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Wiring

Source of truth for what is connected to what: docs/wiring/Tiny Engineer.drawio.png (.drawio).

Firmware GPIO numbers: include/pins.h / pinout.md. Diagram labels pads GP0…GP21; those are the same pins as GPIO0…GPIO21.

Diagram colour: red = 5 V, blue = GND, thin wires = signals.

Pin names as drawn

Diagram label Same net / meaning
USB 5V +5V rail (Adafruit 5993 VBUS)
USB GND Common GND
USB D− / D+ 5993 data → ESP32 GP18 / GP19 (may be omitted on PNG)
ESP32 GP0 GPIO0, I2C SDA
ESP32 GP1 GPIO1, I2C SCL
ESP32 GP2 GPIO2, I2S BCLK
ESP32 GP3 GPIO3, I2S WS/LRC
ESP32 GP4 GPIO4, I2S DIN
PCA9685 5V Servo-power input from USB 5V
PCA9685 V+ Servo-power output to servo 5V
PCA9685 VCC Logic 3V3
OLED SCK I2C SCL
MAX98357A Vin Amp +5V (VIN)
MAX98357A LRC WS/LRC

On Adafruit PCA9685, header/terminal V+ is normally the same servo rail as the diagram’s PCA9685 5V pad. Do not treat PCA9685 5V as VCC.

Connection table (as drawn)

From Pin To Pin Purpose
USB (5993) 5V / VBUS ESP32-C3-Zero 5V Board 5 V in
USB (5993) 5V / VBUS PCA9685 5V Servo-rail in
USB (5993) 5V / VBUS MAX98357A Vin Amp power
USB (5993) GND ESP32-C3-Zero GND Common ground
USB (5993) GND PCA9685 GND (logic/header side) Common ground
USB (5993) GND OLED GND Common ground
USB (5993) GND MAX98357A GND Common ground
USB (5993) D− ESP32-C3-Zero GP18 Native USB D− (flash / CDC)
USB (5993) D+ ESP32-C3-Zero GP19 Native USB D+ (flash / CDC)
ESP32-C3-Zero 3V3 PCA9685 VCC PCA9685 logic
ESP32-C3-Zero 3V3 OLED VCC OLED power
ESP32-C3-Zero GP0 PCA9685 SDA I2C data
ESP32-C3-Zero GP0 OLED SDA I2C data (shared)
ESP32-C3-Zero GP1 PCA9685 SCL I2C clock
ESP32-C3-Zero GP1 OLED SCK I2C clock (shared; module silkscreen SCK)
ESP32-C3-Zero GP2 MAX98357A BCLK I2S bit clock
ESP32-C3-Zero GP3 MAX98357A LRC I2S word select
ESP32-C3-Zero GP4 MAX98357A DIN I2S data
ESP32-C3-Zero GP5 PCA9685 OE Optional output enable (see interfaces.md)
PCA9685 PWM Servo SIG Servo PWM
PCA9685 V+ Servo 5V Servo power
PCA9685 GND (servo side) Servo GND Servo ground

All modules must share a common ground. USB GND is the star in the drawing (ESP32, PCA9685 header, OLED, MAX98357A). Servo GND returns through PCA9685 servo-side GND, which is the same ground net.

Warning

Never power the servos from the ESP32 3.3 V regulator. Diagram: servo 5V ← PCA9685 V+; PCA9685 VCC ← ESP32 3V3 only.

Power (as drawn)

USB 5V
  → ESP32 5V
  → PCA9685 5V
  → MAX98357A Vin

PCA9685 V+
  → Servo 5V

ESP32 3V3
  → PCA9685 VCC
  → OLED VCC

USB GND
  → ESP32 GND
  → PCA9685 GND (header)
  → OLED GND
  → MAX98357A GND

PCA9685 GND (servo header)
  → Servo GND

USB block in the drawing is the Adafruit 5993 — robot power (VBUS/GND) and, when wired, programming (D+/D− → GP19/GP18). The PNG may show only 5V/GND; data wires are required for the single-USB design. See interfaces.md.

I2C (as drawn)

Shared bus:

  • ESP32 GP0 → PCA9685 SDA and OLED SDA
  • ESP32 GP1 → PCA9685 SCL and OLED SCK

Addresses (firmware, not on the drawing): PCA9685 0x40, OLED 0x3C. See interfaces.md.

I2S (as drawn)

  • ESP32 GP2 → MAX98357A BCLK
  • ESP32 GP3 → MAX98357A LRC
  • ESP32 GP4 → MAX98357A DIN
  • USB 5V → MAX98357A Vin
  • USB GND → MAX98357A GND

Drawn MAX98357A pads: Vin, GND, BCLK, LRC, DIN only.

PCA9685 → servo (as drawn)

One generic Servo block:

Servo PCA9685
SIG PWM
5V V+
GND GND

Firmware drives channels 0–4 (SERVO_CHANNELS). The drawing does not number the PWM header. Channel → joint: robot-movement.md / include/servos.h.

Pads drawn with no wires

ESP32-C3-Zero, unused in the PNG:

GP6, GP7, GP8, GP9, GP10, GP20, GP21

GP5 = optional PCA9685 OE (not in PNG). GP9 = BOOT, GP10 = onboard WS2812. GP18/GP19 = native USB — wire from 5993 D−/D+ even if the base PNG omits them. See pinout.md.

PCA9685 OE optional on GP5 — not drawn on base PNG. MAX98357A GAIN / SD not wired (breakout defaults). SPK+ / SPK- not drawn.

Not on the drawing

Still part of the selected hardware; do not invent extra ESP32 GPIO for them.

Item Rule
Speaker Terminals → MAX98357A SPK+ and SPK- only
4 extra HD-1370A Same 3-wire pattern as the drawn servo, on PCA9685 PWM 0–4
Adafruit 5993 D+/D− Wire to ESP32 GP19 / GP18 for flash and CDC (single-USB design)
MAX98357A GAIN / SD Not wired; leave breakout defaults

Warning

MAX98357A output is BTL. SPK- is not ground. Never tie SPK- or SPK+ to GND. Never drive the speaker from ESP32 GPIO.

USB connector (single)

Connector Role
Adafruit 5993 Only robot USB-C: VBUS/GND (power) + D+/D− → GP19/GP18 (flash / serial CDC)
ESP32-C3-Zero onboard USB-C Leave unused when 5993 data is wired (avoids dual 5 V feed)

See interfaces.md, power.md.

Assembly checks

  1. Every GND in the PNG is one net (USB, ESP32, PCA9685 both sides, OLED, MAX98357A, servo).
  2. PCA9685 VCC ≈ 3.3 V, PCA9685 5V / V+ ≈ 5 V, those two nets not shorted.
  3. OLED clock wire lands on the pad labelled SCK.
  4. I2S is GP2/GP3/GP4 → BCLK/LRC/DIN, not swapped with I2C.
  5. Speaker (if fitted) is only SPK+/SPK-, which are not in the PNG.