esp-idf/examples/peripherals/i2s/i2s_basic/i2s_pdm/README.md

Supported Targets	ESP32	ESP32-C3	ESP32-S3

I2S Basic PDM Mode Example

(See the README.md file in the upper level 'examples' directory for more information about examples.)

This example is going to show how to use the PDM TX and RX mode.

How to Use Example

Hardware Required

General

• A development board with any one of ESP32, ESP32-C3 or ESP32-S3 SoC
• A USB cable for power supply and programming

PDM RX

• A PDM microphone whose sel pin is supposed to be pulled down, and connecting its clk pin to EXAMPLE_PDM_RX_CLK_IO, data pin to EXAMPLE_PDM_RX_DIN_IO.

┌───────────────────────┐               ┌──────────────────┐
│          ESP          │               │   PDM microphone │
│                       │   PDM clock   │                  │
│ EXAMPLE_PDM_RX_CLK_IO ├──────────────►│ CLK              │
│                       │   PDM data    │                  │
│ EXAMPLE_PDM_RX_DIN_IO │◄──────────────┤ DATA             │
│                       │               │                  │
│                       │         ┌─────┤ SEL              │
│                       │         │     │                  │
│                   GND ├─────────┴─────┤ GND              │
│                       │               │                  │
│                   VCC ├───────────────┤ VCC              │
└───────────────────────┘               └──────────────────┘

PDM TX

• An earphone or a speaker
• An audio power amplifier that can input PDM signal. If the power amplifier can only receive the analog signal without PDM clock, a low-pass passive or active filter is required to restore the PDM data wave into analog signal, before it is transmitted to the power amplifier.

MAX98358

Please refer to the Datasheet of MAX98358 for more details.

┌────────────────────────┐               ┌───────────────┐
│          ESP           │               │   MAX 98358   │
│                        │   PDM clock   │               │
│  EXAMPLE_PDM_TX_CLK_IO ├──────────────►│ CLK           │   ┌─────────┐
│                        │   PDM data    │               │   │ Speaker │
│ EXAMPLE_PDM_TX_DOUT_IO ├──────────────►│ DATA     OUTP ├───┤         │
│                        │               │               │   │         │
│                        │         ┌─────┤ SD_MODE  OUTN ├───┤         │
│                        │         │     │               │   │         │
│                    VCC ├─────────┴─────┤ VCC           │   └─────────┘
│                        │               │               │
│                    GND ├───────────────┤ GND           │
└────────────────────────┘               └───────────────┘

NS4150

Please refer to the NS4150 datasheet for more details.

┌────────────────────────┐                              ┌───────────────┐
│          ESP           │                              │    NS 4150    │
│                        │                              │               │
│  EXAMPLE_PDM_TX_CLK_IO │(No need to connect)          │ INN           │   ┌─────────┐
│                        │PDM data┌────────────────┐    │               │   │ Speaker │
│ EXAMPLE_PDM_TX_DOUT_IO ├────────┤ Low-pass Filter├───►│ INP       VoP ├───┤         │
│                        │        └────────────────┘    │               │   │         │
│                        │                          ┌───┤ CTRL      VoN ├───┤         │
│                        │                          │   │               │   │         │
│                    VCC ├──────────────────────────┴───┤ VCC           │   └─────────┘
│                        │                              │               │
│                    GND ├──────────────────────────────┤ GND           │
└────────────────────────┘                              └───────────────┘

Configure the Project

PDM can only works in simplex mode, you can select the PDM direction in the menu config, or just setting the macro EXAMPLE_PDM_DIR directly. Setting it to EXAMPLE_PDM_TX or EXAMPLE_PDM_RX can choose the PDM direction of this example. But currently ESP32-C3 does not support PDM RX mode.

Build and Flash

Build the project and flash it to the board, then run monitor tool to view serial output:

idf.py -p PORT build flash monitor

(To exit the serial monitor, type Ctrl-].)

See the Getting Started Guide for full steps to configure and use ESP-IDF to build projects.

Example Output

PDM TX

While EXAMPLE_PDM_DIR is set to EXAMPLE_PDM_TX, then you can see the following log:

I2S PDM TX example start
---------------------------
D (284) i2s_common: tx channel is registered on I2S0 successfully
D (294) i2s_common: DMA malloc info: dma_desc_num = 6, dma_desc_buf_size = dma_frame_num * slot_num * data_bit_width = 500
D (304) i2s_pdm: Clock division info: [sclk] 160000000 Hz [mdiv] 3 [mclk] 49152000 Hz [bdiv] 8 [bclk] 6144000 Hz
D (314) i2s_pdm: The tx channel on I2S0 has been initialized to PDM TX mode successfully
D (324) i2s_common: i2s tx channel enabled
Playing bass `twinkle twinkle little star`
Playing alto `twinkle twinkle little star`
Playing treble `twinkle twinkle little star`
...

You can hear the audio 'twinkle twinkle little star' in three tones if you connect a speaker to it.

PDM RX

While EXAMPLE_PDM_DIR is set to EXAMPLE_PDM_RX, but without connecting a PDM microphone, then you can see the following log:

I2S PDM RX example start
---------------------------
D (10) i2s_common: rx channel is registered on I2S0 successfully
D (10) i2s_common: DMA malloc info: dma_desc_num = 6, dma_desc_buf_size = dma_frame_num * slot_num * data_bit_width = 500
D (20) i2s_common: i2s rx channel enabled
Read Task: i2s read 2048 bytes
-----------------------------------
[0] -6595 [1] 0 [2] -29199 [3] -32768
[4] -30203 [5] -32156 [6] -30704 [7] -31348

Read Task: i2s read 2048 bytes
-----------------------------------
[0] -30935 [1] -30935 [2] -30935 [3] -30935
[4] -30935 [5] -30935 [6] -30935 [7] -30935

Read Task: i2s read 2048 bytes
-----------------------------------
[0] -30935 [1] -30935 [2] -30935 [3] -30935
[4] -30935 [5] -30935 [6] -30935 [7] -30935

And only if you connect a PDM microphone, you can see the data changes:

I2S PDM RX example start
---------------------------
D (10) i2s_common: rx channel is registered on I2S0 successfully
D (10) i2s_common: DMA malloc info: dma_desc_num = 6, dma_desc_buf_size = dma_frame_num * slot_num * data_bit_width = 500
D (20) i2s_common: i2s rx channel enabled
Read Task: i2s read 2048 bytes
-----------------------------------
[0] -3181 [1] 0 [2] -7194 [3] -24288
[4] -777 [5] 3650 [6] 109 [7] 571

Read Task: i2s read 2048 bytes
-----------------------------------
[0] 2391 [1] 2378 [2] 2397 [3] 2385
[4] 2399 [5] 2375 [6] 2401 [7] 2389

Troubleshooting

For any technical queries, please open an issue on GitHub. We will get back to you soon.