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SimplePilot v2.14 — Wiring Reference

Companion to the SVG schematic: schematic_simplepilot_v2.14.svg

ESP32 Pin Assignments

ESP32 GPIO Function Direction Signal Type Connected To Notes
GPIO 21 I2C SDA I/O I2C (400kHz) ICM-20948 SDA ESP32 default I2C SDA. Needs 4.7kΩ pullup to 3V3 (often on module).
GPIO 22 I2C SCL Output I2C (400kHz) ICM-20948 SCL ESP32 default I2C SCL. Needs 4.7kΩ pullup to 3V3 (often on module).
GPIO 25 DAC Throttle Output DAC (0–255) Op-Amp input ESP32 DAC1. 0=0V, 255≈3.3V. Op-Amp (gain≈1.5×) boosts to 0.8V–4.2V for hall sensor.
GPIO 26 PWM_A Motor Output PWM (0–255) H-Bridge IN1 / PWM-A Right/Starboard direction. analogWrite() PWM.
GPIO 27 PWM_B Motor Output PWM (0–255) H-Bridge IN2 / PWM-B Left/Port direction. analogWrite() PWM.
GPIO 32 Pilot Joystick Input Analog (0–4095) Joystick VRy pot 12-bit ADC. Center≈1900. Left=0, Right=4095. Rudder axis.
GPIO 33 Pilot Switch Input Digital (PULLUP) SPST toggle switch LOW=ON (autopilot engage). Internal pullup — no external resistor needed.
GPIO 34 Cruise Joystick Input Analog (0–4095) Joystick VRx pot 12-bit ADC. Center≈1860. Input-only pin — no internal pullup available.
GPIO 4 Cruise Button Input Digital (PULLUP) Momentary N.O. button LOW=Pressed (toggle cruise). Internal pullup. Debounced in software (50ms).
GPIO 18 Pilot LED Output Digital LED + 330Ω → GND HIGH=ON when autopilot active.
GPIO 19 Cruise LED Output Digital LED + 330Ω → GND HIGH=ON when cruise control engaged.

Power Connections

Source Destination Voltage Notes
12V Battery (+) ESP32 VIN 5V (via onboard regulator) ESP32 DevKit has 5V→3.3V LDO. VIN accepts 5V–12V.
12V Battery (+) H-Bridge VCC 12V Motor power. Must be capable of 5–20A for actuator stall current.
12V Battery (+) Op-Amp VCC 12V (or 5V) Depends on op-amp choice. LM358 works on 5V–32V.
ESP32 3V3 ICM-20948 VCC 3.3V Both Pimoroni and SparkFun breakouts have onboard regulators.
ESP32 3V3 Joystick VCC 3.3V Powers both potentiometers. 3.3V = ADC full scale.
Common GND All components 0V CRITICAL: All grounds must be tied together. Star grounding recommended.

Component Details

ICM-20948 9-Axis IMU

Pin Connection Notes
VCC ESP32 3V3 3.3V logic. Module has onboard regulator if using 5V.
GND Common GND
SDA GPIO 21 I2C data. 4.7kΩ pullup to 3V3.
SCL GPIO 22 I2C clock. 4.7kΩ pullup to 3V3.
AD0 GND (Pimoroni) or VCC (SparkFun) Sets I2C address: AD0=GND → 0x68, AD0=VCC → 0x69. Set AD0_VAL in code accordingly.

I2C Address Configuration in Code:

#define AD0_VAL  0   // 0 = Pimoroni (0x68), 1 = SparkFun (0x69)

2-Axis Joystick (Potentiometer Module)

Pin Connection Notes
VCC ESP32 3V3 Must be 3.3V for ADC accuracy.
GND Common GND
VRx GPIO 34 Cruise/Throttle axis. Center ≈ 1860.
VRy GPIO 32 Pilot/Rudder axis. Center ≈ 1900.
SW (not connected) Joystick push-button. Not used in SimplePilot.

Calibration Values (adjust for your joystick):

#define JOYCRUISE_CENTER  1860   // VRx rest position
#define JOYPILOT_CENTER   1900   // VRy rest position

Switches

Pilot Toggle (SPST):

  GPIO33 ──┤ SWITCH ├── GND
            (closed = pilot ON)
  • Uses INPUT_PULLUP — switch connects GPIO33 to GND when closed.
  • LOW = autopilot engaged, HIGH = manual mode.

Cruise Button (Momentary N.O.):

  GPIO4 ──┤ BUTTON ├── GND
           (pressed = cruise toggle)
  • Uses INPUT_PULLUP — button connects GPIO4 to GND when pressed.
  • Software debounced (50ms delay after press).

H-Bridge Motor Driver (e.g., BTS7960 or VNH2SP30)

Pin Connection Notes
VCC 12V Battery Motor supply. Use heavy-gauge wire for current capacity.
GND Common GND Must share ground with ESP32.
PWM_A (IN1) GPIO 26 Right/Starboard direction PWM.
PWM_B (IN2) GPIO 27 Left/Port direction PWM.
EN (enable) 12V (or PWM) Must be HIGH for motor to run. Some drivers tie this to VCC.
OUT_A Actuator M+ Motor output A.
OUT_B Actuator M− Motor output B.

Motor Control Logic:

moveRight():  PWM_A = motorSpeed, PWM_B = 0    → Starboard
moveLeft():   PWM_A = 0,          PWM_B = motorSpeed → Port
StopActuator: PWM_A = 0,          PWM_B = 0    → Stopped

DAC + Op-Amp Throttle Circuit

                 ┌──────────┐
  GPIO25 (DAC) ──┤ +        ├───→ Hall Throttle Sensor
                 │  Op-Amp  │     (Outboard Engine)
  Rf/Ri div  ────┤ -        │    Gain ≈ 1.5×
                 └──────────┘
                      │
                    GND

Voltage Mapping:

DAC Value DAC Output Op-Amp Output Engine State
0 0.0V 0.0V ⚠ Sensor fault — never use!
41 ~0.53V ~0.8V Idle / tickover
215 ~2.78V ~4.2V Wide Open Throttle (WOT)
255 ~3.3V ~5.0V Beyond WOT (don't use)

⚠ IMPORTANT: Never set DAC below 41 (DACLOW). The hall-effect throttle sensor needs ~0.8V minimum to register idle. 0V looks like a disconnected sensor fault to the outboard.

Calibration Values:

#define DACLOW   41    // Idle: ~0.8V post-Op-Amp
#define DACHIGH  215   // WOT:  ~4.2V post-Op-Amp

LEDs

  GPIO18 ──┤ 330Ω ├───┤▶├─── GND    (Pilot LED — YELLOW)
  GPIO19 ──┤ 330Ω ├───┤▶├─── GND    (Cruise LED — GREEN)
  • 330Ω resistor limits current to ~10mA at 3.3V (standard LED).
  • Pilot LED: ON = autopilot active.
  • Cruise LED: ON = cruise control engaged.

Actuator Safety Limits

The linear actuator has physical endstops. The software enforces soft limits:

#define LIMIT_LEFT   500    // Actuator left limit (ADC counts)
#define LIMIT_RIGHT  3500   // Actuator right limit (ADC counts)

These constrain the joystick input range to prevent driving the actuator past its mechanical limits.

Key Constants Quick Reference

Constant Value Description
SAMPLE_HZ 25 Compass update rate (Hz)
DECLINATION_DEG 14.9° Magnetic declination (Possession Point)
KP 2.0 Proportional gain (autopilot)
KI 0.2 Integral gain (autopilot)
HEADING_HYSTERESIS 3° Don't steer if error < this
MAX_ERROR_DEG 45° Cap heading error for PI
MIN_AUTO_SPEED 80 Minimum PWM for actuator movement
RAMP_RATE 1.275 PWM ramp rate per ms (~200ms full ramp)
DACLOW 41 Throttle idle DAC value
DACHIGH 215 Throttle WOT DAC value

Wiring Checklist

  • ESP32 VIN connected to 12V battery (via fuse!)
  • All GND connections tied together (ESP32, H-Bridge, Op-Amp, IMU, Joystick)
  • ICM-20948 SDA → GPIO21, SCL → GPIO22 (check I2C pullups on module)
  • ICM-20948 AD0 pin matches AD0_VAL in code (0=Pimoroni/0x68, 1=SparkFun/0x69)
  • Joystick VRx → GPIO34, VRy → GPIO32, VCC → 3V3, GND → GND
  • Pilot toggle switch: GPIO33 ↔ GND (INPUT_PULLUP, LOW=ON)
  • Cruise momentary button: GPIO4 ↔ GND (INPUT_PULLUP, LOW=Pressed)
  • H-Bridge PWM_A ← GPIO26, PWM_B ← GPIO27
  • H-Bridge VCC ← 12V battery, EN ← 12V (or PWM)
  • Actuator M+/M− → H-Bridge motor outputs
  • DAC GPIO25 → Op-Amp input → Hall throttle sensor
  • Pilot LED: GPIO18 → 330Ω → LED → GND
  • Cruise LED: GPIO19 → 330Ω → LED → GND
  • 12V battery fused (recommended: 10A slow-blow for actuator circuit)
  • ESP32 powered via VIN (not 3V3 pin — onboard regulator needed)