Athena Instrument Panel — Hardware Wiring & Resistor Ladder Guide

This document provides a comprehensive technical reference for building and wiring the physical Athena Instrument Panel. It includes the complete Bill of Materials (BOM), the circuit design for reading a 12-position rotary switch via a single analog input pin, a system wiring diagram, and physical pinout assignments.

📦 1. Bill of Materials (BOM)

To build the hardware cockpit instrument panel, you need the following standard components:

Component	Quantity	Description	Interface / Type	Typical I2C Address / Pin
Microcontroller	1	Arduino Uno R3 or Arduino Nano V3.0	Central MCU	USB Serial (115200 bps)
LCD Display	1	16x2 Character LCD Screen	1602 LCD with PCF8574 Adapter	`0x27` (I2C)
Rotary Switch	1	1-Pole 12-Position (1P12T) Switch	Selector Switch (e.g., Lorlin CK1049)	Pin `A0` (Analog Ladder)
Magnetometer	1	LIS3MDL 3-Axis Digital Compass	Magnetic Field Telemetry	`0x1E` (I2C)
Inertial Sensor	1	LSM6DSOX 6DoF Accel / Gyro	Pitch & Heel Angle Telemetry	`0x6A` (I2C)
Power Switch	1	SPST Toggle Switch	Physical soft power toggle	Pin `D2` (Digital Input)
Backlight Switch	1	SPST Toggle Switch	Screen backlight control	Pin `D3` (Digital Input)
Resistors	11	10kΩ 1% Metal Film Resistors	Ladder dividers (in series)	Inter-switch terminal spacing
Resistor	1	10kΩ 1% Resistor	Pull-up resistor	Pin `A0` to `5V` (VCC)
Proto-board	1	Double-sided FR4 perfboard	Structural mounting / wiring hub	Ground / Power rails

⚙️ 2. Rotary Switch Resistor Ladder Circuit Design

Microcontrollers have limited digital GPIO pins. Wiring a 12-position rotary switch using 12 digital pins would consume nearly all available IO on an Arduino Uno.

By utilizing an analog resistor ladder, we map the 12 positions to distinct voltage levels. The microcontroller reads the voltage via a single analog input (A0) using its 10-bit Analog-to-Digital Converter (ADC) which maps 0V - 5V to values 0 - 1023.

Resistor Ladder Schematic

    5V (VCC)
       |
     [10k Pull-Up]
       |
  A0 --+--------------+---------------+---------------+ ... +
       |              |               |               |     |
    [ Pos 12 ]     [ Pos 11 ]      [ Pos 10 ]      [ Pos 9 ] [ Pos 1 ]
       |              |               |               |     |
      Direct        [10k]           [10k]           [10k]  Direct
     to VCC           |               |               |     |
                      +----[10k]------+----[10k]------+ ... +---- GND (0V)

Connect a 10kΩ resistor between each adjacent terminal on the rotary switch (11 resistors total in series).
Pin 1 of the switch is wired directly to GND (0V).
Pin 12 of the switch is wired directly to VCC (5V).
The Common Pole (center pin) of the switch is wired to Pin A0 on the Arduino.
Connect a 10kΩ Pull-Up resistor between A0 and VCC (5V).

Voltage Divider & 10-bit ADC Mapping Table

When the switch is toggled, it taps into the series resistor chain at different points, forming a voltage divider:

Switch Position	Total R to GND	Expected Voltage	ADC Target (0-1023)	Firmware Lower Boundary	Firmware Upper Boundary	Cockpit View Mapped
1	`0 Ω`	0.00 V	0	0	45	View 1: Tactical VMG
2	`10 kΩ`	0.45 V	93	46	139	View 2: Apparent Wind
3	`20 kΩ`	0.91 V	186	140	232	View 3: True Wind Heading
4	`30 kΩ`	1.36 V	279	233	325	View 4: Yacht Power Status
5	`40 kΩ`	1.82 V	372	326	418	View 5: Compass Heading
6	`50 kΩ`	2.27 V	465	419	511	View 6: Gyro Pitch & Roll
7	`60 kΩ`	2.73 V	558	512	604	View 7: Sail Configuration
8	`70 kΩ`	3.18 V	651	605	697	View 8: CRM Subscribers
9	`80 kΩ`	3.64 V	744	698	790	View 9: CRM Subscription Tier
10	`90 kΩ`	4.09 V	837	791	883	View 10: System Event Logs
11	`100 kΩ`	4.55 V	930	884	976	View 11: CAN-bus Status
12	`Infinite`	5.00 V	1023	977	1023	View 12: Settings Overview

🔌 3. Complete System Wiring Diagram

The instrument panel uses two physical buses:

The I2C Bus (sharing SCL and SDA lines with pull-ups) for telemetry modules and the screen display.
Discrete GPIO Pins for toggle switches and the analog ladder.

                               +-------------------+
                               |    Arduino Uno    |
                               |                   |
               +5V (VCC) ------| 5V                |
               GND ------------| GND               |
                               |                   |
               [I2C SDA] ------| A4 (SDA)          |
               [I2C SCL] ------| A5 (SCL)          |
                               |                   |
               Rotary Common --| A0 (Analog Input) |
               Power Switch ---| D2 (Digital Input)|
               Light Switch ---| D3 (Digital Input)|
                               +-------------------+
                                 |   |   |   |   |
     +---------------------------+   |   |   |   +--------------------------+
     |                               |   |   |                              |
     |     +-------------------------+   |   +------------------------+     |
     |     |                             |                            |     |
+----+-----+--------+         +----------+---------+         +--------+-----+----+
|   LCD Display     |         | LIS3MDL Compass    |         | LSM6DSOX Gyro     |
|   (Address 0x27)  |         | (Address 0x1E)     |         | (Address 0x6A)    |
|                   |         |                    |         |                   |
| VCC  GND  SDA  SCL|         | VCC  GND  SDA  SCL |         | VCC  GND  SDA  SCL|
+----+---+---+---+--+         +----+---+---+---+---+         +----+---+---+---+--+
     |   |   |   |                 |   |   |   |                  |   |   |   |
     +---+---+---+-----------------+---+---+---+------------------+---+---+---+
         |   |   |                     |   |   |                      |   |   |
        VCC GND SDA                   VCC GND SDA                    VCC GND SDA

[!IMPORTANT] Since the LiquidCrystal LCD Screen, LIS3MDL Compass, and LSM6DSOX Gyro scope all share the same I2C Bus, they must be wired in parallel. If using long cables (over 1 meter / 3 feet), connect 4.7kΩ Pull-Up Resistors between SDA and VCC, and between SCL and VCC to ensure signal integrity against high water moisture.

📌 4. Microcontroller Pinout Assignment

Here is the exact pinout mapping for wiring the components onto an Arduino Uno or Nano:

Arduino Pin	Component	Direction	Connection / Wiring Details
5V	System VCC	Output	Connected to LCD `VCC`, LIS3MDL `VIN`, LSM6DSOX `VIN`, and Rotary Switch Position 12.
GND	System GND	Output	Connected to LCD `GND`, LIS3MDL `GND`, LSM6DSOX `GND`, and Rotary Switch Position 1.
A0	Rotary Switch Common	Input (Analog)	Connected to center pole of Rotary Switch. Bridged to `5V` via a 10kΩ Pull-Up.
A4 / SDA	Shared I2C Data Line	In/Out (Digital)	Wired in parallel to LCD `SDA`, LIS3MDL `SDA`, and LSM6DSOX `SDA`.
A5 / SCL	Shared I2C Clock Line	Output (Digital)	Wired in parallel to LCD `SCL`, LIS3MDL `SCL`, and LSM6DSOX `SCL`.
D2	LCD Soft Power Switch	Input (Digital)	Wired to SPST Toggle Switch. Internal Pull-up active (`INPUT_PULLUP`). Toggles D2 to GND.
D3	LCD Backlight Switch	Input (Digital)	Wired to SPST Toggle Switch. Internal Pull-up active (`INPUT_PULLUP`). Toggles D3 to GND.

🛠️ 5. Troubleshooting & Diagnostics

The Arduino sketch features Active I2C Hardware Pings at startup to verify bus integrity without blocking:

Bus Scan: On setup(), the MCU pings addresses 0x27, 0x1E, and 0x6A using non-blocking transmissions.
Graceful Bypass: If a component does not return status 0, its diagnostic flag is set to offline and its query loops are entirely bypassed.
Serial Stream Alerts: The serial output immediately formats connection statuses:
- LCD offline: "lcd":0
- Compass offline: "cps":0 (dashboard uses GPS stream fallback automatically)
- Gyro offline: "gyr":0 (dashboard uses internal phone accelerometer fallback automatically)

📦 1. Bill of Materials (BOM)​

⚙️ 2. Rotary Switch Resistor Ladder Circuit Design​

Resistor Ladder Schematic​

Voltage Divider & 10-bit ADC Mapping Table​

🔌 3. Complete System Wiring Diagram​

📌 4. Microcontroller Pinout Assignment​

🛠️ 5. Troubleshooting & Diagnostics​