Working Beta Version Update for README, including the blog-post

KiCad/0004-DenshaBekutoru_v0.2/0004-DenshaBekutoru_v0.2.csv

@@ -0,0 +1,25 @@
+"Reference","Value","Datasheet","Footprint","Qty","DNP"
+"A1","Arduino_Pro_Mini_Socket_NoSPH_V2","https://docs.arduino.cc/retired/boards/arduino-pro-mini","arduino-library:Arduino_Pro_Mini_Socket_NoSPH_V2","1",""
+"C4","4.7µF","~","Capacitor_THT:CP_Axial_L10.0mm_D6.0mm_P15.00mm_Horizontal","1",""
+"C5","100nF","~","Capacitor_THT:C_Disc_D3.0mm_W1.6mm_P2.50mm","1",""
+"D1,D2","1N4148","https://assets.nexperia.com/documents/data-sheet/1N4148_1N4448.pdf","Diode_THT:D_DO-35_SOD27_P7.62mm_Horizontal","2",""
+"D3","1N5819","http://www.vishay.com/docs/88525/1n5817.pdf","Diode_THT:D_DO-41_SOD81_P10.16mm_Horizontal","1",""
+"D4","LED Green","~","LED_THT:LED_D3.0mm","1",""
+"D5","LED Yellow","~","LED_THT:LED_D3.0mm","1",""
+"D10","LED: HL_A.1","","LED_THT:LED_D5.0mm_Clear","1",""
+"D11","LED: HL_A.2","","LED_THT:LED_D5.0mm_Clear","1",""
+"D12","LED: HL_B.1","","LED_THT:LED_D5.0mm_Clear","1",""
+"D13","LED: HL_B.2","","LED_THT:LED_D5.0mm_Clear","1",""
+"J1","from Lego","~","Connector_PinHeader_2.54mm:PinHeader_1x04_P2.54mm_Vertical","1",""
+"J2","Headlight GND","~","Connector_PinSocket_2.54mm:PinSocket_1x04_P2.54mm_Vertical","1",""
+"J3","Headlight GND; A1,2/B1,2","~","Connector_PinSocket_2.54mm:PinSocket_1x05_P2.54mm_Vertical","1",""
+"J4","Headlight Test","~","Connector_PinHeader_2.54mm:PinHeader_1x05_P2.54mm_Horizontal","1",""
+"J5","I2C","~","Connector_PinHeader_2.54mm:PinHeader_1x03_P2.54mm_Vertical","1",""
+"J6","TX/RX","~","Connector_PinHeader_2.54mm:PinHeader_1x03_P2.54mm_Vertical","1",""
+"J7","Add. Lights","~","Connector_PinSocket_2.54mm:PinSocket_1x04_P2.54mm_Vertical","1",""
+"J8","LDR (~1MOhm) Option","~","Connector_PinHeader_2.54mm:PinHeader_1x02_P2.54mm_Vertical","1",""
+"R1,R2","1.5k","~","Resistor_THT:R_Axial_DIN0204_L3.6mm_D1.6mm_P5.08mm_Horizontal","2",""
+"R3,R4,R5,R6,R7,R8","220","~","Resistor_THT:R_Axial_DIN0204_L3.6mm_D1.6mm_P5.08mm_Horizontal","6",""
+"R9","10k","~","Resistor_THT:R_Axial_DIN0204_L3.6mm_D1.6mm_P5.08mm_Horizontal","1",""
+"RV1","1MOhm","~","Potentiometer_THT:Potentiometer_Piher_PT-10-V10_Vertical","1",""
+"U1,U2","PC817","http://www.soselectronic.cz/a_info/resource/d/pc817.pdf","Package_DIP:DIP-4_W7.62mm","2",""

KiCad/0004-DenshaBekutoru_v0.2/0004-DenshaBekutoru_v0.2.kicad_prl

@@ -1,7 +1,7 @@
 {
   "board": {
     "active_layer": 0,
-    "active_layer_preset": "",
+    "active_layer_preset": "All Layers",
     "auto_track_width": true,
     "hidden_netclasses": [],
     "hidden_nets": [],
@@ -64,7 +64,7 @@
       39,
       40
     ],
-    "visible_layers": "fffffff_fffffffe",
+    "visible_layers": "fffffff_ffffffff",
     "zone_display_mode": 0
   },
   "git": {

KiCad/0004-DenshaBekutoru_v0.2/0004-DenshaBekutoru_v0.2.kicad_pro

@@ -61,7 +61,7 @@
       "drc_exclusions": [
         "courtyards_overlap|116847500|113255000|4b518c68-cacc-4ba0-bdd7-4ed203d87dd8|c5b5c5e2-5bf5-406f-bc2c-791c87e4bd5a",
         "courtyards_overlap|116847500|116747500|4b518c68-cacc-4ba0-bdd7-4ed203d87dd8|ce87971b-d681-44d7-9fb7-23a15933148a",
-        "courtyards_overlap|126372500|116747500|4b518c68-cacc-4ba0-bdd7-4ed203d87dd8|1094a2e1-479d-4870-8b87-1411fc6da792",
+        "courtyards_overlap|126372500|116747500|1094a2e1-479d-4870-8b87-1411fc6da792|4b518c68-cacc-4ba0-bdd7-4ed203d87dd8",
         "courtyards_overlap|130322874|113255000|4b518c68-cacc-4ba0-bdd7-4ed203d87dd8|ee659d06-72c1-451a-8938-35a721a086e2"
       ],
       "meta": {
@@ -101,7 +101,7 @@
         "padstack": "warning",
         "pth_inside_courtyard": "ignore",
         "shorting_items": "error",
-        "silk_edge_clearance": "warning",
+        "silk_edge_clearance": "ignore",
         "silk_over_copper": "warning",
         "silk_overlap": "warning",
         "skew_out_of_range": "error",
@@ -507,7 +507,7 @@
   },
   "schematic": {
     "annotate_start_num": 0,
-    "bom_export_filename": "",
+    "bom_export_filename": "0004-DenshaBekutoru_v0.2.csv",
     "bom_fmt_presets": [],
     "bom_fmt_settings": {
       "field_delimiter": ",",
@@ -557,11 +557,35 @@
           "label": "DNP",
           "name": "${DNP}",
           "show": true
+        },
+        {
+          "group_by": false,
+          "label": "#",
+          "name": "${ITEM_NUMBER}",
+          "show": false
+        },
+        {
+          "group_by": false,
+          "label": "Sim.Device",
+          "name": "Sim.Device",
+          "show": false
+        },
+        {
+          "group_by": false,
+          "label": "Sim.Pins",
+          "name": "Sim.Pins",
+          "show": false
+        },
+        {
+          "group_by": false,
+          "label": "Description",
+          "name": "Description",
+          "show": false
         }
       ],
       "filter_string": "",
       "group_symbols": true,
-      "name": "Grouped By Value",
+      "name": "",
       "sort_asc": true,
       "sort_field": "Reference"
     },
@@ -594,7 +618,7 @@
     },
     "net_format_name": "Spice Model",
     "page_layout_descr_file": "",
-    "plot_directory": "./",
+    "plot_directory": "/home/tgohle/Desktop/git/ToGo-Lab/0004-DenshaBekutoru/KiCad/0004-DenshaBekutoru_v0.2/",
     "spice_current_sheet_as_root": false,
     "spice_external_command": "spice \"%I\"",
     "spice_model_current_sheet_as_root": true,

KiCad/0004-DenshaBekutoru_v0.2/0004-DenshaBekutoru_v0.2.kicad_sch

@@ -6,8 +6,8 @@
 	(paper "A4")
 	(title_block
 		(title "DenshaBekutoru 電車ベクトル (Train Vector)")
-		(date "2026-02-01")
+		(date "2026-03-08")
-		(rev "#003")
+		(rev "#005 1st bld.")
 		(company "ToGo-Lab")
 		(comment 1 "- https://togo-lab.io/")
 		(comment 2 "- Email: tgohle@togo-lab.io")
@@ -5902,9 +5902,9 @@
 		)
 		(uuid "0f47aaa2-d5fd-479c-9cd8-bfe8a8174c43")
 	)
-	(text "Detachable part of PCB (I),\nOption. If communication\nis needed.\n"
+	(text "Detachable part of PCB (I),\nOption. If communication\nis needed.\n\n! not tested\n"
 		(exclude_from_sim no)
-		(at 93.218 80.518 0)
+		(at 93.472 82.042 0)
 		(effects
 			(font
 				(size 1.27 1.27)
@@ -5913,9 +5913,9 @@
 		)
 		(uuid "13419e56-d967-466e-bc8e-26537e73dd52")
 	)
-	(text "Detachable part of PCB, Option\nIf used, control PWM (Light) by \n- LDR (dark ~ 1Mohm) or\n- Potentiometer 1Mohm (manually aqdjusted)"
+	(text "Detachable part of PCB, Option\nIf used, control PWM (Light) by \n- LDR (dark ~ 1Mohm) or\n- Potentiometer 1Mohm (manually aqdjusted)\n\n! Not tested"
 		(exclude_from_sim no)
-		(at 78.486 171.958 0)
+		(at 78.232 170.18 0)
 		(effects
 			(font
 				(size 1.27 1.27)
@@ -5935,7 +5935,7 @@
 		)
 		(uuid "2f37a28e-8a64-4672-a892-5431464a2db8")
 	)
-	(text "PWM LED drive – Arduino Pro Mini (ATmega328P)\n- PWM pins used: D3 (Timer2, 8-bit) and D9 (Timer1, 16-bit)\n- Control via analogWrite() → 0–255 on both timers (no practical difference for LEDs)\n- Each PWM pin drives 2× white LEDs in parallel, each LED with its own 220 Ω resistor\n- Approx. current per LED ≈ 7–8 mA, per pin ≈ 15 mA → safe for MCU\n- D0/D1 (TX/RX) free for later communication\n- Timer0 untouched → millis()/delay() unaffected\n- No Servo / tone / IR usage planned → no timer conflicts expected\n- Remember, Unsused D/A Connectors: Unconnected (no Pullup), but:\n   Digital ones: \"pinMode(pin, INPUT_PULLUP);\" and Ax: nothing."
+	(text "PWM LED drive – Arduino Pro Mini (ATmega328P)\n- PWM pins used: D3 (Timer2, 8-bit) and D9 (Timer1, 16-bit)\n- Control via analogWrite() → 0–255 on both timers (no practical difference for LEDs)\n- Each PWM pin drives 2× white LEDs in parallel, each LED with its own 220 Ω resistor\n- Approx. current per LED ≈ 7–8 mA, per pin ≈ 15 mA → safe for MCU\n- D0/D1 (TX/RX) free for later communication\n- Timer0 untouched → millis()/delay() unaffected\n- No Servo / tone / IR usage planned → no timer conflicts expected\n- Remember, Unsused D/A Connectors: Unconnected (no Pullup), but:\n   Digital ones: \"pinMode(pin, INPUT_PULLUP);\" and Ax: nothing.\n- all R smallest type (1/4W), due small footprint"
 		(exclude_from_sim no)
 		(at 128.778 49.53 0)
 		(effects
@@ -5967,7 +5967,7 @@
 		)
 		(uuid "9433f522-95dc-40eb-b260-abe7c4605d43")
 	)
-	(text "Detachable part of PCB (I)\nAdditional PWM Lights\n- Timer1, (D9): D10\n- Timer2, (D3): D11\n! Don't forget Resistors"
+	(text "Detachable part of PCB (I)\nAdditional PWM Lights\n- Timer1, (D9): D10\n- Timer2, (D3): D11\n! Don't forget Resistors\n\n! Not tested"
 		(exclude_from_sim no)
 		(at 246.38 66.04 0)
 		(effects
@@ -7071,7 +7071,7 @@
 				)
 			)
 		)
-		(property "Value" "1.8k"
+		(property "Value" "1.5k"
 			(at 58.42 118.11 90)
 			(effects
 				(font
@@ -7204,7 +7204,7 @@
 				)
 			)
 		)
-		(property "Value" "1.8k"
+		(property "Value" "1.5k"
 			(at 58.42 106.68 90)
 			(effects
 				(font

KiCad/0004-DenshaBekutoru_v0.2/report.txt

@@ -1,31 +0,0 @@
-Info: Processing symbol 'J7:Connector_PinSocket_2.54mm:PinSocket_1x04_P2.54mm_Vertical'.
-Info: Processing symbol 'U2:Package_DIP:DIP-4_W7.62mm'.
-Info: Processing symbol 'U1:Package_DIP:DIP-4_W7.62mm'.
-Info: Processing symbol 'RV1:Potentiometer_THT:Potentiometer_Piher_PT-10-V10_Vertical'.
-Info: Processing symbol 'R9:Resistor_THT:R_Axial_DIN0204_L3.6mm_D1.6mm_P1.90mm_Vertical'.
-Info: Processing symbol 'R8:Resistor_THT:R_Axial_DIN0204_L3.6mm_D1.6mm_P1.90mm_Vertical'.
-Info: Processing symbol 'R7:Resistor_THT:R_Axial_DIN0204_L3.6mm_D1.6mm_P1.90mm_Vertical'.
-Info: Processing symbol 'R6:Resistor_THT:R_Axial_DIN0204_L3.6mm_D1.6mm_P1.90mm_Vertical'.
-Info: Processing symbol 'R5:Resistor_THT:R_Axial_DIN0204_L3.6mm_D1.6mm_P1.90mm_Vertical'.
-Info: Processing symbol 'R4:Resistor_THT:R_Axial_DIN0204_L3.6mm_D1.6mm_P5.08mm_Horizontal'.
-Info: Processing symbol 'R3:Resistor_THT:R_Axial_DIN0204_L3.6mm_D1.6mm_P5.08mm_Horizontal'.
-Info: Processing symbol 'R2:Resistor_THT:R_Axial_DIN0204_L3.6mm_D1.6mm_P5.08mm_Horizontal'.
-Info: Processing symbol 'R1:Resistor_THT:R_Axial_DIN0204_L3.6mm_D1.6mm_P5.08mm_Horizontal'.
-Info: Processing symbol 'J8:Connector_PinHeader_2.54mm:PinHeader_1x02_P2.54mm_Vertical'.
-Info: Processing symbol 'A1:arduino-library:Arduino_Pro_Mini_Socket_NoSPH_V2'.
-Info: Processing symbol 'J6:Connector_JST:JST_PH_B3B-PH-K_1x03_P2.00mm_Vertical'.
-Info: Processing symbol 'J5:Connector_JST:JST_PH_B3B-PH-K_1x03_P2.00mm_Vertical'.
-Info: Processing symbol 'J4:Connector_PinSocket_2.54mm:PinSocket_1x05_P2.54mm_Vertical'.
-Info: Processing symbol 'J3:Connector_PinSocket_2.54mm:PinSocket_1x05_P2.54mm_Horizontal'.
-Info: Processing symbol 'J2:Connector_PinSocket_2.54mm:PinSocket_1x04_P2.54mm_Vertical'.
-Info: Processing symbol 'J1:Connector_PinHeader_2.54mm:PinHeader_1x04_P2.54mm_Horizontal'.
-Info: Processing symbol 'D5:LED_THT:LED_D1.8mm_W3.3mm_H2.4mm'.
-Info: Processing symbol 'D4:LED_THT:LED_D1.8mm_W3.3mm_H2.4mm'.
-Info: Processing symbol 'D3:Diode_THT:D_DO-41_SOD81_P10.16mm_Horizontal'.
-Info: Processing symbol 'D2:Diode_THT:D_DO-35_SOD27_P7.62mm_Horizontal'.
-Info: Processing symbol 'D1:Diode_THT:D_DO-35_SOD27_P7.62mm_Horizontal'.
-Info: Processing symbol 'C5:Capacitor_THT:C_Disc_D3.0mm_W1.6mm_P2.50mm'.
-Info: Processing symbol 'C4:Capacitor_THT:CP_Axial_L10.0mm_D6.0mm_P15.00mm_Horizontal'.
-
-
-Info: Total warnings: 0, errors: 0.

README.md

@@ -1,12 +1,90 @@
-# DenshaBekutoru - Model Train Direction Sensor
+# 電車ベクトル (DenshaBekutoru)  
 
-Get **direction** and **speed** from motor power signals.  
+## Model Train Direction Sensor
-Target use case: **model trains**.
 
-- Detects polarity (+/–) to identify train direction  
+DenshaBekutoru is a small controller board for brick-built model locomotives.
-- Measures pulse width to calculate speed (% of maximum)  
-- Implemented with optocouplers and a state machine  
-- As small as possible, but I hope no SMD (beginner friendly)
 
-Project is in an early stage. Currently running tests on target hardware.  
+The target use case is: read the motor power signals, detect the current driving direction, and switch the headlights accordingly. The software is also prepared to derive speed information from the motor signal behaviour.
-More information and documentation will follow.
+
+This project is built around one practical problem: the motor is driven from an H-bridge, so the signal is noisy, polarity changes are not “clean logic”, and inductive spikes make direct evaluation difficult.
+
+## What it does
+
+- detects train direction from the motor power signal
+- evaluates two processed motor-side signals via analogue inputs
+- switches the front / rear lights according to direction
+- keeps the last valid direction if the train stops or the signal becomes unclear
+- is designed as small as possible for installation in brick-built locomotives
+
+## Technical approach
+
+The current version is built around:
+
+- optocoupler-based input isolation and signal conditioning
+- Arduino Pro Mini 5V as controller
+- software averaging of analogue inputs
+- startup calibration to adapt to different controllers and builds
+- threshold + hysteresis logic
+- simple state machine with direction memory
+- PWM-capable output pins for possible later LED dimming
+
+The main idea is not to read one raw signal and react immediately.  
+The idea is to turn a noisy motor signal into a stable direction decision.
+
+## Current status
+
+**Version 2 (beta) is built and working.**
+
+Current state:
+
+- [x] schematic finished
+- [x] PCB finished
+- [x] firmware finished for the current beta state
+- [x] three PCBs built and tested
+- [x] first boards handed over for real-life testing in a model railway club
+- [ ] Feedback and what to improve
+
+## Design goals
+
+- as small as possible
+- beginner-friendly where possible
+- no SMD if it can reasonably be avoided
+- easy to reproduce later as a DIY kit
+- modular PCB concept with main section, future-option section, and test section
+
+## Repository content
+
+Typical content of this repository:
+
+- `KiCad/` – schematic and PCB files
+- `firmware/` – Arduino test and controller software
+- documentation and pictures will be added step by step
+
+## Project status note
+
+This is still a beta project.
+
+The current hardware and software already work, but testing on real locomotives is still ongoing.  
+The next version will depend on real-life feedback from actual use.
+
+Possible next steps:
+
+- verify behaviour with different motor controllers
+- check robustness in real train builds
+- improve wiring / connector handling
+- finalise optional features like LED dimming
+- prepare a first “official” DIY kit version
+
+## Blog / documentation
+
+- Project overview:  https://togo-lab.io/?p=223
+- Hardware description:  https://togo-lab.io/?p=233
+- Software description:  https://togo-lab.io/?p=243
+
+## Short summary
+
+DenshaBekutoru is a small Arduino-based direction sensor for brick-built model trains.
+
+It reads the noisy motor signal from an H-bridge-driven setup, isolates and evaluates it, and switches the headlights automatically.
+
+The current beta version is working and now entering real-life testing.

firmware/ArduinoTest/DenshaBekutoru-0004_Version-0-2_ProMini_PCB2026-2_V01/DenshaBekutoru-0004_Version-0-2_ProMini_PCB2026-2_V01.ino

@@ -0,0 +1,287 @@
+/*
+  0004_DenshaBekutoru – 1st Version PCB
+ 
+  PCB Version      : 2026/02 (Order F016895)
+  Target dev board : Arduino Pro Mini 5V / 16 MHz (ATmega328P)
+  
+  ----------------------------------------------------------------------------
+  State machine (direction memory) + Hysteresis (Version A)
+  ----------------------------------------------------------------------------
+  We use two thresholds:
+    T_hold  (smaller): below -> treat as neutral and HOLD state
+    T_enter (larger) : above -> allow direction change (set by sign)
+
+  Behavior:
+    If |diff| <= T_hold  : hold direction
+    If |diff| >= T_enter : set direction by sign
+    Else (between)       : hold direction
+
+  Presets (implemented as multipliers of the calibrated VdiffThreshold):
+    T_hold  = 1.0 * VdiffThreshold
+    T_enter = 2.0 * VdiffThreshold
+
+  Inputs derived from v1, v2: diff = v1 - v2
+*/
+
+const unsigned long SAMPLE_WINDOW_MS = 100;   // averaging window per measurement
+const unsigned long SAMPLE_DELAY_US  = 500;   // delay between ADC samples (~2 kHz)
+
+const uint8_t ADC_PIN_1 = A0;  // Pro Mini A0 -> (PCB dependend!)
+const uint8_t ADC_PIN_2 = A1;  // Pro Mini A1 -> (PCB dependend")
+
+// Direction LEDs (avoid D0/D1 because you may want RX/TX later)
+const uint8_t LED_DIR1_PIN = 3;  // D3
+const uint8_t LED_DIR2_PIN = 9;  // D9
+
+const unsigned int LED_BLINK_ON_MS  = 150;
+const unsigned int LED_BLINK_OFF_MS = 150;
+
+// Serial output control (0 = no output, 1 = output)
+bool SerialOutputAllow = true;
+
+// ---- Calibration parameters ----
+const uint16_t AverageRepeat = 100;          // number of init measurements
+const float VdiffThresholdMargin = 1.50f;    // multiplier (e.g., 1.5 = +50% margin)
+const float VdiffThresholdMinVolts = 0.03f;  // floor in volts
+
+// ---- Hysteresis presets (multipliers of VdiffThreshold) ----
+const float THOLD_MULT  = 1.0f;  // T_hold  = THOLD_MULT  * VdiffThreshold
+const float TENTER_MULT = 2.0f;  // T_enter = TENTER_MULT * VdiffThreshold
+
+// Globals: latest measured averaged voltages
+float v1 = 0.0f;
+float v2 = 0.0f;
+
+// Calibration globals
+float VdiffBaseline = 0.0f;   // median(|V1-V2|) measured at boot (no movement)
+float VdiffThreshold = 0.0f;  // calibrated base threshold (used to derive T_hold/T_enter)
+
+// Hysteresis thresholds (derived once after calibration)
+float T_hold  = 0.0f;
+float T_enter = 0.0f;
+
+// Direction encoding:
+// 0 = NONE, 2 = DIR1, 3 = DIR2
+byte direction = 0;
+
+static inline float absf(float x) { return (x >= 0.0f) ? x : -x; }
+static inline float maxf(float a, float b) { return (a > b) ? a : b; }
+
+// -----------------------------------------------------------------------------
+// LED helpers
+// -----------------------------------------------------------------------------
+static void blinkLED(uint8_t pin, uint8_t times)
+{
+  for (uint8_t i = 0; i < times; i++) {
+    digitalWrite(pin, HIGH);
+    delay(LED_BLINK_ON_MS);
+    digitalWrite(pin, LOW);
+    delay(LED_BLINK_OFF_MS);
+  }
+}
+
+static void initBlinkSequence()
+{
+  // LED at Output 2 blinks 2 times
+  blinkLED(LED_DIR1_PIN, 2);
+
+  // LED at Output 3 blinks 3 times
+  blinkLED(LED_DIR2_PIN, 3);
+}
+
+static void applyDirectionOutputs()
+{
+  digitalWrite(LED_DIR1_PIN, LOW);
+  digitalWrite(LED_DIR2_PIN, LOW);
+
+  if (direction == 2) {
+    digitalWrite(LED_DIR1_PIN, HIGH);
+  } else if (direction == 3) {
+    digitalWrite(LED_DIR2_PIN, HIGH);
+  }
+}
+
+// -----------------------------------------------------------------------------
+// Measurement
+// -----------------------------------------------------------------------------
+static void measureAveragedVoltages()
+{
+  unsigned long startTime = millis();
+
+  unsigned long sum1 = 0;
+  unsigned long sum2 = 0;
+  unsigned long samples = 0;
+
+  while (millis() - startTime < SAMPLE_WINDOW_MS) {
+    sum1 += analogRead(ADC_PIN_1);
+    sum2 += analogRead(ADC_PIN_2);
+    samples++;
+    delayMicroseconds(SAMPLE_DELAY_US);
+  }
+
+  float avg1 = (float)sum1 / samples;
+  float avg2 = (float)sum2 / samples;
+
+  // Convert ADC value to voltage (default analog reference = Vcc ~ 5V)
+  v1 = avg1 * (5.0f / 1023.0f);
+  v2 = avg2 * (5.0f / 1023.0f);
+}
+
+// -----------------------------------------------------------------------------
+// Median helpers (for calibration)
+// -----------------------------------------------------------------------------
+static void sortFloatArray(float *a, uint16_t n)
+{
+  // Insertion sort (n=100 is small, OK)
+  for (uint16_t i = 1; i < n; i++) {
+    float key = a[i];
+    int16_t j = (int16_t)i - 1;
+    while (j >= 0 && a[j] > key) {
+      a[j + 1] = a[j];
+      j--;
+    }
+    a[j + 1] = key;
+  }
+}
+
+static float medianOfSortedFloatArray(const float *a, uint16_t n)
+{
+  if (n == 0) return 0.0f;
+  if (n & 1) {
+    return a[n / 2];
+  } else {
+    return (a[(n / 2) - 1] + a[n / 2]) * 0.5f;
+  }
+}
+
+// Calibrate baseline + VdiffThreshold once at boot/reset
+static void calibrateVdiffThreshold(uint16_t averageRepeat)
+{
+  if (averageRepeat < 1) averageRepeat = 1;
+  if (averageRepeat > 200) averageRepeat = 200; // RAM safety cap
+
+  float diffs[200];
+
+  for (uint16_t i = 0; i < averageRepeat; i++) {
+    measureAveragedVoltages();
+    diffs[i] = absf(v1 - v2); // baseline mismatch sample
+  }
+
+  sortFloatArray(diffs, averageRepeat);
+  VdiffBaseline = medianOfSortedFloatArray(diffs, averageRepeat);
+
+  // Calibrated base threshold with margin + floor
+  VdiffThreshold = maxf(VdiffBaseline * VdiffThresholdMargin, VdiffThresholdMinVolts);
+
+  // Derive hysteresis thresholds (Version A)
+  T_hold  = THOLD_MULT  * VdiffThreshold;
+  T_enter = TENTER_MULT * VdiffThreshold;
+}
+
+// -----------------------------------------------------------------------------
+// State machine with hysteresis (Version A)
+// -----------------------------------------------------------------------------
+static void updateDirectionFromVoltages()
+{
+  const float diff = v1 - v2;
+  const float absDiff = absf(diff);
+
+  // 1) Neutral region: HOLD
+  if (absDiff <= T_hold) {
+    return;
+  }
+
+  // 2) Strong region: allow direction change
+  if (absDiff >= T_enter) {
+    direction = (diff > 0.0f) ? (byte)2 : (byte)3;
+    return;
+  }
+
+  // 3) Deadband between T_hold and T_enter: HOLD
+  return;
+}
+
+// -----------------------------------------------------------------------------
+// Serial output
+// -----------------------------------------------------------------------------
+static void serialPrintAll()
+{
+  if (!SerialOutputAllow) return;
+
+  Serial.print("A2 for PB3  XTAL1, Pin2: ");
+  Serial.print(v1, 3);
+  Serial.print(" V   |   ");
+
+  Serial.print("A3 for PB4 XTAL2, Pin3: ");
+  Serial.print(v2, 3);
+  Serial.print(" V   |   ");
+
+  Serial.print("|V1-V2|: ");
+  Serial.print(absf(v1 - v2), 3);
+  Serial.print(" V   |   ");
+
+  Serial.print("VdiffBaseline: ");
+  Serial.print(VdiffBaseline, 3);
+  Serial.print(" V   |   ");
+
+  Serial.print("VdiffThreshold: ");
+  Serial.print(VdiffThreshold, 3);
+  Serial.print(" V   |   ");
+
+  Serial.print("T_hold: ");
+  Serial.print(T_hold, 3);
+  Serial.print(" V   |   ");
+
+  Serial.print("T_enter: ");
+  Serial.print(T_enter, 3);
+  Serial.print(" V   |   ");
+
+  Serial.print("direction: ");
+  Serial.println(direction);
+}
+
+// -----------------------------------------------------------------------------
+// Arduino entry points
+// -----------------------------------------------------------------------------
+void setup() {
+  Serial.begin(115200);
+
+  pinMode(ADC_PIN_1, INPUT);
+  pinMode(ADC_PIN_2, INPUT);
+
+  pinMode(LED_DIR1_PIN, OUTPUT);
+  pinMode(LED_DIR2_PIN, OUTPUT);
+
+  // Initial calibration (assumes no movement)
+  calibrateVdiffThreshold(AverageRepeat);
+
+  // Init blink sequence: 2x on D2, 3x on D3
+  initBlinkSequence();
+
+  // One measurement for initial display + initial direction
+  measureAveragedVoltages();
+  updateDirectionFromVoltages();
+  applyDirectionOutputs();
+
+  if (SerialOutputAllow) {
+    Serial.println("=== DenshaBekutoru Optocoupler Average Test (Arduino Pro Mini 5V/16MHz) ===");
+    Serial.print("AverageRepeat: ");
+    Serial.println(AverageRepeat);
+    Serial.print("THOLD_MULT: ");
+    Serial.print(THOLD_MULT, 2);
+    Serial.print("   TENTER_MULT: ");
+    Serial.println(TENTER_MULT, 2);
+  }
+
+  serialPrintAll();
+}
+
+void loop() {
+  measureAveragedVoltages();
+  updateDirectionFromVoltages();
+  applyDirectionOutputs();
+
+  serialPrintAll();
+
+  delay(300);
+}