From 8aae6d4003a70d7061becdca193ea8e178df4dca Mon Sep 17 00:00:00 2001
From: John Poole <jlpoole56@gmail.com>
Date: Thu, 16 Apr 2026 10:08:15 -0700
Subject: [PATCH] previously meant to include this exercise, too

---
 exercises/22_compass/README.md                | 218 ++++++++++++++++++
 exercises/22_compass/declination_manual.txt   |   1 +
 exercises/22_compass/platformio.ini           | 123 ++++++++++
 .../22_compass/scripts/fetch_declination.pl   | 121 ++++++++++
 .../22_compass/scripts/set_build_epoch.py     |  12 +
 5 files changed, 475 insertions(+)
 create mode 100644 exercises/22_compass/README.md
 create mode 100644 exercises/22_compass/declination_manual.txt
 create mode 100644 exercises/22_compass/platformio.ini
 create mode 100644 exercises/22_compass/scripts/fetch_declination.pl
 create mode 100644 exercises/22_compass/scripts/set_build_epoch.py

diff --git a/exercises/22_compass/README.md b/exercises/22_compass/README.md
new file mode 100644
index 0000000..4ab1bdb
--- /dev/null
+++ b/exercises/22_compass/README.md
@@ -0,0 +1,218 @@
+# Exercise 22: Compass / Magnetometer Executive Summary
+
+This exercise will target the T-Beam Supreme magnetometer and build toward a real-time compass / field monitor. The manufacturer examples reviewed were:
+
+- `QMC6310_CalibrateExample`
+- `QMC6310_CompassExample`
+- `QMC6310_GetDataExample`
+- `QMC6310_GetPolarExample`
+
+## What The Sensor Is Useful For
+
+The QMC6310-class sensor is a 3-axis magnetometer. In practical terms, it is useful for:
+
+- Magnetic heading estimation: a compass that points toward magnetic north.
+- Relative orientation work: detecting yaw changes and turn direction.
+- Magnetic field observation: watching X/Y/Z field components and total field strength change in real time.
+- Sensor fusion: combining magnetometer data with the IMU to stabilize heading over time.
+- Hardware assay: identifying board population differences by probing the magnetometer address and response.
+
+It is not a complete navigation solution by itself. A magnetometer is sensitive to nearby ferrous metal, current-carrying wires, speakers, magnets, and board-level bias. For good heading, it needs calibration and a local magnetic declination correction if the goal is true north rather than magnetic north.
+
+## What Each Example Actually Does
+
+### `QMC6310_GetDataExample`
+
+This is the basic bring-up example. It:
+
+- Uses `setupBoards()` and the board I2C scan to discover the magnetometer address.
+- Initializes the sensor.
+- Configures continuous measurement mode.
+- Prints compensated values and raw values for X/Y/Z to serial.
+
+This is the best starting point for an exercise whose first goal is "show me live data."
+
+### `QMC6310_GetPolarExample`
+
+This example is the smallest heading-oriented demo. It:
+
+- Reads magnetometer data.
+- Converts the reading to a polar heading.
+- Applies a declination correction.
+- Prints heading, Gauss, and microtesla values.
+
+This is useful once raw axis data is already trusted.
+
+### `QMC6310_CompassExample`
+
+This is a user-interface example. It:
+
+- Reads X/Y values.
+- Computes a heading with a hard-coded declination.
+- Draws a compass arrow on the OLED.
+- Also emits debug values on serial.
+
+This demonstrates a real-time visual display, but it is still only as good as the underlying calibration.
+
+### `QMC6310_CalibrateExample`
+
+This example computes hard-iron offsets by watching the min/max raw values while the board is slowly rotated. It then applies:
+
+- `x_offset = (x_max + x_min) / 2`
+- `y_offset = (y_max + y_min) / 2`
+- `z_offset = (z_max + z_min) / 2`
+
+Those offsets are passed to `qmc.setOffset(...)`, after which subsequent readings are shifted by those values.
+
+This is a runtime calibration aid, not a persistent factory calibration workflow.
+
+## Calibration: Does It Need To Happen Every Boot?
+
+Short answer: no, not if you save the offsets somewhere and re-apply them at boot.
+
+Important detail from the local driver:
+
+- `setOffset(...)` only stores offsets in the driver object's RAM.
+- The offsets are not written into nonvolatile sensor storage.
+- `begin(...)` calls `initImpl(...)`, and `initImpl(...)` performs `reset()`.
+
+Implications:
+
+- A normal reboot loses the offsets unless your firmware stores them elsewhere.
+- Removing main power loses them.
+- Keeping a battery attached does not make these software offsets persist in the magnetometer.
+- If the board environment has not changed, you do not need to physically recalibrate at every boot, but you do need to reload previously measured offsets from persistent storage.
+
+Recommended practice for this exercise:
+
+- Add a one-time calibration mode.
+- Save the resulting offsets in persistent storage on the ESP32.
+- Re-apply offsets automatically at startup.
+- Re-run calibration only when the enclosure, mounting, nearby wiring, or magnetic environment changes.
+
+## Declination Offset
+
+Declination is separate from magnetometer calibration.
+
+- Calibration removes local sensor bias and board-level hard-iron offset.
+- Declination converts magnetic north into true north for a specific latitude, longitude, and date.
+
+So yes: if you want true heading, the user should specify a coordinate, obtain the current declination for that coordinate, and store that value with provenance.
+
+For this exercise, the practical design is:
+
+1. Choose the operating coordinates.
+2. Obtain declination on the host, not on the ESP32.
+3. Save the fetched value in a simple text file such as `declination.txt`.
+4. Load that value into firmware at build time or into ESP32 persistent storage at provisioning time.
+5. Re-fetch when the unit is moved a meaningful distance or after enough time has passed that the stored date is stale.
+
+Why host-side instead of device-side:
+
+- The ESP32 firmware should not depend on live network access to a geomagnetic service.
+- Declination changes slowly, so caching is appropriate.
+- A text file with comments gives you traceability for how the value was obtained.
+
+Recommended file shape:
+
+```text
+# procured: April 16, 2026
+# for coordinates: 44.93642012667761, -123.02203699545396
+# source: NOAA/NCEI geomagnetic declination calculator
+# sign convention: east positive, west negative
+declination_deg=14.47
+```
+
+For your current manually captured value:
+
+```text
+2026-04-16      14.47° E  ± 0.36°  changing by 0.11° W per year
+```
+
+the appropriate build-time value is:
+
+```text
+MAG_DECLINATION_DEG = 14.47
+```
+
+using the convention:
+
+- East declination is positive.
+- West declination is negative.
+
+That convention should be written directly into the firmware and README so there is no hidden sign ambiguity.
+
+Operational guidance:
+
+- For a fixed station, one fetched value is usually sufficient and should simply be refreshed occasionally.
+- For a mobile unit used across a region, a single fixed declination is still acceptable for an early exercise, but it should be understood as an approximation.
+- For this project stage, storing one deployment-specific declination value is the right tradeoff.
+
+## Multi-Unit Assay For Seven Boards
+
+Lewis He's current note says T-Beam Supreme units may contain `QMC6310N`, `QMC6310U`, or `QMC6309`, each with a different I2C address.
+
+What the local LilyGo code currently supports:
+
+- `0x1C` -> treated as `QMC6310U`
+- `0x3C` -> treated as `QMC6310N` after distinguishing it from the OLED at the same address family
+
+What is missing locally:
+
+- I do not see `QMC6309` support anywhere in the local clone.
+- The referenced GitHub commit is not present in the local repository, so the current local examples cannot yet identify `QMC6309`.
+
+Practical assay recommendation for units `A` through `G`:
+
+1. Build a small probe sketch for a selected PlatformIO environment such as `cy`.
+2. Run the same board scan that `setupBoards()` already performs.
+3. Print the detected magnetometer I2C address.
+4. Print `getChipID()`.
+5. Record the result per unit label: `AMY`, `BOB`, `CY`, `DAN`, `ED`, `FLO`, `GUY`.
+
+Expected result set:
+
+- If the unit answers at `0x1C`, classify it as `QMC6310U`.
+- If the unit answers at `0x3C`, classify it as `QMC6310N`.
+- If a unit answers at some third address, that is the candidate path for `QMC6309`, but the local code will need to be extended to name it explicitly.
+
+## Recommended Design Direction For This Exercise
+
+The clean design is a real-time serial-first field monitor, with OLED support as a secondary display.
+
+Suggested output in real time:
+
+- Unit identifier, for example `CY`
+- Detected magnetometer address
+- Chip ID
+- Build UTC tag
+- Raw X/Y/Z
+- Offset-corrected X/Y/Z
+- Declination in degrees and its source date
+- Heading in degrees
+- Total field magnitude
+- Calibration status
+
+Suggested workflow:
+
+1. Boot and identify the attached board and detected magnetometer address.
+2. Load saved calibration offsets if present.
+3. Stream readings continuously over serial for capture and inspection.
+4. Optionally mirror heading and a simple arrow on the OLED.
+5. Provide a serial command or compile-time mode to enter calibration.
+6. Save newly computed offsets for future boots.
+7. Apply stored declination before reporting true heading.
+
+## Bottom Line
+
+The examples are enough to establish that this sensor is suitable for a live heading and magnetic field display exercise. The only caution is that the example labeled "calibration" is session-local unless we explicitly persist the offsets. The first useful deliverable for this exercise should therefore be a per-unit magnetometer assay plus a serial real-time monitor, followed by persistent calibration storage and then an OLED compass view.
+
+## Local Helper Scripts
+
+Exercise 22 now includes:
+
+- `scripts/set_build_epoch.py` copied from Exercise 18 so the same unique build timestamp mechanism is available here.
+- `scripts/fetch_declination.pl` to fetch a declination value on the host and write a provenance-rich `declination.txt`.
+- `platformio.ini` scaffolded with the build-stamp hook and manual declination build defines.
+
+The NOAA fetch helper remains available, but given the current registration requirement, the recommended workflow is manual lookup plus a checked-in text record such as `declination_manual.txt`.
diff --git a/exercises/22_compass/declination_manual.txt b/exercises/22_compass/declination_manual.txt
new file mode 100644
index 0000000..3b81b15
--- /dev/null
+++ b/exercises/22_compass/declination_manual.txt
@@ -0,0 +1 @@
+2026-04-16 	14.47° E  ± 0.36°  changing by  0.11° W per year 
diff --git a/exercises/22_compass/platformio.ini b/exercises/22_compass/platformio.ini
new file mode 100644
index 0000000..6dad222
--- /dev/null
+++ b/exercises/22_compass/platformio.ini
@@ -0,0 +1,123 @@
+; 20260416 ChatGPT
+; Exercise 22_compass
+
+[platformio]
+default_envs = cy
+
+[env]
+platform = espressif32
+framework = arduino
+board = esp32-s3-devkitc-1
+board_build.partitions = default_8MB.csv
+monitor_speed = 115200
+extra_scripts = pre:scripts/set_build_epoch.py
+lib_deps =
+  Wire
+  olikraus/U8g2@^2.36.4
+  lewisxhe/XPowersLib@0.3.3
+
+build_flags =
+  -I ../../shared/boards
+  -I ../../external/microReticulum_Firmware
+  -D BOARD_MODEL=BOARD_TBEAM_S_V1
+  -D OLED_SDA=17
+  -D OLED_SCL=18
+  -D OLED_ADDR=0x3C
+  -D GPS_RX_PIN=9
+  -D GPS_TX_PIN=8
+  -D GPS_WAKEUP_PIN=7
+  -D GPS_1PPS_PIN=6
+  -D GPS_L76K
+  -D NODE_SLOT_COUNT=7
+  -D ARDUINO_USB_MODE=1
+  -D ARDUINO_USB_CDC_ON_BOOT=1
+
+  ; Declination convention:
+  ;   east = positive
+  ;   west = negative
+  ; Manual source:
+  ;   declination_manual.txt
+  ;   2026-04-16  14.47° E ±0.36° changing by 0.11° W per year
+  -D MAG_DECLINATION_DEG=14.47f
+  -D MAG_DECLINATION_SOURCE=\"manual_noaa_web_ui\"
+  -D MAG_DECLINATION_DATE=\"2026-04-16\"
+  -D MAG_DECLINATION_LAT=44.93642012667761
+  -D MAG_DECLINATION_LON=-123.02203699545396
+
+[env:amy]
+extends = env
+build_flags =
+  ${env.build_flags}
+  -D BOARD_ID=\"AMY\"
+  -D NODE_LABEL=\"Amy\"
+  -D NODE_SHORT=\"A\"
+  -D NODE_SLOT_INDEX=0
+  -D LOG_AP_IP_OCTET=23
+  -D GNSS_CHIP_NAME=\"L76K\"
+
+[env:bob]
+extends = env
+build_flags =
+  ${env.build_flags}
+  -D BOARD_ID=\"BOB\"
+  -D NODE_LABEL=\"Bob\"
+  -D NODE_SHORT=\"B\"
+  -D NODE_SLOT_INDEX=1
+  -D LOG_AP_IP_OCTET=24
+  -D GNSS_CHIP_NAME=\"L76K\"
+
+[env:cy]
+extends = env
+build_flags =
+  ${env.build_flags}
+  -D BOARD_ID=\"CY\"
+  -D NODE_LABEL=\"Cy\"
+  -D NODE_SHORT=\"C\"
+  -D NODE_SLOT_INDEX=2
+  -D LOG_AP_IP_OCTET=25
+  -D GNSS_CHIP_NAME=\"L76K\"
+
+[env:dan]
+extends = env
+build_flags =
+  ${env.build_flags}
+  -D BOARD_ID=\"DAN\"
+  -D NODE_LABEL=\"Dan\"
+  -D NODE_SHORT=\"D\"
+  -D NODE_SLOT_INDEX=3
+  -D LOG_AP_IP_OCTET=26
+  -D GNSS_CHIP_NAME=\"L76K\"
+
+[env:ed]
+extends = env
+build_flags =
+  ${env.build_flags}
+  -D BOARD_ID=\"ED\"
+  -D NODE_LABEL=\"Ed\"
+  -D NODE_SHORT=\"E\"
+  -D NODE_SLOT_INDEX=4
+  -D LOG_AP_IP_OCTET=27
+  -D GNSS_CHIP_NAME=\"L76K\"
+
+[env:flo]
+extends = env
+build_flags =
+  ${env.build_flags}
+  -D BOARD_ID=\"FLO\"
+  -D NODE_LABEL=\"Flo\"
+  -D NODE_SHORT=\"F\"
+  -D NODE_SLOT_INDEX=5
+  -D LOG_AP_IP_OCTET=28
+  -D GNSS_CHIP_NAME=\"L76K\"
+
+[env:guy]
+extends = env
+build_flags =
+  ${env.build_flags}
+  -D BOARD_ID=\"GUY\"
+  -D NODE_LABEL=\"Guy\"
+  -D NODE_SHORT=\"G\"
+  -D NODE_SLOT_INDEX=6
+  -D LOG_AP_IP_OCTET=29
+  -D GNSS_CHIP_NAME=\"MAX-M10S\"
+  -D GPS_UBLOX
diff --git a/exercises/22_compass/scripts/fetch_declination.pl b/exercises/22_compass/scripts/fetch_declination.pl
new file mode 100644
index 0000000..0893120
--- /dev/null
+++ b/exercises/22_compass/scripts/fetch_declination.pl
@@ -0,0 +1,121 @@
+#!/usr/bin/env perl
+
+use strict;
+use warnings;
+
+use HTTP::Tiny;
+use POSIX qw(strftime);
+use Text::ParseWords qw(parse_line);
+use URI::Escape qw(uri_escape);
+
+my ($lat, $lon, $outfile, $iso_date) = @ARGV;
+
+die usage() unless defined $lat && defined $lon;
+
+$outfile  ||= "declination.txt";
+$iso_date ||= strftime("%Y-%m-%d", gmtime());
+
+die "Latitude must be numeric\n"  unless $lat =~ /\A-?\d+(?:\.\d+)?\z/;
+die "Longitude must be numeric\n" unless $lon =~ /\A-?\d+(?:\.\d+)?\z/;
+die "Latitude out of range\n"     unless $lat >= -90 && $lat <= 90;
+die "Longitude out of range\n"    unless $lon >= -180 && $lon <= 180;
+die "Date must be YYYY-MM-DD\n"   unless $iso_date =~ /\A(\d{4})-(\d{2})-(\d{2})\z/;
+
+my ($year, $month, $day) = ($1, $2, $3);
+
+my $base_url = "https://www.ngdc.noaa.gov/geomag-web/calculators/calculateDeclination";
+my %query = (
+    lat1         => $lat,
+    lon1         => $lon,
+    model        => "WMM",
+    startYear    => $year,
+    startMonth   => $month + 0,
+    startDay     => $day + 0,
+    resultFormat => "csv",
+);
+
+my $url = $base_url . "?" . join("&",
+    map { uri_escape($_) . "=" . uri_escape($query{$_}) } sort keys %query
+);
+
+my $http = HTTP::Tiny->new(
+    agent      => "microReticulum-ex22-declination-fetch/1.0",
+    timeout    => 30,
+    verify_SSL => 1,
+);
+
+my $res = $http->get($url);
+die "HTTP request failed: $res->{status} $res->{reason}\n" unless $res->{success};
+
+my $body = $res->{content};
+my $declination = extract_declination_from_csv($body);
+$declination = extract_declination_from_text($body) unless defined $declination;
+
+die "Unable to parse declination from NOAA response\n" unless defined $declination;
+
+my $procured = format_procured_date($year, $month, $day);
+open my $fh, ">", $outfile or die "Cannot write $outfile: $!\n";
+print {$fh} "# procured: $procured\n";
+print {$fh} "# for coordinates: $lat, $lon\n";
+print {$fh} "# source: NOAA/NCEI geomagnetic declination calculator\n";
+print {$fh} "# date: $iso_date\n";
+print {$fh} "# sign convention: east positive, west negative\n";
+printf {$fh} "declination_deg=%.6f\n", $declination;
+close $fh or die "Cannot close $outfile: $!\n";
+
+print "Wrote $outfile\n";
+printf "declination_deg=%.6f\n", $declination;
+
+sub extract_declination_from_csv {
+    my ($text) = @_;
+    my @lines = grep { /\S/ } split /\r?\n/, $text;
+    return undef unless @lines >= 2;
+
+    my @header = parse_line(",", 0, $lines[0] // "");
+    my $decl_idx;
+    for my $i (0 .. $#header) {
+        next unless defined $header[$i];
+        if ($header[$i] =~ /\Adeclination\z/i) {
+            $decl_idx = $i;
+            last;
+        }
+    }
+    return undef unless defined $decl_idx;
+
+    for my $line (@lines[1 .. $#lines]) {
+        my @fields = parse_line(",", 0, $line);
+        next unless defined $fields[$decl_idx];
+        my $value = $fields[$decl_idx];
+        $value =~ s/^\s+|\s+$//g;
+        $value =~ s/[^\d+.\-]//g;
+        return $value + 0 if $value =~ /\A[+-]?\d+(?:\.\d+)?\z/;
+    }
+
+    return undef;
+}
+
+sub extract_declination_from_text {
+    my ($text) = @_;
+    return $1 + 0 if $text =~ /declination[^-+0-9]*([+-]?\d+(?:\.\d+)?)/i;
+    return undef;
+}
+
+sub format_procured_date {
+    my ($y, $m, $d) = @_;
+    my @month_names = qw(
+        January February March April May June
+        July August September October November December
+    );
+    my $name = $month_names[$m - 1] // die "Invalid month\n";
+    return sprintf("%s %d, %04d", $name, $d, $y);
+}
+
+sub usage {
+    return <<"USAGE";
+Usage:
+  fetch_declination.pl <latitude> <longitude> [outfile] [YYYY-MM-DD]
+
+Example:
+  fetch_declination.pl 44.93642012667761 -123.02203699545396 declination.txt 2026-04-16
+USAGE
+}
diff --git a/exercises/22_compass/scripts/set_build_epoch.py b/exercises/22_compass/scripts/set_build_epoch.py
new file mode 100644
index 0000000..40ef7ca
--- /dev/null
+++ b/exercises/22_compass/scripts/set_build_epoch.py
@@ -0,0 +1,12 @@
+import time
+Import("env")
+
+epoch = int(time.time())
+utc_tag = time.strftime("%Y%m%d_%H%M%S_z", time.gmtime(epoch))
+
+env.Append(
+    CPPDEFINES=[
+        ("FW_BUILD_EPOCH", str(epoch)),
+        ("FW_BUILD_UTC", '"%s"' % utc_tag),
+    ]
+)