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I2S Audio pHAT

I2S Audio Interface for Raspberry Pi Zero


This is a Raspberry Pi Zero pHAT form-factor I2S audio interface board based on a Cirrus Logic (Wolfson) WM8731 audio codec. It provides line input, line output, headphones output, and includes an on-board microphone.

Micro 8088 Assembled Board

Hardware Documentation

Schematic and PCB Layout

Schematic - Version 3.0

PCB Layout - Version 3.0

Bill of Materials

I2S Audio pHAT project on - View and order all components except of the PCB.

I2S Audio pHAT project on OSH Park - View and order the PCB.

Component type Reference Description Quantity Possible sources and notes
PCB I2S Audio pHAT PCB - Version 3.0 1 Order from OSH Park
Integrated Circuit U1 WM8731, I2S audio codec, SSOP28 1 Mouser 238-WM8731SEDS/V
Integrated Circuit U2 TPS79333DBVR, LDO, SOT23-5 1 Mouser 595-TPS79333DBVR
Integrated Circuit U3 CAT24C32WI-GT3, I2C EEPROM, SOIC8 1 Mouser 698-CAT24C32WI-GT3
Crystal X1 12.288MHz, 3 mm x 5.3 mm 1 Mouser 717-7A-12.288MAAJ-T
Microphone MK1 9.7 mm, electret condenser microphone 1 Mouser 490-CMA-4544PF-W
Connector P1 3.5 mm audio jack, blue 1 Mouser 806-STX-31205B284C
Connector P2 3.5 mm audio jack, green 1 Mouser 806-STX-31205B577C
Connector P3 3.5 mm audio jack, black 1 Mouser 806-STX-3120-5B
Connector P4 20x2, 2.54 mm, socket 1 Mouser 517-929852-01-20-RB
Header JP1 2x1, 2.54mm, header 1 (optional) Mouser 855-M20-9990245
Capacitor C1, C2 22pF, 0603 2 Mouser 77-VJ0603A220JXACBC
Capacitor C3-C5 220pF, 0603 3 Mouser 77-VJ0603A221GXAPBC
Capacitor C6 0.01uF, 0603 1 Mouser 77-VJ0603Y103KXACBC
Capacitor C7-C12 0.1uF, 0603 6 Mouser 77-VJ0603Y104JXJPBC
Capacitor C13-C15 1uF, 5 mm, radial 3 Mouser 647-USW1H010MDD
Capacitor C16, C17 10uF, 5 mm, radial 2 Mouser 647-USW1H100MDD
Capacitor C18-C21 10uF, 0603 4 Mouser 81-GRM188R61A106KE9D
Capacitor C22, C23 220uF, 6.3 mm, radial 2 Mouser 647-USW0J221MDD
Resistor R1-R6 33 ohm, 0603 6 Mouser 603-RC0603FR-0733RL
Resistor R7, R8 100 ohm, 0603 2 Mouser 603-RC0603FR-07100RL
Resistor R9 330 ohm, 0603 1 Mouser 603-RC0603FR-07330RL
Resistor R10 680 ohm, 0603 1 Mouser 603-RC0603FR-07680RL
Resistor R11 1 kohm, 0603 1 Mouser 603-RC0603FR-071KL
Resistor R12, R13 3.9 kohm, 0603 2 Mouser 603-RC0603FR-073K9L
Resistor R14-R18 5.6 kohm, 0603 5 Mouser 603-RC0603FR-075K6L
Resistor R19-R22 47 kohm, 0603 4 Mouser 603-RC0603FR-0747KL

Software Documentation

Raspbian Configuration

Open /boot/config.txt in your favorite editor (nano, vi) as root, for example:

sudo nano /boot/config.txt

Comment out the dtparam=audio=on line:

# Enable audio (loads snd_bcm2835)

When using I2S Audio pHAT without ID EEPROM (see Raspberry Pi HAT ID EEPROM Programming section below), add the following lines:

# Enable WM8731 codec

Save the file and reboot the system.

Start alsamixer. If the I2S Audio pHAT is detected properly, it should show Card: snd_rpi_proto on the top left. Also use this opportunity to unmute Output Mixer HiFi control, otherwise the codec will not play any sound. To do so, use cursor keys to highlight that control, and then press the M key to unmute it.

When recording the sound, switch to Capture controls in alsamixer by pressing the F4 key. Next select the capture source: Line or Mic, and unmute it by pressing the Space key.

Now you can use your favorite application to play music or record sound. Enjoy!

Raspberry Pi HAT ID EEPROM Programming

The I2S Audio pHAT includes an ID EEPROM as specified by HAT requirements. This ID EEPROM allows Raspbian to automatically detect the I2S Audio pHAT, add it to the device tree, and load approprate overlays and kernel modules. Follow the instructions below to program the EEPROM.

Clone the Raspberry Pi hats repostory from GitHub:

git clone

Clone the I2S Audio pHAT repository from GitHub:

git clone

Build the eepromutils in the hats repository:

cd hats/eepromutils

Create the i2s_audio_phat.eep ID EEPROM image, using the eeprom_settings_i2s_audio_phat.txt file provided in the i2s_audio_phat repository:

./eepmake ../../i2s_audio_phat/eeprom_settings_i2s_audio_phat.txt i2s_audio_phat.eep /boot/overlays/rpi-proto.dtbo

Finally, flash the i2s_audio_phat.eep ID EEPROM image to the EEPROM. Make sure to close the JP1 jumper on the I2S Audio pHAT before writing the EEPROM, for example using male to male jumper wire, or otherwise the write will fail.

sudo ./ -w -f=i2s_audio_phat.eep -t=24c32


I2S Audio pHAT




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