Skip to content

HARDWARE.md

Latest commit

 

History

History
137 lines (102 loc) · 3.65 KB

HARDWARE.md

File metadata and controls

137 lines (102 loc) · 3.65 KB

Hardware Setup

I2S Output (MAX98357A)

An I2S audio module is recommended for best audio quality and here is described the popular and low cost MAX98357A but you can use also other similar modules.

Wiring

Raspberry Pi Pico          MAX98357A
─────────────────          ─────────
GP14 (I2S BCK)      →      BCK
GP15 (I2S WS/LRCLK) →      LRC
GP16 (I2S DATA)     →      DIN
3.3V                →      VIN
GND                 →      GND
                           SD → See below

SD Pin (Shutdown/Mode)

The SD pin controls both shutdown and mono/stereo mode:

  • GND - Shutdown (muted)
  • ~1.0V - Audio Unmuted and Mono output (left + right mixed)
  • 3.3V - Stereo output

So if you want to control by program the mute/unmute function you can make this simple circuit using in the same time the "mono" mode because when GPIO pin is high you have 1V on SD pin and when is low you "shutdown" the module.

Controlling SD pin

/***********************************************************
 I2SEnable()
 Enables the I2S audio  module
 ***********************************************************/
void I2SEnable() {
  digitalWrite(I2S_DS_PIN, HIGH);
  delay(5);
} // I2SEnable()

/***********************************************************
 I2SDisable()
 Disables the I2S audio module
 ***********************************************************/
void I2SDisable() {
  digitalWrite(I2S_DS_PIN, LOW);
  delay(5);
} // I2SDisable()

Configuration

In picosound_user_cfg.h:

#define USER_SND_OUT    OUT_I2S
#define USER_PIN_BCK    14
#define USER_PIN_WS     15
#define USER_PIN_DATA   16

Popular I2S modules:

  • Adafruit I2S 3W Class D Amplifier Breakout
  • SparkFun I2S Audio Breakout - MAX98357A
  • AZDelivery MAX98357A

PWM Output (Speaker/Amplifier)

While a simple prototype can be made using a resistor connected between the Pico's PWM pin and the "+" terminal of a small speaker with the "-" terminal connected to ground, a slightly better solution, both for sound quality and the integrity of the Pico itself, is to use a small NPN transistor.

This not only manages the current consumption better without excessively overloading the Pico, but also preserves its integrity by isolating it from the inductive load.

Wiring (NPN transistor + Passive Speaker)

PWM output with a NPN transistor

Note: Low volume. Use a Class D amplifier or a I2S module for better results.

Wiring (Class D Amplifier)

Pico GP17 → AMP IN
Pico GND  → AMP GND
AMP OUT   → Speaker

Popular amplifiers:

  • PAM8403 (3W stereo)
  • LM386 (1W mono)
  • TDA2030 (18W mono)

Configuration

In picosound_user_cfg.h:

#define USER_SND_OUT    OUT_PWM
#define USER_PIN_SPKR   17

Power Considerations

I2S (MAX98357A)

  • Current: ~10mA idle, ~500mA peak
  • Use separate 5V supply for high volume
  • Bypass capacitors: 100µF + 100nF near VIN

PWM

  • Current depends on amplifier
  • Pico GPIO max: 12mA
  • Always use amplifier for speakers >0.5W

Troubleshooting

No sound (I2S)

  1. Check wiring (BCK, WS, DIN)
  2. Verify SD pin voltage (~1V for mono)
  3. Check USER_SND_OUT == OUT_I2S in config
  4. Verify LittleFS mounted (for WAV files)

No sound (PWM)

  1. Check USER_SND_OUT == OUT_PWM
  2. Verify speaker/amplifier connection
  3. Increase volume with SetMasterVolume(100)

Crackling/Distortion

  1. Lower master volume
  2. Check power supply (needs clean 5V)
  3. Add decoupling capacitors
  4. Reduce simultaneous channels

Click during EEPROM write

Normal with I2S. Use hardware mute (see SD pin control above).