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====== The Corvid Compass: A Gaze-Based Sixth Sense ======

This project focuses on a discrete addition to your **glasses** or **hat**, providing a subtle haptic "nudge" toward **Magnetic North** based on where you are gazing.

The "Corvid Compass" is a compact, versatile charm. It can also be tucked **behind the ear**, or even hidden under a **beard**!
  * Though optimised for **headwear,** it can be clipped to a **jacket cuff** or worn as a **pendent** at the cost of head-tracking, your body instead must face North.

Wherever it sits, it gives you that migratory "sixth sense" birds have.

===== Form Factor & Vertical Profile =====

w/ comparisons to AA/AAA batteries, SD card and 2x dollar coins.

^ Configuration ^ Length ^ Width ^ Height (Thickness) ^ Best For... ^
| **The In-Line** | 60mm (AA) | 12mm (AA) | **~4mm** (Two loonies) | Flat glasses frames, hat. |
| **The Sandwich** | 25mm (SD card) | 18mm (AAA) | **~9mm** (AAA) | Tucking behind the ear, on body. |

===== The Shiny Bits (BOM) =====

^ Item ^ Part Number ^ Description ^ Unit Cost (CAD) ^ Note ^
| **The Brain** | PIC16F18313-I/SN | 8-pin SOIC Microcontroller | $1.36 | Low power, high IQ. |
| **The Sense** | Adafruit 4413 | LSM303AGR Breakout Board | $18.08 | **Or bare chip: ~$6.50** |
| **The Muscle** | 2N7002 | N-Channel MOSFET (SOT-23) | $0.52 | To switch the motor. |
| **The Pulse** | Seeed 316040004 | 10mm Vibration ERM Motor | $1.85 | Tiny haptic feedback. |
| **The Power** | MPD BK-885 | 12mm Coin Cell Retainer | $0.84 | For a CR1220 battery. |

**Total Est. Cost per Unit: ~$11.07 - $22.98 CAD.**

[[https://www.digikey.ca/short/wr7p9npv|Digikey.ca Shopping Cart]] - [[https://www.digikey.com/short/wr7p9npv|[.com/USD]]]

===== Alternatives =====

Perhaps you desire shiny alternatives, or even better sensors you may reuse:

==== High-Altitude Options (Absolute Orientation) ====
If you want the chip to do all the heavy math (Tilt-compensation, Calibration) for you:
  * **The "Auto-Pilot" (BNO055):** ~**$45.00 CAD**. An Intelligent 9-DOF sensor. Outputs a stable "North" vector directly. No complex math required!

==== Scavenger Options (Budget) ====
If the Adafruit board is out of stock or you wish to save some shiny coins:
  * **The "Budget Bird" (QMC5883L):** ~**$4.50 CAD**. No accelerometer. Works only if held perfectly level.
  * **The "Middle Magpie" (Bare LSM303AGR):** ~**$6.50 CAD**. Buy just the chip and solder it to an LGA-12 adapter. Cheaper, but requires a steady talon and a hot air station.
  * **The "Pro Crow" (Harvested):** **$0.00 CAD**. Harvest a sensor of an old cellphone/electronic containing a compass. Common targets include:
    * **Bosch BMC150** (LGA-14, found in PS4 DualShock 4)
    * **MPU-9250** (QFN-24, found in toy drones)
    * **LSM303DLHC** (LGA-14, found in Samsung S3/S4 or Note 2)

===== The Map (Schematic) =====

This is the logical map of the nest. Keep your connections short to avoid noise.

<code>
3.0V >---------+------------------+--------------( MOTOR )
               |                  |                  |
            [ VIN ]               |             +----------+
         +-----------+            |             |  DRAIN   |
         |  LSM303   |            |             +----------+
         |  SENSOR   |            |             |  2N7002  |
         +-----------+            +-------------|  GATE    |
         [SCL]   [SDA]            |             +----------+
           |       |              |             |  SOURCE  |
           |       |              |             +----------+
           |       |       [ VDD / PIN 1 ]           |
           |       |      +----------------+         |
           +-------|------| SCL / PIN 6    |         |
                   +------| SDA / PIN 5    |         |
                          | PWM / PIN 2    |---------+
                          +----------------+
                            [ VSS / PIN 8 ]
                                  |
 GND >----------------------------+------------------+
</code>

===== Bird Logic: The Firmware (C Code) =====

This code reads the compass and decides when to buzz. It includes basic **Tilt Compensation** so looking down doesn't confuse it. **+/-10 deg** is considered North.

<code c>
#include <xc.h>
#include <math.h>

// PIC16F18313 Configuration
#define MOTOR_PIN LATA2   // Pin 2
#define PWM_PERIOD 0xFF   // Max PWM period

void main(void) {
    // Setup PWM on RA2 (Pin 2) for motor control
    TRISA2 = 0;           // Make Pin 2 Output
    CCP1CON = 0x8F;       // PWM Mode
    PR2 = PWM_PERIOD;     // Set Frequency
    T2CON = 0x04;         // Timer2 On

    float heading;
    int intensity = 0;

    while(1) {
        // 1. Read I2C Data (LSM303)
        // [Insert I2C Read Function Here]

        // 2. Calculate Heading (Simplified)
        // (Full tilt-compensation math omitted for brevity)
        heading = atan2(my, mx) * (180.0 / M_PI);
        if (heading < 0) heading += 360;

        // 3. LOGIC: Is it North? (Window: 350 to 10 degrees)
        if (heading > 350 || heading < 10) {
            CCPR1L = 255; // Full Power Buzz!
        } else {
            CCPR1L = 0;   // Silence
        }
    }
}
</code>

==== Variant: The "Analog Sense" (Variable Intensity) ====

If you want to feel *how close* you are to North (faint buzz at West/East, strong buzz at North), replace **Step 3** in the code above with this block:

<code c>
// 3. VARIANT LOGIC: Variable Intensity
// Calculate error from North (0 degrees)
float error = heading;
if (error > 180) error = 360 - error; // Normalize to 0-180 range

// If within +/- 90 degrees of North...
if (error < 90) {
    // Map intensity: 0 error = Max Speed, 90 error = Min Speed
    // This creates a "magnetic pull" feeling
    intensity = (int)(255 * (1.0 - (error / 90.0)));
    CCPR1L = intensity; 
} else {
    CCPR1L = 0; // Total silence behind you (South)
}
</code>

===== KiCad Source =====

[[https://www.kicad.org/|KiCad]] is my choice for Open Source Electronic Design CAD.

Save this text as ''bird_sense.kicad_sch'' to open the schematic in KiCad.

Note: **WIP** draft - non-functional currently.
<code lisp>
(kicad_sch (version 20260101) (generator eeschema)
  (uuid 89db6782-0164-4682-9531-15822f6d81be)
  (paper "A4")
  (lib_symbols
    (symbol "MCU_Microchip_PIC16:PIC16F18313-ISN" (in_bom yes) (on_board yes))
    (symbol "Sensor_Magnetic:LSM303AGR" (in_bom yes) (on_board yes))
    (symbol "Transistor_FET:2N7002" (in_bom yes) (on_board yes))
  )
  (wire (pts (xy 127.0 101.6) (xy 139.7 101.6)) (uuid w1))
  (text "Corvid Compass v1.0" (at 150 20) (effects (font (size 1.5 1.5))))
)
</code>

===== Closing Thoughts =====

Building your own senses is the ultimate way to explore your territory. Just remember: measure twice, solder once -- and keep your bits shiny with flux!

Caw for now!
nest

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