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Tiny Engineer — hardware overview

Canonical hardware reference for the Tiny Engineer robot.

Firmware pin constants live in include/pins.h. Wiring topology lives in docs/wiring/Tiny Engineer.drawio.png.

Conflict order: firmware GPIO numbers → wiring PNG connections → this docs/hardware/ set.

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.

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 SCK"| OLED
  ESP -->|"GP2 BCLK / GP3 LRC / GP4 DIN"| MAXVIN
  PCA -->|"PWM"| SERVOS
Loading

Speaker SPK+/SPK- are not on the PNG. See 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 Part Qty
Controller Waveshare ESP32-C3-Zero 1
Servo PWM Adafruit PCA9685 16-channel driver 1
Actuators PowerHD HD-1370A analog micro servo 5
Audio amp MAX98357A I2S class-D (mono) 1
Speaker 8 Ω / 1 W mono 1
Display 0.91" 128×32 OLED, SSD1306, I2C 1
Robot USB Adafruit 5993 USB-C breakout (power + data) 1

Full inventory: components.md.

Communication buses

Bus ESP32 pins Devices
I2C GP0/SDA, GP1/SCL (OLED pad SCK) PCA9685 0x40, SSD1306 0x3C
I2S GP2/BCLK, GP3/LRC, GP4/DIN MAX98357A
Servo PWM (none on ESP32) PCA9685 channels 0–4 @ 50 Hz
USB Adafruit 5993 (VBUS/GND + D+/D− → GP19/GP18) Power, flash, serial CDC

Details: interfaces.md, pinout.md.

Power architecture

Single nominal +5V supply via the Adafruit 5993. ESP32 onboard LDO makes 3V3 for logic only. PCA9685 V+ (servos) is electrically separate from PCA9685 VCC (logic).

Adafruit 5993 CC resistors request 5 V / up to ~1.5 A. Five stalled servos alone can approach that. Prefer a 5 V / ≥2 A source with margin.

Details: power.md.

Documentation map

File Contents
components.md Inventory, voltages, limits
pinout.md GPIO map + allocation rules
wiring.md Every electrical connection
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

Existing schematic sketch (not a substitute for the tables here): docs/wiring/Tiny Engineer.drawio / PNG.

Source-of-truth order

  1. Repository firmware / include/pins.h
  2. This docs/hardware/ set and docs/wiring/
  3. Component datasheets