diff --git a/.github/scripts/check_shared_blocks.py b/.github/scripts/check_shared_blocks.py
new file mode 100644
index 0000000..086b41d
--- /dev/null
+++ b/.github/scripts/check_shared_blocks.py
@@ -0,0 +1,96 @@
+#!/usr/bin/env python3
+"""Shared code check: the blocks the sprayer and the seed drill modules have in common must stay the same.
+
+Sprayer/Sprayer_ESP32 and Seeder/Seeder_ESP32 are two programs with one origin: the Wi-Fi, the web helpers, the
+settings for the network, the PGN handling and the relay driving are the same code in both. Those parts are
+marked in the sources, with the same name in both programs:
+
+    // ==== shared "web-helpers": ...
+    ... the code ...
+    // ==== end shared "web-helpers"
+
+This script reads every .ino of both programs, pairs the blocks by name and fails when a block differs, is
+missing from one program, is nested, or is not closed. Run it from the repository root: no arguments, no
+packages, exit code 1 when something is wrong. The "Shared code" GitHub Action runs it on every pull request
+that touches either program.
+
+Licence: GNU General Public License v3 or later (Firmware/v4.5_AiO_WEB/COPYING).
+SPDX-License-Identifier: GPL-3.0-or-later
+"""
+import difflib
+import glob
+import os
+import re
+import sys
+
+ROOT = os.path.dirname(os.path.dirname(os.path.dirname(os.path.abspath(__file__))))
+PROGRAMS = {"Sprayer_ESP32": "Sprayer/Sprayer_ESP32", "Seeder_ESP32": "Seeder/Seeder_ESP32"}
+START = re.compile(r'^\s*// ==== shared "([^"]+)"')
+END = re.compile(r'^\s*// ==== end shared "([^"]+)"\s*$')
+
+
+def read_blocks(folder, errors):
+    """{name: (file, first line number, lines)} of one program; problems go to errors"""
+    found = {}
+    for path in sorted(glob.glob(os.path.join(ROOT, folder, "*.ino"))):
+        rel = os.path.relpath(path, ROOT)
+        with open(path, encoding="utf-8") as f:
+            lines = f.read().split("\n")
+        open_name, open_at, body = None, 0, []
+        for n, line in enumerate(lines, 1):
+            m = START.match(line)
+            if m:
+                if open_name:
+                    errors.append(f'{rel}:{n}: shared "{m.group(1)}" starts inside "{open_name}" (opened at line {open_at})')
+                    continue
+                open_name, open_at, body = m.group(1), n, []
+                continue
+            m = END.match(line)
+            if m:
+                if not open_name:
+                    errors.append(f'{rel}:{n}: end of shared "{m.group(1)}" without a start')
+                elif m.group(1) != open_name:
+                    errors.append(f'{rel}:{n}: end of shared "{m.group(1)}" closes "{open_name}" (opened at line {open_at})')
+                else:
+                    if open_name in found:
+                        errors.append(f'{rel}:{open_at}: shared "{open_name}" is already in {found[open_name][0]}:{found[open_name][1]}')
+                    else:
+                        found[open_name] = (rel, open_at + 1, body)
+                    open_name = None
+                continue
+            if open_name:
+                body.append(line.rstrip())
+        if open_name:
+            errors.append(f'{rel}:{open_at}: shared "{open_name}" is never closed')
+    return found
+
+
+def main():
+    errors = []
+    blocks = {name: read_blocks(folder, errors) for name, folder in PROGRAMS.items()}
+    (a, blocks_a), (b, blocks_b) = blocks.items()
+    for name in sorted(set(blocks_a) ^ set(blocks_b)):
+        where = blocks_a.get(name) or blocks_b.get(name)
+        other = b if name in blocks_a else a
+        errors.append(f'{where[0]}:{where[1]}: shared "{name}" has no block of that name in {other}')
+    same_lines = 0
+    for name in sorted(set(blocks_a) & set(blocks_b)):
+        fa, la, ba = blocks_a[name]
+        fb, lb, bb = blocks_b[name]
+        if ba == bb:
+            same_lines += len(ba)
+            continue
+        diff = difflib.unified_diff(ba, bb, fromfile=f"{fa}:{la}", tofile=f"{fb}:{lb}", lineterm="", n=1)
+        errors.append(f'shared "{name}" differs between {a} and {b}: change both the same way, or move the line out of the block\n' + "\n".join(diff))
+    for e in errors:
+        print(e)
+    if errors:
+        print(f"{len(errors)} problem(s) in the shared blocks")
+        return 1
+    n = len(set(blocks_a) & set(blocks_b))
+    print(f"OK: {n} shared blocks, {same_lines} lines the same in {a} and {b}")
+    return 0
+
+
+if __name__ == "__main__":
+    sys.exit(main())
diff --git a/.github/workflows/shared-code.yml b/.github/workflows/shared-code.yml
new file mode 100644
index 0000000..f661cdd
--- /dev/null
+++ b/.github/workflows/shared-code.yml
@@ -0,0 +1,38 @@
+# Shared code check.
+# The sprayer and the seed drill modules (Sprayer/Sprayer_ESP32, Seeder/Seeder_ESP32) have the same code in the
+# blocks marked `// ==== shared "name"` ... `// ==== end shared "name"`. A change to one that is not made to the
+# other fails this check, so the pull request shows it before it is merged. .github/scripts/check_shared_blocks.py
+# does the work (plain Python 3, no packages). It runs only when either program, the script or this file changes.
+# Licence: GNU General Public License v3 or later (Firmware/v4.5_AiO_WEB/COPYING).
+# SPDX-License-Identifier: GPL-3.0-or-later
+
+name: Shared code
+
+on:
+  pull_request:
+    paths:
+      - 'Sprayer/Sprayer_ESP32/**'
+      - 'Seeder/Seeder_ESP32/**'
+      - '.github/scripts/check_shared_blocks.py'
+      - '.github/workflows/shared-code.yml'
+  push:
+    branches: [main]
+    paths:
+      - 'Sprayer/Sprayer_ESP32/**'
+      - 'Seeder/Seeder_ESP32/**'
+      - '.github/scripts/check_shared_blocks.py'
+      - '.github/workflows/shared-code.yml'
+
+permissions:
+  contents: read
+
+jobs:
+  blocks:
+    name: blocks
+    runs-on: ubuntu-latest
+    timeout-minutes: 5
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Compare the shared blocks of the sprayer and the seed drill programs
+        run: python3 .github/scripts/check_shared_blocks.py
diff --git a/CLAUDE.md b/CLAUDE.md
index f3e548d..5019604 100644
--- a/CLAUDE.md
+++ b/CLAUDE.md
@@ -32,6 +32,10 @@ text to paste into GitHub as a raw markdown code block.
   page find new versions on GitHub by those names (see the firmware `CLAUDE.md`, "Common Gotchas").
 - The firmware steers a tractor: safety code (WAS check, cut-offs, Keya heartbeat, watchdog) must keep working.
 - Pull requests: one topic each, a short plain description of what changes for Renato and how to test it.
+- `Sprayer/Sprayer_ESP32` and `Seeder/Seeder_ESP32` have the same code in the blocks marked `// ==== shared "name"` …
+  `// ==== end shared "name"` (Wi-Fi, web helpers, network settings, PGN handling, relays). Change both the same way,
+  or move a line out of the block: `.github/scripts/check_shared_blocks.py` compares them on every pull request
+  (the "Shared code" check). What is only one module's (sensors, rate, the cable, the relays setting) stays outside.
 - README changelogs: one short row per day (a summary of up to 240 characters, with links to the sections that
   hold the details). `.github/scripts/check_changelog.py` checks them on every pull request (the "Docs" check).
 
diff --git a/Firmware/simulator/sim-sprayer.js b/Firmware/simulator/sim-sprayer.js
index a3d3bc4..46071c2 100644
--- a/Firmware/simulator/sim-sprayer.js
+++ b/Firmware/simulator/sim-sprayer.js
@@ -164,7 +164,7 @@ function wifiPost(b) {
  if (b.staPass || staSsid !== X.sta) X.staPassSet = !!b.staPass;   // a new network without a password: an open one
  Object.assign(X, {ap: b.apSsid, staOn: staOn, sta: staSsid, host: b.host, subnet: net, ipLast: b.ipLast === undefined ? X.ipLast : +b.ipLast});
  if (b.apPass) X.pass = b.apPass;
- event("Wi-Fi settings saved from the page, restarting");
+ event("network settings saved from the page, restarting");
  restart(3000);
  return S.ok({ok: true, restart: true});
 }
diff --git a/Seeder/Seeder_ESP32/README.md b/Seeder/Seeder_ESP32/README.md
index 0254d2f..64c004d 100644
--- a/Seeder/Seeder_ESP32/README.md
+++ b/Seeder/Seeder_ESP32/README.md
@@ -20,7 +20,7 @@ One row per day, in short; the details are in the sections of this file (the lin
 
 | Date | What changed |
 |---|---|
-| 7 Nov 2026 | **0.2.2**: add-on card (`_aowcard._tcp`) under its Wi-Fi name; `_aow-ui` and `/aow/status` gone ([Notes](#notes)). **0.2.3**: four tabs as the sprayer page's, with Firmware ([How it works](#how-it-works)). **0.2.4**: Module tab: a Module card, one Network settings card. |
+| 7 Nov 2026 | **0.2.2**: add-on card (`_aowcard._tcp`) under its Wi-Fi name; `_aow-ui` and `/aow/status` gone. **0.2.3**: four tabs as the sprayer's ([How it works](#how-it-works)). **0.2.4**: Module tab: Module card, one Network settings card. Code shared with the sprayer marked ([Notes](#notes)). |
 | 2 Nov 2026 | **0.2.1**: the Wi-Fi settings on the page as on the XIAO page, with a search for networks ([Setup](#setup)). |
 | 28 Oct 2026 | **0.2**: runs on the [Relay24_ESP32](#hardware-relay24_esp32) board of this repository, now the default; the [KC868-A32](#hardware-kc868-a32) stays as a choice. |
 | 27 Oct 2026 | **0.1**: the seed drill part of Sprayer_ESP32 0.8 in its own folder: KC868-A32, 19 sections, no sensors, no PGN 160. **0.1.1**: PGN 237 in the AiO v26 layout, the sections above 16 after it, so the [AiO module page](#what-the-aio-module-page-shows) shows them all. |
@@ -270,5 +270,10 @@ messages with a right checksum from source `0x7F` (the program).
   announcement (`Docs/ADD_ON_CARDS.md`), both under the module's own Wi-Fi name
   (`Seeder-xxxx`, "Name on the network" on the page), unique to each module. The earlier
   `_aow-ui._tcp` and `GET /aow/status` (0.1 to 0.2.1) are gone.
+- This program grew out of the sprayer module (`Sprayer/Sprayer_ESP32`): the Wi-Fi, the web helpers, the
+  network settings, the PGN handling and the relay driving are the same code in both, marked in the sources
+  as `// ==== shared "name"` … `// ==== end shared "name"`. A change to one of those blocks goes in both
+  programs: the "Shared code" check (`.github/scripts/check_shared_blocks.py`) compares them on every pull
+  request. The network cable, the sections above 16 and the relays setting are this program's own.
 - Licence: GNU General Public License v3 or later (`Firmware/v4.5_AiO_WEB/COPYING`).
   Written 2026 by Claude (Anthropic) for renatorgr.
diff --git a/Seeder/Seeder_ESP32/Seeder_ESP32.ino b/Seeder/Seeder_ESP32/Seeder_ESP32.ino
index ca3cec8..4452d2f 100644
--- a/Seeder/Seeder_ESP32/Seeder_ESP32.ino
+++ b/Seeder/Seeder_ESP32/Seeder_ESP32.ino
@@ -172,6 +172,7 @@ bool     isRaise = false, isLower = false;
 uint32_t last239Ms = 0, last229Ms = 0, lastHelloMs = 0;
 bool     have239 = false, have229 = false, haveHello = false;
 bool     linkOk = false;        // a PGN 239 or 229 arrived in the last NO_DATA_TIMEOUT_MS
+bool     masterOn = true;       // the seed drill has no master switch (the sprayer's follows its switch): always on
 uint32_t count239 = 0, count229 = 0, countHello = 0, countCrcErr = 0, countOther = 0;
 
 bool     staWasUp = false, ethWasUp = false;
@@ -203,6 +204,7 @@ String defaultApSsid();
 String moduleName();
 
 // ---------------------------------------------------------------- small helpers
+// ==== shared "pgn-checksum": the same in Sprayer_ESP32 and Seeder_ESP32 (change both; check_shared_blocks.py compares them)
 // AgOpenGPS checksum: sum of the bytes from the 3rd up to the one before the checksum
 uint8_t pgnChecksum(const uint8_t* msg, size_t length)
 {
@@ -212,8 +214,10 @@ uint8_t pgnChecksum(const uint8_t* msg, size_t length)
 }
 
 bool staUp() { return cfg.staOn && WiFi.status() == WL_CONNECTED; }
+// ==== end shared "pgn-checksum"
 bool netUp() { return staUp() || ethUp(); }       // on the tractor network, over the cable or Wi-Fi
 
+// ==== shared "log-event": the same in Sprayer_ESP32 and Seeder_ESP32 (change both; check_shared_blocks.py compares them)
 void logEvent(const char* fmt, ...)
 {
     char* b = eventLog[eventNext];
@@ -226,6 +230,7 @@ void logEvent(const char* fmt, ...)
     Serial.println(b);
     eventNext = (eventNext + 1) % 12;
 }
+// ==== end shared "log-event"
 
 static void printStatus()
 {
diff --git a/Seeder/Seeder_ESP32/zNet.ino b/Seeder/Seeder_ESP32/zNet.ino
index 82136d5..b11fb59 100644
--- a/Seeder/Seeder_ESP32/zNet.ino
+++ b/Seeder/Seeder_ESP32/zNet.ino
@@ -102,6 +102,7 @@ void wifiWatch()
     else if (cfg.staOn) logEvent("lost the tractor network '%s'", cfg.staSsid.c_str());
 }
 
+// ==== shared "web-helpers": the same in Sprayer_ESP32 and Seeder_ESP32 (change both; check_shared_blocks.py compares them)
 // ---------------------------------------------------------------- web helpers
 static void sendJson(const String& body, int code = 200)
 {
@@ -142,7 +143,9 @@ static String jsonHex(uint64_t v)
     else snprintf(b, sizeof(b), "\"%lx\"", (unsigned long)v);
     return String(b);
 }
+// ==== end shared "web-helpers"
 
+// ==== shared "request-helpers": the same in Sprayer_ESP32 and Seeder_ESP32 (change both; check_shared_blocks.py compares them)
 // A whole number lo..hi in the request (only digits), else false
 static bool argNumber(const char* name, long lo, long hi, long& out)
 {
@@ -171,6 +174,7 @@ static bool captiveRedirect()
     server.send(302, "text/plain", "");
     return true;
 }
+// ==== end shared "request-helpers"
 
 // ---------------------------------------------------------------- web answers
 static void apiStatus()
@@ -210,6 +214,7 @@ static void apiStatus()
     for (uint8_t i = 0; i < NUM_RELAYS; i++) { if (i) j += ","; j += String(relayFn(i)); }
     j += "]}";
 
+    // ==== shared "status-log": the same in Sprayer_ESP32 and Seeder_ESP32 (change both; check_shared_blocks.py compares them)
     j += ",\"log\":[";
     bool first = true;
     for (uint8_t k = 0; k < 12; k++)
@@ -222,6 +227,7 @@ static void apiStatus()
     }
     j += "]}";
     sendJson(j);
+    // ==== end shared "status-log"
 }
 
 static void apiSettingsGet()
@@ -233,6 +239,7 @@ static void apiSettingsGet()
     sendJson(j);
 }
 
+// ==== shared "network-settings-post": the same in Sprayer_ESP32 and Seeder_ESP32 (change both; check_shared_blocks.py compares them)
 // "192.168.1" -> the three numbers; false when it is not three numbers 0-255
 static bool parseSubnet(const String& text, uint8_t out[3])
 {
@@ -310,6 +317,7 @@ static void apiScan()
     scanState = -1;
     sendJson("{\"busy\":true}");
 }
+// ==== end shared "network-settings-post"
 
 // Relay 1 follows section "first", the next relays the next sections (0 = the program's pin config)
 static void apiRelaysPost()
@@ -325,6 +333,7 @@ static void apiRelaysPost()
     sendJson("{\"ok\":true}");
 }
 
+// ==== shared "restart-update": the same in Sprayer_ESP32 and Seeder_ESP32 (change both; check_shared_blocks.py compares them)
 static void apiRestartPost()
 {
     if (!passwordOk()) return;
@@ -369,6 +378,7 @@ static void notFound()
     if (captiveRedirect()) return;
     server.send(404, "text/plain", "not found");
 }
+// ==== end shared "restart-update"
 
 void webStart()
 {
diff --git a/Seeder/Seeder_ESP32/zOutputs.ino b/Seeder/Seeder_ESP32/zOutputs.ino
index cdb0312..3611cd2 100644
--- a/Seeder/Seeder_ESP32/zOutputs.ino
+++ b/Seeder/Seeder_ESP32/zOutputs.ino
@@ -18,6 +18,7 @@
 // Relay24_ESP32, on a LOW PCF8574 pin on the KC868-A32.
 // cfg.invertOutputs (PGN 238, byte 8 bit 0; the official module calls it isRelayActiveHigh) turns that
 // round: 0 = as built, 1 = inverted.
+// ==== shared "relay-level": the same in Sprayer_ESP32 and Seeder_ESP32 (change both; check_shared_blocks.py compares them)
 // The program sends this setting at start-up and when the machine profile is loaded, so the
 // "relay active high" box in its machine settings normally stays unticked.
 
@@ -27,6 +28,7 @@ static int relayLevel(bool on)
     const bool drive = on != (cfg.invertOutputs != 0);
     return (drive == (RELAY_ON_HIGH != 0)) ? HIGH : LOW;
 }
+// ==== end shared "relay-level"
 
 static uint8_t raiseTimer = 0, lowerTimer = 0, lastTrigger = 0;
 
@@ -112,6 +114,7 @@ void outputsInit()
 }
 #endif
 
+// ==== shared "outputs": the same in Sprayer_ESP32 and Seeder_ESP32 (change both; check_shared_blocks.py compares them)
 // Everything off, whatever the polarity setting says (used before a restart or a program update)
 void outputsAllOff()
 {
@@ -160,7 +163,7 @@ void applyOutputs()
         if (top > secTop) secTop = top;
     }
 
-    const uint64_t req = linkOk ? sectionsReq : 0;
+    const uint64_t req = (linkOk && masterOn) ? sectionsReq : 0;
     const bool other[6] = { false,                          // other[f - FN_OTHER]
                             linkOk && isLower, linkOk && isRaise,
                             linkOk && (tramline & 1), linkOk && (tramline & 2),
@@ -180,4 +183,5 @@ void applyOutputs()
     relaysWrite(bits);
     relayBits = bits;
     sectionsOn = open;
+// ==== end shared "outputs"
 }
diff --git a/Seeder/Seeder_ESP32/zPgn.ino b/Seeder/Seeder_ESP32/zPgn.ino
index d647548..af2e5e0 100644
--- a/Seeder/Seeder_ESP32/zPgn.ino
+++ b/Seeder/Seeder_ESP32/zPgn.ino
@@ -57,6 +57,7 @@ void sendSignOfLife()
     sendPgn(msg, sizeof(msg), broadcastIp());
 }
 
+// ==== shared "pgn-common-cases": the same in Sprayer_ESP32 and Seeder_ESP32 (change both; check_shared_blocks.py compares them)
 static void handlePgn(uint8_t pgn, const uint8_t* d, uint8_t dataLength, IPAddress from)
 {
     switch (pgn)
@@ -113,6 +114,7 @@ static void handlePgn(uint8_t pgn, const uint8_t* d, uint8_t dataLength, IPAddre
         logEvent("machine config from the program: lift %s, raise %u s, lower %u s, outputs %s",
                  cfg.hydEnable ? "on" : "off", cfg.raiseTime, cfg.lowerTime, cfg.invertOutputs ? "INVERTED (relay active high ticked)" : "normal");
         break;
+// ==== end shared "pgn-common-cases"
 
     case 236:                                               // output functions, 24 entries
         if (dataLength < 24) return;
@@ -123,6 +125,7 @@ static void handlePgn(uint8_t pgn, const uint8_t* d, uint8_t dataLength, IPAddre
                  cfg.firstSection ? " (not used: the relays follow the sections in a row)" : "");
         break;
 
+    // ==== shared "pgn-subnet-receive": the same in Sprayer_ESP32 and Seeder_ESP32 (change both; check_shared_blocks.py compares them)
     case 201:                                               // subnet: save and restart with the new IP
         if (dataLength == 5 && d[5] == 201 && d[6] == 201)
         {
@@ -164,3 +167,4 @@ void udpPoll()
         handlePgn(pgn, rx, dataLength, udp.remoteIP());
     }
 }
+    // ==== end shared "pgn-subnet-receive"
diff --git a/Seeder/Seeder_ESP32/zSettings.ino b/Seeder/Seeder_ESP32/zSettings.ino
index 24cc8cf..bc449f7 100644
--- a/Seeder/Seeder_ESP32/zSettings.ino
+++ b/Seeder/Seeder_ESP32/zSettings.ino
@@ -26,6 +26,7 @@ void settingsLoad()
 {
     Settings d;                                             // the defaults
     prefs.begin("seeder", true);
+    // ==== shared "settings-wifi-load": the same in Sprayer_ESP32 and Seeder_ESP32 (change both; check_shared_blocks.py compares them)
     cfg.apSsid  = prefs.getString("apSsid", defaultApSsid());
     cfg.apPass  = prefs.getString("apPass", DEFAULT_AP_PASS);
     cfg.staOn   = prefs.getBool("staOn", false);
@@ -34,6 +35,7 @@ void settingsLoad()
     cfg.host    = prefs.getString("host", DEFAULT_HOST);
     if (prefs.getBytesLength("subnet") == 3) prefs.getBytes("subnet", cfg.subnet, 3);
     cfg.ipLast       = prefs.getUChar("ipLast", d.ipLast);
+    // ==== end shared "settings-wifi-load"
     cfg.firstSection = prefs.getUChar("first", d.firstSection);
     cfg.raiseTime     = prefs.getUChar("raise", d.raiseTime);
     cfg.lowerTime     = prefs.getUChar("lower", d.lowerTime);
@@ -58,6 +60,7 @@ void settingsLoad()
 void settingsSave()
 {
     prefs.begin("seeder", false);
+    // ==== shared "settings-wifi-save": the same in Sprayer_ESP32 and Seeder_ESP32 (change both; check_shared_blocks.py compares them)
     prefs.putString("apSsid", cfg.apSsid);
     prefs.putString("apPass", cfg.apPass);
     prefs.putBool("staOn", cfg.staOn);
@@ -66,6 +69,7 @@ void settingsSave()
     prefs.putString("host", cfg.host);
     prefs.putBytes("subnet", cfg.subnet, 3);
     prefs.putUChar("ipLast", cfg.ipLast);
+    // ==== end shared "settings-wifi-save"
     prefs.putUChar("first", cfg.firstSection);
     prefs.putUChar("raise", cfg.raiseTime);
     prefs.putUChar("lower", cfg.lowerTime);
@@ -81,6 +85,7 @@ void settingsSave()
 
 // Only the Wi-Fi settings and the host name go back to the defaults (a forgotten password); the
 // program's config, the output functions, the module IP and the relays setting stay
+// ==== shared "settings-reset-wifi": the same in Sprayer_ESP32 and Seeder_ESP32 (change both; check_shared_blocks.py compares them)
 void settingsResetWifi()
 {
     cfg.apSsid  = defaultApSsid();
@@ -91,3 +96,4 @@ void settingsResetWifi()
     cfg.host    = DEFAULT_HOST;
     settingsSave();
 }
+// ==== end shared "settings-reset-wifi"
diff --git a/Sprayer/Sprayer_ESP32/README.md b/Sprayer/Sprayer_ESP32/README.md
index 6e5f542..cbb0a7a 100644
--- a/Sprayer/Sprayer_ESP32/README.md
+++ b/Sprayer/Sprayer_ESP32/README.md
@@ -13,7 +13,7 @@ One row per day, in short; the details are in the sections of this file (the lin
 
 | Date | What changed |
 |---|---|
-| 7 Nov 2026 | **0.10.2**: add-on card (`_aowcard._tcp`) under its Wi-Fi name; `_aow-ui` and `/aow/status` gone ([Notes](#notes)). **0.10.3**: alarms also as PGN 221, on the program's screen ([Messages](#messages)). **0.10.4**: Module tab: a Module card, one Network settings card. |
+| 7 Nov 2026 | **0.10.2**: add-on card (`_aowcard._tcp`) under its Wi-Fi name; `_aow-ui` and `/aow/status` gone. **0.10.3**: alarms also as PGN 221 ([Messages](#messages)). **0.10.4**: Module tab: Module card, one Network settings card. Code shared with the seed drill marked ([Notes](#notes)). |
 | 2 Nov 2026 | **0.10**: rate (L/ha), target pressure and alarms worked out on the module and sent to the program (PGN 161); the page gets Spraying, [Settings](#setup), Module and Firmware tabs, with Install from GitHub. **0.10.1**: Wi-Fi settings as on the XIAO page. |
 | 27 Oct 2026 | **0.7.1** sensor dividers from a common resistor kit. **0.7.2** the page says which sensors there are. **0.8** up to 64 sections, relays from any section. **0.9** sprayer boards only (the seed drill got its own folder). **0.9.1** PGN 237 in the AiO v26 layout. |
 | 26 Oct 2026 | **0.6**: all 8 relays are sections by default. **0.7**: also a plain ESP32 with [relay modules](#a-separate-esp32-with-relay-modules), up to 16 relays. The relay number above its function on the page. |
@@ -306,6 +306,11 @@ level the module is using.
   it to the right one or to −1.
 - The FPD-270A valves and the YF-S201 are plastic and made for water. Rinse with clean
   water after each job. Fit a filter before the flow meter.
+- The seed drill module (`Seeder/Seeder_ESP32`) grew out of this program: the Wi-Fi, the web helpers, the
+  network settings, the PGN handling and the relay driving are the same code in both, marked in the sources
+  as `// ==== shared "name"` … `// ==== end shared "name"`. A change to one of those blocks goes in both
+  programs: the "Shared code" check (`.github/scripts/check_shared_blocks.py`) compares them on every pull
+  request. The sensors, the rate and the alarms are this program's own.
 - The ISOBUS group of AgOpenGPS is working on a standard way for modules to send such
   readings (ISOBUS DDIs). PGN 161 follows that proposal; the PGN number itself is this
   project's choice until the group picks one. The module keeps sending PGN 160 for the AiO
diff --git a/Sprayer/Sprayer_ESP32/Sprayer_ESP32.ino b/Sprayer/Sprayer_ESP32/Sprayer_ESP32.ino
index 20135ab..52380b7 100644
--- a/Sprayer/Sprayer_ESP32/Sprayer_ESP32.ino
+++ b/Sprayer/Sprayer_ESP32/Sprayer_ESP32.ino
@@ -229,6 +229,7 @@ String defaultApSsid();
 String moduleName();
 
 // ---------------------------------------------------------------- small helpers
+// ==== shared "pgn-checksum": the same in Sprayer_ESP32 and Seeder_ESP32 (change both; check_shared_blocks.py compares them)
 // AgOpenGPS checksum: sum of the bytes from the 3rd up to the one before the checksum
 uint8_t pgnChecksum(const uint8_t* msg, size_t length)
 {
@@ -238,7 +239,9 @@ uint8_t pgnChecksum(const uint8_t* msg, size_t length)
 }
 
 bool staUp() { return cfg.staOn && WiFi.status() == WL_CONNECTED; }
+// ==== end shared "pgn-checksum"
 
+// ==== shared "log-event": the same in Sprayer_ESP32 and Seeder_ESP32 (change both; check_shared_blocks.py compares them)
 void logEvent(const char* fmt, ...)
 {
     char* b = eventLog[eventNext];
@@ -251,6 +254,7 @@ void logEvent(const char* fmt, ...)
     Serial.println(b);
     eventNext = (eventNext + 1) % 12;
 }
+// ==== end shared "log-event"
 
 static void ledSet(bool on)
 {
diff --git a/Sprayer/Sprayer_ESP32/zNet.ino b/Sprayer/Sprayer_ESP32/zNet.ino
index 5227b1f..81c096e 100644
--- a/Sprayer/Sprayer_ESP32/zNet.ino
+++ b/Sprayer/Sprayer_ESP32/zNet.ino
@@ -62,6 +62,7 @@ void wifiWatch()
     else if (cfg.staOn) logEvent("lost the tractor network '%s'", cfg.staSsid.c_str());
 }
 
+// ==== shared "web-helpers": the same in Sprayer_ESP32 and Seeder_ESP32 (change both; check_shared_blocks.py compares them)
 // ---------------------------------------------------------------- web helpers
 static void sendJson(const String& body, int code = 200)
 {
@@ -102,6 +103,7 @@ static String jsonHex(uint64_t v)
     else snprintf(b, sizeof(b), "\"%lx\"", (unsigned long)v);
     return String(b);
 }
+// ==== end shared "web-helpers"
 
 // A number for the JSON with d decimals; -1 for "none" (a NaN would break the JSON)
 static String jsonNum(float v, uint8_t d)
@@ -124,6 +126,7 @@ static bool argFloat(const char* name, float lo, float hi, float& out)
     return out >= lo && out <= hi;
 }
 
+// ==== shared "request-helpers": the same in Sprayer_ESP32 and Seeder_ESP32 (change both; check_shared_blocks.py compares them)
 // A whole number lo..hi in the request (only digits), else false
 static bool argNumber(const char* name, long lo, long hi, long& out)
 {
@@ -152,6 +155,7 @@ static bool captiveRedirect()
     server.send(302, "text/plain", "");
     return true;
 }
+// ==== end shared "request-helpers"
 
 // ---------------------------------------------------------------- web answers
 static void apiStatus()
@@ -204,6 +208,7 @@ static void apiStatus()
     for (uint8_t i = 0; i < MAX_TOOL_SECTIONS && i < cfg.toolSections; i++) { if (i) j += ","; j += String(cfg.sectionCm[i]); }
     j += "]}";
 
+    // ==== shared "status-log": the same in Sprayer_ESP32 and Seeder_ESP32 (change both; check_shared_blocks.py compares them)
     j += ",\"log\":[";
     bool first = true;
     for (uint8_t k = 0; k < 12; k++)
@@ -216,6 +221,7 @@ static void apiStatus()
     }
     j += "]}";
     sendJson(j);
+    // ==== end shared "status-log"
 }
 
 static void apiSettingsGet()
@@ -232,6 +238,7 @@ static void apiSettingsGet()
     sendJson(j);
 }
 
+// ==== shared "network-settings-post": the same in Sprayer_ESP32 and Seeder_ESP32 (change both; check_shared_blocks.py compares them)
 // "192.168.1" -> the three numbers; false when it is not three numbers 0-255
 static bool parseSubnet(const String& text, uint8_t out[3])
 {
@@ -269,7 +276,7 @@ static void apiWifiPost()
     s.ipLast = ipLast;
     cfg = s;
     settingsSave();
-    logEvent("Wi-Fi settings saved from the page, restarting");
+    logEvent("network settings saved from the page, restarting");
     sendJson("{\"ok\":true,\"restart\":true}");
     restartAtMs = millis() + 500;
 }
@@ -309,6 +316,7 @@ static void apiScan()
     scanState = -1;
     sendJson("{\"busy\":true}");
 }
+// ==== end shared "network-settings-post"
 
 static void apiCalibPost()
 {
@@ -366,6 +374,7 @@ static void apiTotalPost()
     sendJson("{\"ok\":true}");
 }
 
+// ==== shared "restart-update": the same in Sprayer_ESP32 and Seeder_ESP32 (change both; check_shared_blocks.py compares them)
 static void apiRestartPost()
 {
     if (!passwordOk()) return;
@@ -410,6 +419,7 @@ static void notFound()
     if (captiveRedirect()) return;
     server.send(404, "text/plain", "not found");
 }
+// ==== end shared "restart-update"
 
 void webStart()
 {
diff --git a/Sprayer/Sprayer_ESP32/zOutputs.ino b/Sprayer/Sprayer_ESP32/zOutputs.ino
index 5689d7b..3ef280d 100644
--- a/Sprayer/Sprayer_ESP32/zOutputs.ino
+++ b/Sprayer/Sprayer_ESP32/zOutputs.ino
@@ -13,6 +13,7 @@
 // RELAY_ON_HIGH (Sprayer_ESP32.ino) says how the relays of the chosen board close: on a HIGH pin
 // (ESP32_Relay_X8) or on a LOW pin (the usual relay modules). cfg.invertOutputs (PGN 238, byte 8
 // bit 0; the official module calls it isRelayActiveHigh) turns that round: 0 = as built, 1 = inverted.
+// ==== shared "relay-level": the same in Sprayer_ESP32 and Seeder_ESP32 (change both; check_shared_blocks.py compares them)
 // The program sends this setting at start-up and when the machine profile is loaded, so the
 // "relay active high" box in its machine settings normally stays unticked.
 
@@ -22,6 +23,7 @@ static int relayLevel(bool on)
     const bool drive = on != (cfg.invertOutputs != 0);
     return (drive == (RELAY_ON_HIGH != 0)) ? HIGH : LOW;
 }
+// ==== end shared "relay-level"
 
 static uint8_t raiseTimer = 0, lowerTimer = 0, lastTrigger = 0;
 
@@ -49,6 +51,7 @@ void outputsInit()
     }
 }
 
+// ==== shared "outputs": the same in Sprayer_ESP32 and Seeder_ESP32 (change both; check_shared_blocks.py compares them)
 // Everything off, whatever the polarity setting says (used before a restart or a program update)
 void outputsAllOff()
 {
@@ -117,4 +120,5 @@ void applyOutputs()
     relaysWrite(bits);
     relayBits = bits;
     sectionsOn = open;
+// ==== end shared "outputs"
 }
diff --git a/Sprayer/Sprayer_ESP32/zPgn.ino b/Sprayer/Sprayer_ESP32/zPgn.ino
index 4c4fae6..c2d2f2f 100644
--- a/Sprayer/Sprayer_ESP32/zPgn.ino
+++ b/Sprayer/Sprayer_ESP32/zPgn.ino
@@ -178,6 +178,7 @@ void sendAlarmMessage()
     lastMs = now;
 }
 
+// ==== shared "pgn-common-cases": the same in Sprayer_ESP32 and Seeder_ESP32 (change both; check_shared_blocks.py compares them)
 static void handlePgn(uint8_t pgn, const uint8_t* d, uint8_t dataLength, IPAddress from)
 {
     switch (pgn)
@@ -234,6 +235,7 @@ static void handlePgn(uint8_t pgn, const uint8_t* d, uint8_t dataLength, IPAddre
         logEvent("machine config from the program: lift %s, raise %u s, lower %u s, outputs %s",
                  cfg.hydEnable ? "on" : "off", cfg.raiseTime, cfg.lowerTime, cfg.invertOutputs ? "INVERTED (relay active high ticked)" : "normal");
         break;
+// ==== end shared "pgn-common-cases"
 
     case 236:                                               // output functions, 24 entries
         if (dataLength < 24) return;
@@ -263,6 +265,7 @@ static void handlePgn(uint8_t pgn, const uint8_t* d, uint8_t dataLength, IPAddre
         break;
     }
 
+    // ==== shared "pgn-subnet-receive": the same in Sprayer_ESP32 and Seeder_ESP32 (change both; check_shared_blocks.py compares them)
     case 201:                                               // subnet: save and restart with the new IP
         if (dataLength == 5 && d[5] == 201 && d[6] == 201)
         {
@@ -304,3 +307,4 @@ void udpPoll()
         handlePgn(pgn, rx, dataLength, udp.remoteIP());
     }
 }
+    // ==== end shared "pgn-subnet-receive"
diff --git a/Sprayer/Sprayer_ESP32/zSettings.ino b/Sprayer/Sprayer_ESP32/zSettings.ino
index ea8d9c5..7f931df 100644
--- a/Sprayer/Sprayer_ESP32/zSettings.ino
+++ b/Sprayer/Sprayer_ESP32/zSettings.ino
@@ -26,6 +26,7 @@ void settingsLoad()
 {
     Settings d;                                             // the defaults
     prefs.begin("sprayer", true);
+    // ==== shared "settings-wifi-load": the same in Sprayer_ESP32 and Seeder_ESP32 (change both; check_shared_blocks.py compares them)
     cfg.apSsid  = prefs.getString("apSsid", defaultApSsid());
     cfg.apPass  = prefs.getString("apPass", DEFAULT_AP_PASS);
     cfg.staOn   = prefs.getBool("staOn", false);
@@ -34,6 +35,7 @@ void settingsLoad()
     cfg.host    = prefs.getString("host", DEFAULT_HOST);
     if (prefs.getBytesLength("subnet") == 3) prefs.getBytes("subnet", cfg.subnet, 3);
     cfg.ipLast       = prefs.getUChar("ipLast", d.ipLast);
+    // ==== end shared "settings-wifi-load"
     cfg.raiseTime     = prefs.getUChar("raise", d.raiseTime);
     cfg.lowerTime     = prefs.getUChar("lower", d.lowerTime);
     cfg.hydEnable     = prefs.getUChar("hyd", d.hydEnable);
@@ -80,6 +82,7 @@ void settingsLoad()
 void settingsSave()
 {
     prefs.begin("sprayer", false);
+    // ==== shared "settings-wifi-save": the same in Sprayer_ESP32 and Seeder_ESP32 (change both; check_shared_blocks.py compares them)
     prefs.putString("apSsid", cfg.apSsid);
     prefs.putString("apPass", cfg.apPass);
     prefs.putBool("staOn", cfg.staOn);
@@ -88,6 +91,7 @@ void settingsSave()
     prefs.putString("host", cfg.host);
     prefs.putBytes("subnet", cfg.subnet, 3);
     prefs.putUChar("ipLast", cfg.ipLast);
+    // ==== end shared "settings-wifi-save"
     prefs.putUChar("raise", cfg.raiseTime);
     prefs.putUChar("lower", cfg.lowerTime);
     prefs.putUChar("hyd", cfg.hydEnable);
@@ -115,6 +119,7 @@ void settingsSave()
 
 // Only the Wi-Fi settings and the host name go back to the defaults (a forgotten password); the
 // program's config, the output functions and the calibration stay
+// ==== shared "settings-reset-wifi": the same in Sprayer_ESP32 and Seeder_ESP32 (change both; check_shared_blocks.py compares them)
 void settingsResetWifi()
 {
     cfg.apSsid  = defaultApSsid();
@@ -125,3 +130,4 @@ void settingsResetWifi()
     cfg.host    = DEFAULT_HOST;
     settingsSave();
 }
+// ==== end shared "settings-reset-wifi"