A nightstand noise generator based on M5Stack Atom Echo and integrating with Home Assistant
firmware: drive external MAX98357A on G21/G26/G32
Now that the external amps are wired up and the audio chain is
validated end-to-end on a breadboard, switch the I2S driver off the
onboard NS4168 (G19 BCLK / G22 DOUT / G33 LRCK) and onto the planned
external pins (G26 BCLK / G21 DOUT / G32 LRCK). The onboard amp
receives no I2S now, so its tiny speaker stays silent regardless.
Renamed `make_onboard_i2s` → `make_i2s` since there's only one I2S
driver in this firmware. README updates: status table, removal of the
"prototype-only path" gotcha that's no longer relevant, and the pinout
cheat sheet rewritten around the new active pins (G19/G22/G33 listed
as reserved-but-driven-silent, since they still feed the onboard amp
internally — we just don't send them anything).
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
+23
-28
+11
-15
firmware/README.md
+11
-15
firmware/README.md
···
12
12
| --- | --- |
13
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| Cargo build + flash | ✅ working |
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| GPIO input (button G39) | ✅ working — debounced, active-low |
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| I2S TX (16-bit / 44.1 kHz / stereo, Philips) | ✅ working into onboard NS4168 |
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+
| I2S TX (16-bit / 44.1 kHz / stereo, Philips) | ✅ working into external MAX98357A |
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| Continuous pink noise generator (Paul Kellet IIR) | ✅ xorshift32 white → pink filter, volume-scaled |
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| Button state machine (short / long / double) | ✅ working |
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| NVS persistence (volume + direction + playing) | ✅ working |
···
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| WiFi | ✅ working — STA, hostname `nightstand-<mac_hex>`, auto-reconnect |
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| MQTT client + HA discovery | ✅ working — LWT, retained discovery on (re)connect, `cmd/play`/`cmd/volume`/`cmd/update` subscribed |
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| OTA updates | ✅ working — `esp_https_ota` chunked download with HA progress bar, two-slot rollback |
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| Hardware: external MAX98357A + 1314 speaker | ❌ amps in transit; using onboard for now |
23
+
| Hardware: external MAX98357A + GRS 3FR-4 speaker | ✅ assembled on breadboard |
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## Module layout
26
26
···
195
195
That's **`dout` before `ws`**, not `bclk → ws → dout` as you'd guess from reading "Bclk, Ws, Data" in audio convention. Getting them swapped produces:
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- "Static" instead of a tone (data on the LRCK line, clock on the data line)
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- A persistent quiet squeal during silence (WS clock ticking on the data input)
198
-
- The NS4168 amp running warm (sustained switching, no real audio output)
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+
- The amp running warm (sustained switching, no real audio output)
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199
200
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The compiler accepts both orderings since the pin types are generic. Always check the signature against the version of `esp-idf-hal` you're on. Symptom: garbage output where you'd expect tone.
201
201
···
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### 7. `esp_https_ota` rejects plain HTTP unless an opt-in flag is set
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Despite working fine at the protocol level, `esp_https_ota` validates the URL scheme and refuses plain HTTP unless `CONFIG_ESP_HTTPS_OTA_ALLOW_HTTP=y` is in sdkconfig. With the flag missing, `esp_https_ota_begin` returns immediately with an error and never opens a socket — webserver logs show no GET requests. The flag is set in `sdkconfig.defaults`.
225
-
226
-
### 8. The onboard NS4168 + tiny speaker is a prototype-only path
227
-
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We're using the I2S pins that drive the built-in amp (G19 BCLK, G22 DOUT, G33 LRCK) for hello-world. The plan ([signal-chain.md](../reference/signal-chain.md)) is to switch to an external MAX98357A on G21/G26/G32 once amps arrive. Don't run sustained white noise on the built-in speaker — short test bursts only. The thermal warning on this is real (we briefly demonstrated it via the swapped-pins bug above).
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## Layout
231
227
···
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└── .embuild/ # embuild-managed ESP-IDF clone (gitignored)
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```
250
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## Hardware-pinout cheat sheet (Atom Echo, prototype config)
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## Hardware-pinout cheat sheet (Atom Echo)
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| Pin | Function (this firmware) | Notes |
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250
| --- | --- | --- |
255
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| G39 | Button input | Active-low, on-board pull-up, input-only pin |
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| G19 | I2S BCLK → NS4168 | Onboard amp, prototype-only |
257
-
| G22 | I2S DOUT → NS4168 | Onboard amp data |
258
-
| G33 | I2S WS/LRCK → NS4168 | Onboard amp word select |
259
-
| G27 | SK6812 RGB LED data | Not used yet |
260
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| G26 | GROVE yellow / future I2S BCLK to MAX98357A | Free |
261
-
| G32 | GROVE white / future I2S WS to MAX98357A | Free |
262
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| G21 | Side header / future I2S DOUT to MAX98357A | Free |
252
+
| G26 | I2S BCLK → MAX98357A | GROVE yellow |
253
+
| G21 | I2S DOUT → MAX98357A | Side header |
254
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| G32 | I2S WS/LRCK → MAX98357A | GROVE white |
255
+
| G27 | SK6812 RGB LED data | On-board, top-face button cap |
256
+
| G19 | (reserved — onboard NS4168 BCLK) | Driven silent: no I2S routed here |
257
+
| G22 | (reserved — onboard NS4168 DOUT) | Driven silent: no I2S routed here |
258
+
| G33 | (reserved — onboard NS4168 LRCK / mic DATA) | Driven silent: no I2S routed here |
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| G25 | Side header / spare | Free |
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Authoritative pinout: [`../reference/atom-echo/pinmap.md`](../reference/atom-echo/pinmap.md).
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-7
firmware/src/audio.rs
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-7
firmware/src/audio.rs
···
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const FADE_DURATION_S: f32 = 0.7;
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const FADE_STEP_PER_SAMPLE: f32 = 100.0 / (FADE_DURATION_S * SAMPLE_RATE as f32);
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/// Construct the I2S driver for the onboard NS4168 amp.
39
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/// Construct the I2S driver for the external MAX98357A amp.
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///
41
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/// Pin assignment matches the M5Stack Atom Echo schematic:
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/// BCLK = G19, DOUT = G22, WS/LRCK = G33, no MCLK.
41
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/// Pin assignment per `reference/signal-chain.md`:
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/// BCLK = G26 (GROVE yellow), DOUT = G21 (side header),
43
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/// WS/LRCK = G32 (GROVE white), no MCLK.
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///
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/// **Argument order to `new_std_tx` is `(bclk, dout, mclk, ws)`** — not
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/// the audio-convention `(bclk, ws, dout)` you'd guess. Getting it wrong
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/// produces static instead of sound; see firmware/README.md gotcha #3.
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-
pub fn make_onboard_i2s(
48
+
pub fn make_i2s(
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i2s0: esp_idf_svc::hal::i2s::I2S0,
49
-
bclk: esp_idf_svc::hal::gpio::Gpio19,
50
-
dout: esp_idf_svc::hal::gpio::Gpio22,
51
-
ws: esp_idf_svc::hal::gpio::Gpio33,
50
+
bclk: esp_idf_svc::hal::gpio::Gpio26,
51
+
dout: esp_idf_svc::hal::gpio::Gpio21,
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+
ws: esp_idf_svc::hal::gpio::Gpio32,
52
53
) -> Result<I2sDriver<'static, I2sTx>> {
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let config = StdConfig::new(
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55
Config::default(),
+4
-6
firmware/src/main.rs
+4
-6
firmware/src/main.rs
···
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71
// will refresh this once it knows whether we landed online or offline.
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let _ = led_tx.send(LedSignal::Net(NetStatus::Connecting));
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// Audio task: I2S to the onboard NS4168 (prototype). Will move to the
75
-
// external MAX98357A on G21/G26/G32 once amps arrive.
76
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let i2s = audio::make_onboard_i2s(
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+
let i2s = audio::make_i2s(
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peripherals.i2s0,
78
-
pins.gpio19, // BCLK
79
-
pins.gpio22, // DOUT
80
-
pins.gpio33, // WS / LRCK
76
+
pins.gpio26, // BCLK
77
+
pins.gpio21, // DOUT
78
+
pins.gpio32, // WS / LRCK
81
79
)?;
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let _audio_handle = audio::spawn(
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i2s,