Buyers: start at shopping.md. The default build has the PCA9685, the MAX98357A, and USB-C on the main control board. This page is the electrical spec for those chips and the plug-in modules (ESP32, servos, OLED, speaker). Breakout SKUs are the advanced path — wiring.md.
Selected hardware only. Substituting a part means updating this file, pinout.md, and either the board design or wiring.md. Servo model may be any preset in servos.json if the printed parts match — parametric design.
Constants cited below match include/pins.h.
| Part | Link |
|---|---|
| Waveshare ESP32-C3-Zero | https://docs.waveshare.com/ESP32-C3-Zero |
| Adafruit PCA9685 breakout (advanced path) | https://www.adafruit.com/product/815 |
| Tower Pro SG90 (or equivalent) | Widely available hobby servo — no single canonical SKU |
| Feetech FS0307 | See vendor listing for FS0307 analog micro |
| EMAX ES9051 | See vendor listing for ES9051 analog micro |
| PowerHD HD-1370A (backward compatibility) | https://www.chd.hk/Product_Detail.aspx?id=30 |
| MAX98357A breakout (advanced path) | https://www.aliexpress.us/item/3256805196806369.html |
| Adafruit Mini Oval Speaker - 8 Ohm 1 Watt | https://www.adafruit.com/product/3923 |
| Waveshare 0.91inch OLED Module | https://www.waveshare.com/0.91inch-oled-module.htm |
| Adafruit 5993 USB-C breakout (advanced path) | https://www.adafruit.com/product/5993 |
| Field | Value |
|---|---|
| Exact model | Waveshare ESP32-C3-Zero (ESP32-C3FH4) |
| Quantity | 1 |
| Purpose | Main controller: I2C, I2S, USB CDC, Wi-Fi, onboard RGB |
| Operating voltage | GPIO 3.3 V. External power on the 5V pad: 3.7–6 V (robot uses the +5V rail) |
| Logic | 3.3 V only — do not drive 5 V into GPIO |
| Radio | Wi-Fi 2.4 GHz (product use). BLE present on silicon but out of scope |
| USB | Native USB on GPIO18/19 — reached via the main control board USB-C (onboard USB-C unused when assembled). Advanced path: Adafruit 5993 — wiring.md |
| Flash | 4 MB stacked flash on GPIO12–GPIO17 (those GPIOs are not exposed) |
| Onboard RGB | WS2812 on GPIO10 |
| Firmware notes | Boot: dim green status. Animations: white (typing/reading/thinking/talking/welcome/ring/wakeup), pulsing red (attention/error/dead), solid red (abort), off (idle/sleep). 1 s fade between non-pulse states. Fatal init errors: hang and blink red (1 = PCA9685, 2 = I2S). See blink codes and docs/api.md |
| BOOT | Button / strapping on GPIO9 |
| RESET | Separate RESET button (CHIP_EN), not a GPIO |
| UART0 silkscreen | TX = GPIO21, RX = GPIO20 |
| USB D− / D+ | GPIO18 / GPIO19 (native USB) |
| 3V3 regulator | Onboard LDO (Waveshare: ME6217C33M5G). For logic loads only |
| Important pins | See pinout.md |
| Limits | Do not power servos from 3V3. Do not cover the ceramic antenna with metal, PCB, or plastic. |
| Firmware note | PlatformIO board = esp32-c3-devkitm-1 is a build target, not the physical module. Physical board is C3-Zero. |
| Field | Value |
|---|---|
| Exact model | PCA9685 on the main control board. Advanced path: Adafruit 16-Channel 12-bit PWM/Servo Driver breakout |
| Quantity | 1 |
| Purpose | Independent 50 Hz servo PWM so ESP32 timing is not the PWM source |
| Operating voltage | VCC (logic): 3.3 V from ESP32 3V3. V+ (servos): +5V rail |
| Interface | I2C |
| Address | 0x40 (PCA9685_ADDRESS in firmware). A0–A5 pads can change this |
| PWM | 12-bit, firmware setPWMFreq(50) |
| Important pins | As drawn: 5V (servo-rail in), V+ (to servo 5V), VCC (3V3 logic), GND, SDA, SCL, PWM, OE (GP5, active LOW) |
| Channels used | 0–4 (five servos). 5–15 unused |
| Limits | V+ and VCC must stay separate. Do not jumper servo power onto logic VCC on this robot |
| Firmware note | Detection at 0x40 is a hard fail in the bring-up test |
Five analog micro servos drive the joints (Head / Neck / L hand / R hand / Body — robot-movement.md). Buy five of one model. Print the matching parts/{servo_id}/3mf/ folder. Which size to pick: parametric design.
Shared for every preset:
| Field | Value |
|---|---|
| Quantity | 5 (one model) |
| Operating voltage | Robot: +5V via PCA9685 V+ |
| Interface | Analog PWM, ~50 Hz. Signal is 3.3 V from PCA9685 — acceptable for this servo class |
| Pulse | Neutral ~1500 µs. Firmware window 800–2200 µs (SERVO_MIN_US / SERVO_MAX_US) |
| Important pins | SIG, +5V, GND (JR-style 3-wire) |
Warning
Never power the servos from the ESP32 3.3 V regulator.
Firmware uses per-servo safe ranges in include/servos.h (SERVO_SPECS). Tune after assembly if needed. Do not command full 0–180° / 800–2200 µs on the assembled robot. See servos.md.
Easiest to buy. Larger body → larger printed robot; electronics are easier to fit in the desk.
| Field | Value |
|---|---|
| Exact model | Tower Pro SG90 analog micro (or equivalent 9 g class) |
servo_id |
sg90 |
| Size | Larger than FS0307 / ES9051 / HD-1370A — see servos.json |
Print 3d_models/parts/sg90/3mf/.
More compact. Use this if you want a smaller robot that looks tighter on the desk.
| Field | Value |
|---|---|
| Exact model | Feetech FS0307 analog micro servo |
servo_id |
fs0307 |
Print 3d_models/parts/fs0307/3mf/.
Compact — similar footprint to FS0307, slightly taller body.
| Field | Value |
|---|---|
| Exact model | EMAX ES9051 analog micro servo |
servo_id |
es9051 |
Print 3d_models/parts/es9051/3mf/.
Still supported. Not the pick for a new build.
Print 3d_models/parts/hd1370a/3mf/.
| Field | Value |
|---|---|
| Exact model | PowerHD HD-1370A analog micro servo |
servo_id |
hd1370a |
| Current (datasheet stall) | ~260 mA @ 4.8 V, ~320 mA @ 6.0 V |
| No-load current | ~110 mA @ 4.8 V, ~120 mA @ 6.0 V |
| Idle current | ~4 mA @ 4.8 V, ~5 mA @ 6.0 V |
| Torque / speed | 0.4 kg·cm / 0.12 s/60° @ 4.8 V; 0.6 kg·cm / 0.10 s/60° @ 6.0 V |
| Size / mass | ~20.2 × 8.5 × 17.6 mm, ~3.7 g |
| Limits | Manufacturer sheet also lists ~130° travel over 800–2200 µs, while many retailers say 0–180°. Treat 0–180° as nominal, not a mechanical guarantee. |
| Field | Value |
|---|---|
| Exact model | MAX98357A on the main control board (I2S in, speaker out). Advanced path: breakout module |
| Quantity | 1 |
| Purpose | Digital audio → mono speaker. ESP32 never drives the speaker as GPIO PWM |
| Operating voltage | Vin 2.5–5.5 V. Drawing: USB 5V → Vin |
| I2S logic | 3.3 V from ESP32 (compatible) |
| Interface | I2S: BCLK, WS/LRC, DIN. No MCLK |
| Sample rates | Chip: 8–96 kHz. Firmware: 22050 Hz, 16-bit, stereo slot mode |
| Output power (typical) | ~1.8 W into 8 Ω @ 5 V / 10% THD (datasheet-class figure) |
| Important pins | Vin, GND, BCLK, LRC, DIN, SPK+, SPK-. Board gain: solder jumper (board README). Breakout GAIN / SD left unwired (GAIN floating ≈ 9 dB, SD pulled up ≈ left channel) — wiring.md |
| Limits | Output is BTL. Do not connect SPK- to GND. Do not feed SPK+/SPK- into another amplifier. Do not drive the speaker from ESP32 GPIO |
Warning
MAX98357A SPK- is not ground.
| Field | Value |
|---|---|
| Exact model | Adafruit Mini Oval Speaker - 8 Ohm 1 Watt (8 Ω, 1 W mono) |
| Quantity | 1 |
| Purpose | Acoustic output |
| Operating voltage | Not a voltage-rail device — driven by MAX98357A BTL |
| Interface | Two terminals → SPK+ and SPK- |
| Limits | 1 W rated. Amp can theoretically exceed 1 W into 8 Ω at 5 V; keep firmware volume moderate. Never connect either terminal to GND |
Speaker wiring is not drawn on docs/wiring/Tiny Engineer.drawio. Electrical rule is still: speaker ↔ SPK+/SPK- only.
| Field | Value |
|---|---|
| Exact model | Waveshare 0.91inch OLED Module (SKU 14657). Driver SSD1306, 128×32, I2C |
| Quantity | 1 |
| Purpose | Status / test UI |
| Operating voltage | Module accepts 3.3 V / 5 V. Robot VCC from ESP32 3V3 (confirmed in docs/wiring) |
| Interface | I2C on the shared bus. Pads VCC, GND, SDA, SCL |
| Address | 0x3C (OLED_ADDRESS in firmware). Alternate 0x3D exists on some modules if the ADDR jumper is changed — not used here |
| Resolution | 128×32 (OLED_WIDTH / OLED_HEIGHT) |
| Important pins | VCC, GND, SDA, SCL. Clock pad on this board is SCL. The wiring PNG may still label that net SCK (generic clone silkscreen) — same I2C clock, ESP32 GP1 |
| Firmware notes | SSD1306_SWITCHCAPVCC; rotation from oled_rotate_180 (setRotation(0) or 2). Missing OLED is non-fatal in the bring-up test |
| Limits | Robot wiring is 3V3. Do not hang this module on the servo +5V rail |
Default connector is on the main control board — power.md, main-control-board.md. Advanced path: Adafruit 5993 — wiring.md.
- Keep metal and dense plastic off the ESP32 ceramic antenna area.
- Servo horns and end stops: start from
SERVO_SPECSininclude/servos.h; tune after installation if needed. Assembled motion stays inside the saved min/max. - GPIO18/19 are native USB via the main control board USB-C (or the 5993 on the advanced path). Leave them assigned while using USB CDC for flash/serial.