AeroAlign/hardware/schematics/sensor_node_wiring.md

# SkyLogic AeroAlign - Sensor Node Wiring Diagram

**Version**: 1.0.0
**Date**: 2026-01-22
**Target Hardware**: ESP32-C3/ESP32-S3 + MPU6050 + LiPo + TP4056

---

## Overview

This document describes the complete wiring schematic for both Master and Slave sensor nodes. Both nodes use identical wiring (Master additionally runs WiFi AP + web server in firmware).

---

## Component List (Per Node)

| Component | Part Number | Quantity | Function |
|-----------|-------------|----------|----------|
| ESP32-C3 DevKit | ESP32-C3-DevKitM-1 | 1 | Microcontroller |
| MPU6050 IMU | GY-521 module | 1 | 6-axis motion sensor |
| LiPo Battery | 1S 3.7V 250-400mAh | 1 | Power source |
| TP4056 Charger | USB-C variant | 1 | Battery charging |
| HT7333 LDO | 3.3V 250mA | 1 | Voltage regulator |
| 10kΩ Resistor | 1/4W carbon film | 2 | Voltage divider for battery ADC |
| JST Connector | 2-pin PH2.0 | 1 | Battery connector |
| USB-C Cable | 1m | 1 | Charging/flashing |

---

## Power Supply Wiring

```
LiPo Battery (3.7V nominal, 4.2V max, 3.0V min)
    │
    ├─► [+] TP4056 IN+  (Battery charging input)
    │       TP4056 IN-  [GND]
    │       TP4056 USB-C (for charging only)
    │
    └─► [+] HT7333 VIN  (3.0V - 4.2V input)
            HT7333 GND  [GND]
            HT7333 VOUT [3.3V] ─► ESP32-C3 3.3V pin
                                  MPU6050 VCC
```

**Notes**:
- TP4056 charges LiPo when USB-C connected (red LED: charging, blue LED: full)
- HT7333 regulates LiPo voltage to stable 3.3V for ESP32 and IMU
- ESP32-C3 DevKit has built-in USB-C for programming (separate from TP4056 charging USB-C)

---

## ESP32-C3 to MPU6050 (I2C) Wiring

```
ESP32-C3              MPU6050 (GY-521)
---------             ----------------
GPIO4 (SDA) ───────► SDA (I2C Data)
GPIO5 (SCL) ───────► SCL (I2C Clock)
3.3V        ───────► VCC
GND         ───────► GND
                     INT (not connected)
                     AD0 (GND for 0x68 address)
```

**I2C Configuration**:
- **Address**: 0x68 (default, AD0 pulled low)
- **Frequency**: 400kHz (fast mode)
- **Pull-ups**: Internal ESP32 pull-ups enabled (no external resistors needed)

**Alternative**: BNO055 IMU (for ±0.1° accuracy upgrade)
```
ESP32-C3              BNO055
---------             ------
GPIO4 (SDA) ───────► SDA
GPIO5 (SCL) ───────► SCL
3.3V        ───────► VIN
GND         ───────► GND
                     PS0 (GND for I2C mode)
                     PS1 (3.3V)
```

---

## Battery Monitoring (Voltage Divider)

```
LiPo+ (3.0V - 4.2V)
    │
    ▼
   10kΩ Resistor (R1)
    │
    ├────► ESP32-C3 GPIO0 (ADC1_CH0)
    │
    ▼
   10kΩ Resistor (R2)
    │
    └────► GND

Output Voltage = (LiPo Voltage) / 2
ESP32 ADC reads 0-1650mV (half of LiPo voltage)
```

**Calculation**:
```cpp
float adc_value = analogRead(GPIO0);  // 0-4095 (12-bit)
float voltage_at_adc = (adc_value / 4095.0) * 3.3;  // Convert to volts
float battery_voltage = voltage_at_adc * 2.0;  // Multiply by voltage divider ratio
uint8_t battery_percent = ((battery_voltage - 3.0) / (4.2 - 3.0)) * 100.0;
```

**Important**:
- R1 and R2 must be equal (10kΩ each) for 2:1 division
- ESP32-C3 ADC max input: 3.3V (do NOT exceed)
- LiPo max voltage 4.2V / 2 = 2.1V (safe margin)

---

## Status LED (Optional)

```
ESP32-C3 GPIO10 ───► [+] LED [-] ───► 220Ω Resistor ───► GND
```

**LED Indicators**:
- **Solid Blue**: WiFi AP active (Master only)
- **Slow Blink (1Hz)**: Normal operation, connected
- **Fast Blink (5Hz)**: Searching for Master (Slave only)
- **Red Blink (3×)**: Low battery (<20%)

---

## Complete Schematic (ASCII Art)

```
                    +──────────────────────────────────────+
                    │      LiPo Battery (1S 3.7V)         │
                    │         250-400mAh                   │
                    +──────────────────────────────────────+
                             │                  │
                             │+                 │-
                             │                  │
                    ┌────────┴────────┐         │
                    │   TP4056 Charger │         │
USB-C Charge ───────┤   (USB-C input)  │         │
                    │   OUT+       OUT-│         │
                    └─────┬────────────┴─────────┤
                          │+                    -│
                          │                      │
                    ┌─────┴──────────────────────┴─────┐
                    │   HT7333 LDO Regulator           │
                    │   VIN        GND        VOUT     │
                    └──────────────┬───────────┬───────┘
                                   │           │ 3.3V
                                   │           │
                     ┌─────────────┴───────────┴────────┐
                     │      ESP32-C3 DevKit             │
                     │                                  │
     USB-C Flash ────┤ USB-C                            │
                     │                                  │
                     │  GPIO4 (SDA) ──────┐             │
                     │  GPIO5 (SCL) ──────┤             │
                     │  GPIO0 (ADC) ──────┤             │
                     │  GPIO10 (LED) ─────┤             │
                     │  3.3V ─────────────┤             │
                     │  GND ──────────────┤             │
                     └────────────────────┼─────────────┘
                                          │
                                          │
                     ┌────────────────────┴─────────────┐
                     │   MPU6050 IMU (GY-521)           │
                     │                                  │
                     │   SDA ◄──────────────────────────┤
                     │   SCL ◄──────────────────────────┤
                     │   VCC ◄───── 3.3V ───────────────┤
                     │   GND ◄───── GND ────────────────┤
                     │   INT (not connected)            │
                     │   AD0 ◄───── GND (0x68 address)  │
                     └──────────────────────────────────┘

                         Battery Monitor (Voltage Divider)

                     LiPo+ ──┬── 10kΩ ──┬── 10kΩ ── GND
                             │          │
                             │          └──► GPIO0 (ADC)
                             │
                         (Read half voltage)
```

---

## Pin Assignment Summary

### ESP32-C3 GPIO Mapping

| GPIO Pin | Function | Connection | Notes |
|----------|----------|------------|-------|
| GPIO0 | ADC1_CH0 | Battery voltage divider midpoint | Read battery level |
| GPIO4 | I2C SDA | MPU6050 SDA | IMU data line |
| GPIO5 | I2C SCL | MPU6050 SCL | IMU clock line |
| GPIO10 | Digital Out | Status LED (optional) | Connection indicator |
| 3.3V | Power | HT7333 VOUT, MPU6050 VCC | Regulated power rail |
| GND | Ground | Common ground | All components share |
| USB-C | USB Serial | Flashing/debugging | Built-in on DevKit |

### MPU6050 (GY-521) Pinout

| Pin | Function | Connection | Notes |
|-----|----------|------------|-------|
| VCC | Power | ESP32 3.3V | 3.3V or 5V compatible |
| GND | Ground | Common GND | - |
| SDA | I2C Data | GPIO4 | Pull-up enabled internally |
| SCL | I2C Clock | GPIO5 | Pull-up enabled internally |
| INT | Interrupt | Not used | Future: motion detection |
| AD0 | Address Select | GND | Sets I2C address to 0x68 |

---

## Assembly Instructions

### Step 1: Solder HT7333 LDO

1. **Identify pins**: HT7333 (SOT-89 package)
   ```
   ┌───────┐
   │ HT7333│
   └┬─┬─┬──┘
    │ │ └── VOUT (3.3V output)
    │ └──── GND
    └────── VIN (3.0V-6.0V input)
   ```

2. Solder to TP4056 OUT+ (VIN) and OUT- (GND)
3. Connect VOUT to ESP32-C3 3.3V rail

### Step 2: Connect Battery

1. Solder JST connector to LiPo (red = +, black = -)
2. Connect to TP4056 BAT+ and BAT-
3. **Important**: Check polarity before connecting!

### Step 3: Wire I2C to MPU6050

1. Solder 4 wires (SDA, SCL, VCC, GND) from ESP32-C3 to MPU6050
2. Use 22AWG silicone wire (flexible, ~10cm length)
3. Test continuity with multimeter

### Step 4: Install Voltage Divider

1. Solder two 10kΩ resistors in series
2. Connect high end to LiPo+ (or TP4056 OUT+)
3. Connect midpoint to ESP32-C3 GPIO0
4. Connect low end to GND
5. Cover with heat shrink tubing

### Step 5: Test Power Supply

1. **Without ESP32 connected**: Measure HT7333 VOUT with multimeter
2. Expected: 3.25V-3.35V (3.3V ±50mV)
3. If correct, connect ESP32-C3 3.3V pin

### Step 6: Flash Firmware

1. Connect ESP32-C3 USB-C to computer
2. Flash Master or Slave firmware via PlatformIO
3. Open serial monitor (115200 baud)
4. Verify IMU initialization: "MPU6050 initialized (0x68)"

### Step 7: Calibrate IMU

1. Place sensor on flat, level surface
2. Power on, wait 10 seconds for stabilization
3. Web UI (Master) or serial output (Slave) should show ~0.0° pitch/roll

---

## Troubleshooting

### Problem: ESP32 won't power on

**Check**:
- LiPo voltage (should be 3.7V-4.2V)
- HT7333 VOUT (should be 3.3V)
- TP4056 protection (may shut down if overcharged/over-discharged)

**Solution**: Charge LiPo via TP4056 USB-C

### Problem: I2C not detected (MPU6050 not found)

**Check**:
- Wiring: SDA to GPIO4, SCL to GPIO5
- I2C address: Run I2C scanner (should show 0x68)
- Pull-ups: Enable internal pull-ups in firmware

**Solution**: Verify connections, re-solder if cold joints

### Problem: Battery percentage reads 0% or 255%

**Check**:
- Voltage divider wiring (two 10kΩ resistors in series)
- ADC pin (GPIO0) connection to midpoint
- ADC code calibration (3.3V ADC reference)

**Solution**: Measure voltage at GPIO0 with multimeter (should be LiPo voltage / 2)

### Problem: IMU angles drift over time

**Check**:
- Complementary filter alpha (should be 0.98)
- IMU temperature (MPU6050 sensitive to >15°C delta from calibration)
- Vibration isolation (sensor should be firmly mounted)

**Solution**: Recalibrate at operating temperature, increase filter alpha to 0.99

---

## Safety Warnings

⚠️ **LiPo Battery Safety**:
- Never short-circuit LiPo terminals (fire/explosion risk)
- Do not charge above 4.2V (TP4056 prevents this)
- Do not discharge below 3.0V (TP4056 prevents this)
- Store at 50-60% charge (3.7V-3.8V) if unused >1 week
- Dispose of damaged/swollen batteries at hazardous waste facility

⚠️ **Soldering Safety**:
- Use 300-350°C iron temperature (too hot damages components)
- Solder in ventilated area (avoid flux fumes)
- Do not touch soldering iron tip (obvious, but critical)

⚠️ **ESD Protection**:
- ESP32-C3 and MPU6050 are ESD-sensitive
- Touch grounded metal before handling (discharge static)
- Avoid working on carpets or synthetic fabrics

---

## Bill of Materials (Per Node)

See `hardware/schematics/bom.csv` for complete BOM with Amazon ASINs and pricing.

**Quick Summary**:
- ESP32-C3 DevKit: $6.50
- MPU6050 IMU: $4.50
- LiPo Battery (400mAh): $8.00
- TP4056 Charger: $1.50
- HT7333 LDO: $0.80
- Resistors, wire, connectors: $2.00
- **Total per node**: ~$23.30

---

## Revision History

| Version | Date | Changes |
|---------|------|---------|
| 1.0.0 | 2026-01-22 | Initial wiring diagram for MVP |

---

*SkyLogic AeroAlign - Precision Grounded.*