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Tiny Engineer — hardware overview

Canonical hardware reference for the Tiny Engineer robot.

Firmware pin constants live in include/pins.h. The default build is the main control board (main-control-board.md). The advanced path wires separate breakouts (wiring.md + drawio) when you add modules the board does not support. Same nets and firmware.

Source of truth: firmware include/pins.h, then this docs/hardware/ set. Modular topology: docs/wiring/. PCB connectivity: board expected-nets.yml / netlist per pcb.md.

Audience Use this set for
Human Assembly, wiring, power, bring-up, debugging
Firmware agent Pin map, buses, voltages, servo PWM conventions, test sequence

Purpose

Small desktop robot with:

  • 5 analog micro servos (head, neck, hands, body — robot-movement.md)
  • I2C OLED status display
  • I2S speaker for tones and WAV playback
  • ESP32-C3 Wi-Fi for HTTP control and AI hooks

Firmware (src/main.cpp) is the robot application: Wi-Fi, settings, hardware tests, animations, and the JSON API.

Hardware architecture

One ESP32-C3 module owns all logic. Servo PWM is offloaded to a PCA9685 so pulse generation does not depend on ESP32 timing. Audio is I2S into a class-D amp. Display and servo driver share one I2C bus. On the default build those chips are on the main control board. The advanced path puts the same chips on breakouts — the diagram is the same either way.

flowchart TB
  USB["USB 5V / GND<br/>as drawn"]

  subgraph p5["5 V power domain"]
    ESP5["ESP32 5V"]
    PCA5["PCA9685 5V"]
    PCAVplus["PCA9685 V+"]
    MAXVIN["MAX98357A Vin"]
    SERVOS["Servo 5V"]
  end

  subgraph p33["3.3 V logic domain"]
    ESP["ESP32-C3-Zero"]
    PCA["PCA9685 VCC"]
    OLED["OLED VCC"]
  end

  USB -->|"5V"| ESP5
  USB -->|"5V"| PCA5
  USB -->|"5V"| MAXVIN
  PCA5 --> PCAVplus
  PCAVplus --> SERVOS
  ESP5 --> ESP
  ESP -->|"3V3"| PCA
  ESP -->|"3V3"| OLED
  ESP -->|"GP0 SDA / GP1 SCL"| PCA
  ESP -->|"GP0 SDA / GP1 SCL"| OLED
  ESP -->|"GP2 BCLK / GP3 LRC / GP4 DIN"| MAXVIN
  PCA -->|"PWM"| SERVOS
Loading

Speaker SPK+/SPK-: main-control-board.md. The modular PNG omits them — wiring.md.

Domain Voltage What lives there
Power rail +5V USB 5V → ESP32 5V, PCA9685 5V, MAX98357A Vin; PCA9685 V+ → servo 5V
Logic 3V3 ESP32 GPIO, PCA9685 VCC, OLED VCC, I2C, I2S
Ground GND Every module — common ground is mandatory

Warning

Never power the servos from the ESP32 3.3 V regulator.

Warning

MAX98357A SPK- is not ground. Speaker connects between SPK+ and SPK- only.

Major components

Role Main control board (default) Advanced breakouts Qty
Controller Waveshare ESP32-C3-Zero (plugs into board sockets) same 1
Servo PWM PCA9685 on PCB Adafruit PCA9685 breakout 1
Actuators Analog micro servos — Tower Pro SG90 recommended; Feetech FS0307 / EMAX ES9051 compact; PowerHD HD-1370A still supported same 5
Audio amp MAX98357A on PCB MAX98357A breakout 1
Speaker Adafruit Mini Oval Speaker - 8 Ohm 1 Watt same 1
Display Waveshare 0.91inch OLED Module (SSD1306, 128×32, I2C) same 1
Robot USB USB-C on PCB Adafruit 5993 USB-C breakout 1

Carts: shopping.md. Spec detail: components.md. Connect: main-control-board.md.

Communication buses

Bus ESP32 pins Devices
I2C GP0/SDA, GP1/SCL (Waveshare OLED SCL) PCA9685 0x40, SSD1306 0x3C
I2S GP2/BCLK, GP3/LRC, GP4/DIN MAX98357A
Servo PWM (none on ESP32) PCA9685 channels 0–4 @ 50 Hz
USB Board USB-C (VBUS/GND + D+/D− → GP19/GP18). Advanced path: 5993 — wiring.md Power, flash, serial CDC

Details: interfaces.md, pinout.md.

Power architecture

Single nominal +5V supply via the main control board USB-C. ESP32 onboard LDO makes 3V3 for logic only. PCA9685 V+ (servos) is electrically separate from PCA9685 VCC (logic). The advanced path brings 5 V in through an Adafruit 5993 — wiring.md.

Prefer a 5 V / ≥2 A source with margin. Details: power.md.

Documentation map

File Contents
../shopping.md Default cart; advanced extra modules
main-control-board.md Default connect: ESP32, OLED, servos, speaker
order-main-control-board.md Order the PCB / PCBA (any fab; JLCPCB walkthrough)
components.md Inventory, voltages, limits
pinout.md GPIO map + allocation rules
wiring.md Advanced: breakout harness
../3d/assembly-modular.md Advanced: mount breakouts in the desk
power.md Budget, brownout symptoms, single-USB policy
servos.md PWM, test limits, safe ranges
interfaces.md I2C / I2S / PWM / USB
testing.md Bring-up sequence, failures, what to check

Modular schematic sketch: docs/wiring/Tiny Engineer.drawio / PNG. KiCad: hardware/boards/; contribution rules: docs/pcb.md.

Source-of-truth order

  1. Repository firmware / include/pins.h
  2. This docs/hardware/ set; modular nets also in docs/wiring/; PCB nets via board expected-nets / netlist
  3. Component datasheets