Using a Digital-to-Analog Converter (DAC)

Welcome to the DAC Lab

Monty waving welcome Your Pico speaks in digital numbers — ones and zeros. But speakers need a smooth, changing voltage to make sound. A DAC is the translator that turns digital numbers into smooth audio signals. Let's build something amazing!

What Is a DAC?

A Digital-to-Analog Converter (DAC) takes a stream of digital numbers and turns them into a smoothly changing voltage. That smooth voltage is what you feed into a speaker or amplifier to produce sound.

Without a DAC:

The Pico can only output a square wave (buzzer-style tones).
Audio quality is harsh and robotic.

With a DAC:

The Pico outputs real audio waveforms.
You can play music, speech, and sound effects at CD quality.

Key Idea

Monty thinking Think of the DAC like a very fast water faucet. The Pico tells it a number (say, 127 out of 255), and the DAC opens the faucet to exactly halfway. Change the number thousands of times per second, and you get smooth audio.

Types of DAC Connections

There are two common ways to add a DAC to a MicroPython project:

1. I2S DAC Modules

The most popular approach. The Pico sends audio data over the Inter-IC Sound (I2S) bus to a DAC chip. The chip converts the digital data into an analog signal.

Popular I2S DAC modules:

Module	Max Power	Notes
MAX98357A	3 W mono	Has a built-in amplifier — connect speaker directly
PCM5102A	headphone level	High-quality stereo, no amplifier
UDA1334A	headphone level	Stereo with I2S and optical input

The MAX98357A is the best choice for beginners because it combines the DAC and a speaker amplifier in one board. No extra amplifier needed.

2. Pulse-Width Modulation (PWM) as a Rough DAC

The Pico does not have a true analog output pin. But you can use PWM with a low-pass filter (a resistor and capacitor) to create a rough version of analog audio. This works for speech playback and simple sound effects but is not good enough for music.

Wiring a MAX98357A to the Pico

MAX98357A Pin	Pico Pin	Signal
VIN	3V3 (pin 36)	3.3 V power
GND	GND	Ground
BCLK	GP10	I2S bit clock (SCK)
LRC	GP11	I2S word select (WS)
DIN	GP9	I2S serial data (SD)
+ (speaker)	Speaker +	Speaker positive terminal
− (speaker)	Speaker −	Speaker negative terminal

Connect a small 4 Ω or 8 Ω speaker (0.5 W to 3 W) to the + and − output terminals on the MAX98357A module.

Watch Out!

Monty warning Never connect a speaker directly to a GPIO pin. The GPIO pin can only supply about 3 mA — not nearly enough to drive a speaker. Always use an amplifier like the MAX98357A between the Pico and the speaker.

Sample Program: Play a Sine Wave

This program generates a 440 Hz sine wave (the note A4) and plays it through a MAX98357A. A sine wave is the smoothest possible wave shape — it sounds like a pure, clean tone.

from machine import I2S, Pin   # import I2S and Pin classes
import math                     # import math for the sine function

# I2S pin numbers for the MAX98357A
SCK_PIN = 10                    # bit clock
WS_PIN  = 11                    # word select
SD_PIN  = 9                     # serial data output

# Set up the I2S transmitter
audio_out = I2S(
    0,                          # use I2S peripheral 0
    sck=Pin(SCK_PIN),           # connect the bit clock
    ws=Pin(WS_PIN),             # connect the word select
    sd=Pin(SD_PIN),             # connect the serial data
    mode=I2S.TX,                # TX = transmit (play audio)
    bits=16,                    # 16-bit audio samples
    format=I2S.MONO,            # single channel
    rate=22050,                 # 22,050 samples per second
    ibuf=10000                  # internal buffer: 10,000 bytes
)

SAMPLE_RATE = 22050             # must match the rate above
FREQUENCY   = 440              # Hz — the note A4 (concert A)
DURATION    = 3                 # play for 3 seconds
AMPLITUDE   = 30000            # volume — max is 32767 for 16-bit audio

# Calculate how many samples fit in one full cycle of the sine wave
samples_per_cycle = SAMPLE_RATE // FREQUENCY
# Create a buffer to hold one complete cycle
one_cycle = bytearray(samples_per_cycle * 2)  # 2 bytes per 16-bit sample

# Fill the buffer with one cycle of a sine wave
for i in range(samples_per_cycle):
    # Calculate the sine value for this sample position
    sample = int(AMPLITUDE * math.sin(2 * math.pi * i / samples_per_cycle))
    # Store the sample as two bytes (little-endian format)
    one_cycle[i * 2]     = sample & 0xFF         # low byte
    one_cycle[i * 2 + 1] = (sample >> 8) & 0xFF  # high byte

# Play the sine wave for DURATION seconds
total_bytes = SAMPLE_RATE * DURATION * 2         # total bytes to send
bytes_written = 0
while bytes_written < total_bytes:
    audio_out.write(one_cycle)                   # send one cycle of audio
    bytes_written += len(one_cycle)

audio_out.deinit()             # release the I2S hardware when done

What Each Line Does

Line	Purpose
`I2S(0, mode=I2S.TX, ...)`	Sets up I2S transmitter on peripheral 0
`bits=16`	16-bit audio samples (standard CD quality)
`format=I2S.MONO`	Single audio channel
`rate=22050`	22,050 samples per second
`math.sin(...)`	Calculates the sine wave value at each sample point
`audio_out.write(one_cycle)`	Sends the audio data to the DAC over I2S

Monty's Tip

Monty giving a tip Change FREQUENCY = 440 to other values to play different musical notes. For example, 262 Hz is Middle C, 494 Hz is B4, and 523 Hz is C5.

Great Work!

Monty celebrating You have connected a real DAC and generated an audio signal from scratch! Next, try playing a WAV file from the Pico's flash storage using the Playing Audio Files lab.