffer. Replace with real PCM stream.
    uint16_t silence[128] = {0};

    while (1) {
        HAL_I2S_Transmit(&hi2s3, silence, 128, HAL_MAX_DELAY);
    }
}

Build & Flash Instructions

Create an STM32CubeIDE project for the exact STM32F407 board.
Enable one SPI peripheral in I2S master transmit mode for BCK/LRCK/DATA/MCLK.
Enable one SPI peripheral or GPIO bit-banged interface for PCM1795 control.
Map the GPIO labels above to the actual header pins used on the STM32F407 board.
Build and flash with ST-LINK or the board's onboard programmer.

TODO Before Hardware Bring-Up

Confirm exact STM32F407 board model and available I2S pins.
Confirm PCM1795 board pinout and whether MCLK is required.
Confirm PCM1795 register settings for I2S word length, sample rate, and analog output mode.

Platform & Toolchain
Pin Mapping
Example STM32 HAL Source Skeleton
Build & Flash Instructions
TODO Before Hardware Bring-Up