Numbers in, sound out

A speaker needs a voltage that moves

A speaker makes sound by moving its cone back and forth, hundreds or thousands of times a second, and it needs a voltage that swings with the sound and enough current to push the cone. A GPIO pin can only be HIGH or LOW, and it can supply only a little current.

So a sound has to be turned into a changing voltage, which is the job of a DAC (digital-to-analogue converter), and that voltage has to be made strong enough for a speaker, which is the job of an amplifier.

The chip does both

The NS4168 on the TK100 is both at once. The ESP32-S3 sends it a stream of numbers, one per sample; the chip turns each number into a position for the cone and drives the speaker there. A positive number pushes the cone out, a negative one pulls it in.

The numbers travel on I2S, a three-wire bus made for sound: a clock, a wire that says left or right, and a data wire. The ESP32-S3 makes all the clocks, and the chip only listens. Three wires, one channel takes them one at a time.

And one switch

The fourth signal pin, CTRL, switches the chip on. LOW or unconnected, it stays off, and a sketch that sends perfect numbers makes no sound at all. Every sketch in this book drives CTRL HIGH before it plays. The back of the board says so too: CTRL: HIGH->ON, LOW ->OFF.

What it needs from you

• An ESP32-S3. The builds use one; any board with an I2S peripheral and 3.3 V logic can drive it. An Arduino Uno cannot.
• A 3.3 V supply, from the 3V3 pin.
• A speaker. The kit's 4 Ω 3 W speaker plugs into the white socket.