🏭 Rejection Bin Interlocking System

ESP32-Based Industrial Part Rejection control and Rejection count Logging system

📖 Overview

This project implements an ESP32-based industrial rejection bin interlocking system. It stops the machine when a reject is triggered, waits for the operator to confirm the rejected part in the bin, and then resumes production after the confirmation sequence is validated.

Key Features:

Three detection slots with dual-sensor confirmation (A→B sequence)
Hybrid storage system using EEPROM for critical state and SPIFFS for session history
Boot-based session tracking with a separate count for each power cycle
Lifetime reject count (persists forever)
Automatic file management that keeps the last 100 boot sessions
State persistence across power cycles
Visual/audio alerts for operator awareness
500 ms confirmation beep for sensor events and alerts

🆕 What's New in v4.0

🛡️ Runtime Hardening (Current Build)

The current firmware includes additional runtime protection features:

Non-blocking serial command parser to avoid loop stalls
I2C retry logic for PCF8574 input/output transactions
I2C fail-safe lock after repeated consecutive bus failures
Button debounce filtering for AUTO/REJECT inputs
Reduced web heap churn through response pre-allocation and streaming

These changes are aimed at long-run stability in production environments.

🚀 Hybrid Storage Architecture (EEPROM + SPIFFS)

EEPROM Storage (Fast & Reliable):

Data	Purpose	Write Speed
`machine_mode`	AUTO/REJECT state (critical)	~3-4ms
`lifetime_count`	Total rejects (never resets)	~3-4ms
`boot_number`	Power cycles (increments per boot)	~3-4ms

SPIFFS Storage (Historical Data):

File Name	Purpose	Retention
`/start_X.txt`	Rejects per boot session	Last 100 boots
`/version.txt`	Firmware version tracking	Current version

Why Hybrid Storage?

✅ 10x faster writes - EEPROM writes in 3-4ms vs SPIFFS 50-100ms
✅ Power-loss safe - EEPROM writes are atomic and instant
✅ Better wear leveling - EEPROM has ~100,000 write cycles vs SPIFFS flash ~10,000
✅ Reliable state recovery - Critical data survives sudden power loss
✅ Historical tracking - SPIFFS still maintains session logs for analysis

Storage Architecture

EEPROM (512 bytes)
   Address 0-1   : Magic number (0xABCD)
   Address 2     : machine_mode (AUTO / REJECT)
   Address 3-6   : lifetime_count
   Address 7-10  : boot_number
   Address 11-12 : firmware version

SPIFFS (~1.3 MB available on the selected partition)
   /version.txt  : Firmware version tracking
   /start_1.txt  : Boot 1 session log
   /start_2.txt  : Boot 2 session log
   ...
   /start_100.txt: Boot 100 session log

Automatic File Management

Creates new session file on each ESP32 restart
Tracks rejects separately for each boot session
Batch deletes old sessions at boot 101, 201, 301... (keeps last 100)
Space efficient: ~1 KB for 100 session files

Example Timeline

Boot 1:   start_1.txt (5 rejects)    Total: 5
Boot 2:   start_2.txt (3 rejects)    Total: 8
...
Boot 100: start_100.txt (2 rejects)  Total: 5,243
Boot 101: ⚡ DELETE start_1 to start_100
          start_101.txt (7 rejects)  Total: 5,250

📚 Libraries Used

Library Name	Purpose
`Wire.h`	I2C communication with PCF8574 expanders
`EEPROM.h`	Non-volatile storage for critical data
`SPIFFS.h`	Internal flash file system for session logs
`FS.h`	Base file system operations
`WiFi.h`	WiFi AP mode for web server access
`WebServer.h`	HTTP web server for remote monitoring

🧰 Hardware Components

Component	Quantity	Description
ESP32 DevKit	1	Main microcontroller (1.3 MB SPIFFS + 512B EEPROM)
PCF8574 I/O Expander	2	I2C input/output expansion (0x25, 0x26)
Push Button (AUTO)	1	Start machine operation
Push Button (REJECT)	1	Stop machine and enter reject mode
Proximity Sensor	6	Part detection (2 sensors per slot: A & B)
Relay Module	1	Controls machine AUTO signal to PLC
LED (Machine ON)	1	GREEN LED - indicates when machine is running
LED + Buzzer (Alert)	1	RED LED/Buzzer - active during reject mode

📂 Project Files Reference

Header Files (`.h`)

File	Purpose
`config.h`	Pin definitions, I2C addresses, global variables, constants
`eeprom_operations.h`	EEPROM management for machine_mode, boot, lifetime count
`file_operations.h`	SPIFFS init, session file management, batch deletion
`io_operations.h`	PCF8574 read/write, output control, beep timing
`process.h`	Button event handlers (AUTO, REJECT)
`reject.h`	Dual-sensor slot detection, rejection sequence handling
`serial_cmd.h`	Serial command interface (LIST, READ, HELP, RST)
`web_server.h`	WiFi AP mode, web dashboard, file management interface

Main Program

File	Purpose
`r_bin_interlock_sys.ino`	Main program loop, initialization sequence, input polling

🔌 Pin Mapping

ESP32 Hardware Pins

Pin	Function	Description
GPIO21	SDA	I2C data line
GPIO22	SCL	I2C clock line

PCF8574 #1 (Address 0x25) - Input Expander

Pin	Function	Description
0	SLOT3_B	Slot 3 Sensor B (back)
1	SLOT3_A	Slot 3 Sensor A (front)
2	SLOT2_B	Slot 2 Sensor B (back)
3	SLOT2_A	Slot 2 Sensor A (front)
4	SLOT1_B	Slot 1 Sensor B (back)
5	SLOT1_A	Slot 1 Sensor A (front)
6	BTN_REJECT	REJECT/E-STOP button input
7	BTN_AUTO	AUTO button input

PCF8574 #2 (Address 0x26) - Output Expander

Pin	Function	Description
0	RELAY_AUTO	AUTO relay output to PLC
1	LED_MACHINE_ON	GREEN LED - Machine running
2	BUZZER_LED	RED LED + Buzzer (500ms beeps)
3-7	UNUSED	Available for future expansion

🛠️ Software Requirements

Software/Tool	Version	Description
Arduino IDE	2.x+	Development environment for ESP32 programming
ESP32 Board Package	2.x-3.x	ESP32 board support for Arduino IDE
Serial Monitor	Any	Debug and monitor system events (115200 baud)
WiFi Client (Browser)	Any	Access web dashboard (Chrome, Firefox, Safari, Edge, etc.)

⚙️ System Operation Modes

AUTO Mode (Normal Production)

✓ Machine relay: ON (energized)
✓ GREEN LED: ON (Machine running indicator)
✓ Alerts: OFF (silent operation)
✓ Monitoring: Sensors active, waiting for part detection
✓ Serial Output: Normal operation messages

REJECT Mode (Waiting for Part Confirmation)

⚠ Machine relay: OFF (de-energized, PLC signal halted)
⚠ RED LED/Buzzer: ACTIVE (500ms beeps on sensor triggers)
⚠ GREEN LED: OFF
⚠ System State: Locked, waiting for part confirmation
⚠ AUTO button: IGNORED until part confirmed
⚠ Serial Output: Alert and waiting messages

📊 Part Detection Sequence

Valid Rejection Workflow

1. REJECT button pressed (operator triggers rejection)
   ↓ Machine stops, enters REJECT mode
   ↓ Machine mode saved to EEPROM (instant, power-safe)
   
2. Operator places rejected part in bin
   ↓ Part enters slot (Sensor A triggers)
   ↓ BEEP notification (500ms)
   
3. Part fully seats (Sensor B triggers)
   ↓ BEEP notification (500ms)
   
4. A→B sequence confirmed
   ↓ Machine mode = AUTO (saved to EEPROM)
   ↓ Continuous anti-cheat monitoring remains active
   
5. The part is counted when the next cycle is finalized
   ↓ Lifetime count incremented (saved to EEPROM)
   ↓ Session count incremented (saved to SPIFFS)
   ↓ Ready for the next operator action

Cheat Detection (Anti-Removal)

While continuous monitoring is active after A→B confirmation:
  - If Sensor A triggers again after Sensor B (B→A) = CHEATING DETECTED
  - Count NOT incremented
  - Machine stops immediately
  - System enters REJECT mode (saved to EEPROM)
  - Triple beep alert (emergency notification)
  - Part must be re-confirmed in bin before restart

I2C Fail-safe Behavior

If I2C communication repeatedly fails:
   - Each read/write is retried (I2C_RETRY_COUNT)
   - Consecutive failures are counted
   - At threshold (I2C_FAILSAFE_THRESHOLD), system enters fail-safe
   - Machine is forced to REJECT mode
   - Relay is turned OFF
   - Mode is persisted to EEPROM
   - Triple beep alert is triggered

💾 Data Persistence Architecture

EEPROM Storage (Critical Data)

Address	Data	Size	Purpose	Write Frequency
0-1	Magic Number	2 bytes	First boot detection (0xABCD)	Once (first boot)
2	machine_mode	1 byte	AUTO/REJECT state	Every reject cycle
3-6	lifetime_count	4 bytes	Total rejects (never resets)	Every part confirmation
7-10	boot_number	4 bytes	Power cycles	Every boot
11-12	firmware version	2 bytes	Detect firmware changes	On firmware update

EEPROM Characteristics:

Write time: 3-4ms (instant)
Write cycles: ~100,000 per cell
Power-loss safe: Atomic writes
Survives: Power glitches, brown-outs, sudden shutdowns

SPIFFS Storage (Session History)

File Name	Purpose	Retention	Contents
`/start_X.txt`	Reject count per boot session	Last 100 boots	Single integer
`/version.txt`	Firmware version tracking	Current version	Single integer

SPIFFS Characteristics:

Write time: 50-100ms
Total capacity: 1.3 MB
Session logs: ~10 bytes each
Batch management: Auto-deletes old files

Automatic File Management

Session File Organization:

Each ESP32 restart creates new /start_X.txt file
Tracks rejects separately for each boot session
Batch deletion triggers every 100 boots (at boot 101, 201, 301...)
Always maintains last 100 session files

Example Timeline:

Boot 1:   /start_1.txt (5 rejects)     Lifetime Total: 5 (EEPROM)
Boot 2:   /start_2.txt (3 rejects)     Lifetime Total: 8 (EEPROM)
Boot 3:   /start_3.txt (7 rejects)     Lifetime Total: 15 (EEPROM)
...
Boot 100: /start_100.txt (2 rejects)   Lifetime Total: 5,243 (EEPROM)
Boot 101: ⚡ BATCH DELETE: /start_1.txt through /start_100.txt removed
          /start_101.txt (0 rejects)   Lifetime Total: 5,243 (EEPROM)
Boot 102: /start_102.txt (4 rejects)   Lifetime Total: 5,247 (EEPROM)

Power Loss Recovery

Scenario 1: Power loss during reject cycle

✅ machine_mode saved in EEPROM before power loss
✅ System boots in REJECT mode
✅ Operator must confirm part in bin
✅ No data corruption possible

Scenario 2: Power loss during count increment

If power lost BEFORE EEPROM write:
  ⚠ That one reject might not be counted (rare)
  
If power lost AFTER EEPROM write:
  ✅ Count is saved (typical case)
  ✅ System recovers correctly

Storage Capacity

Parameter	Value
EEPROM size	512 bytes
EEPROM used	13 bytes (3% utilization)
Session file size	~10 bytes per file
Max session files	100 (configurable in `config.h`)
Total SPIFFS used	~1 KB for all session data
SPIFFS capacity	1.3 MB
Space utilization	0.08% (extremely efficient)

🌐 Web Server & WiFi

WiFi AP Configuration

Network Name (SSID): RejectionBin_AP
Password:            rejectionbin
IP Address:          192.168.1.21
Gateway:             192.168.1.21
Subnet:              255.255.255.0

Web Dashboard Features

URL: http://192.168.1.21

Routes:
├── /                 Dashboard
├── /sessions         All boot session files
├── /files            All files currently in SPIFFS
├── /view?file=...    View a file in the browser
├── /download?file=... Download a single file
└── /downloadall      Export all available data as plain text

Web Dashboard Display

Current boot number stored in EEPROM
Current session reject count stored in the current /start_X.txt
Lifetime total rejects stored in EEPROM
Machine mode stored in EEPROM (REJECT / AUTO)
Recent session history and file browser
File download functionality

Important note

The dashboard shows placeholders for /boot_number.txt, /total_count.txt, and /state.txt in the code, but those files are not created by the firmware. The actual persistent files are /version.txt and the /start_X.txt session logs.

🖥️ Serial Command Interface

Serial Port Settings

Baud Rate: 115200
Data Bits: 8
Stop Bits: 1
Parity:    None

Available Serial Commands

Command	Parameters	Purpose	Example
`LIST`	None	Display EEPROM values and SPIFFS files	`LIST`
`READ`	`<file_path>`	Display specific file contents	`READ /start_1.txt`
`RST`	None	Restart ESP32	`RST`
`HELP`	None	Show the help menu and AP details	`HELP`

Serial handling note: Command parsing is non-blocking and line-buffered for better loop responsiveness.

Serial Output During Operation

Boot Sequence:

WELCOME ESP32 : REJECTION BIN INTERLOCKING SYSTEM
=== EEPROM INIT ===
EEPROM already initialized
[EEPROM] Boot Number: 25
[EEPROM] Lifetime Count: 1847
[EEPROM] Machine Mode: AUTO
===================
=== SPIFFS INIT ===
SPIFFS Mounted successfully
Total: 1.30 MB | Used: 0.05 MB | Free: 1.25 MB
===================
[SPIFFS] Created session file: /start_25.txt
-------------SYSTEM STATUS-------------
Boot Number:          25
Session Count:        0
Lifetime rejection:   1847
Machine Mode:         AUTO
----------------------------------------
SYSTEM READY
Press AUTO button to start machine

During Operation:

AUTO MODE - MACHINE RUNNING
[SENSOR] Slot 1A detected - waiting for 1B...
[SENSOR] Slot 1B detected - A→B sequence complete
[EEPROM] Saved Machine Mode: AUTO
[MONITORING] Started continuous monitoring for Slot 1
[MONITORING] Part confirmed in Slot 1
Part confirmed in Slot 1 (no B→A removal detected)
Session Count (Boot #25): 1
Lifetime Total Count: 1848
[CONTINUOUS CHECK] Monitoring for post-count removal attempts...
Ready for next cycle

Cheat Detection:

[CHEATING DETECTED!] B→A removal sequence - Part being removed
SYSTEM STOPPING - Part already counted, cannot be removed!
[SYSTEM STOPPED] Machine halted due to cheating detection!
Session Count: 5
Lifetime Count: 1852
[EEPROM] Saved Machine Mode: REJECT

🚀 Getting Started

Setup Instructions

Hardware Assembly
- Connect ESP32 to PCF8574 modules via I2C (GPIO21=SDA, GPIO22=SCL)
- Connect buttons, sensors, and relays to appropriate PCF8574 pins
- Power up the system
Firmware Upload
- Open r_bin_interlock_sys.ino in Arduino IDE
- Select Board: ESP32 Dev Module
- Install ESP32 board package if not present
- Upload sketch to device
Initial Testing
- Open Serial Monitor (115200 baud)
- Verify EEPROM initialization (first boot will show "initializing EEPROM")
- Test AUTO button (should start machine)
- Test REJECT button (should stop machine)
- Test sensor sequences (A then B)
- Verify counts increment in EEPROM
Web Dashboard Access
- Connect to WiFi: RejectionBin_AP
- Navigate to: http://192.168.1.21
- View system status and session files

🔧 Configuration

Modifiable Parameters in `config.h`

#define MAX_START_FILES       100   // Keep last N boot sessions
#define POLL_INTERVAL         20    // Input polling frequency (ms)
#define I2C_RETRY_COUNT       3     // Retries per I2C transaction
#define I2C_FAILSAFE_THRESHOLD 5    // Consecutive failures before lock
#define BUTTON_DEBOUNCE_MS    120   // Min interval between valid button presses
#define BEEP_DURATION         500   // Beep length (ms)
#define FIRMWARE_VERSION      4     // Bump to reset EEPROM + SPIFFS on update

EEPROM Memory Map in `eeprom_operations.h`

#define EEPROM_SIZE           512     // Total EEPROM allocation
#define EEPROM_MAGIC          0xABCD  // First boot detection
#define ADDR_MAGIC            0       // Magic number address
#define ADDR_MACHINE_MODE     2       // Machine mode address
#define ADDR_LIFETIME_COUNT   3       // Lifetime count address
#define ADDR_BOOT_NUMBER      7       // Boot number address
#define ADDR_FW_VERSION      11       // Firmware version address

📝 System Features Summary

Feature	Details
Hybrid Storage	EEPROM for critical data + SPIFFS for history
Multi-Slot Detection	3 slots, each with dual sensors (A & B)
Anti-Cheat Monitoring	Continuous surveillance after A→B sequence
Boot Tracking	Counts power cycles and stores per-boot data
Lifetime Tracking	Never-reset total reject counter in EEPROM
Automatic Cleanup	Batch deletes old session files every 100 boots
Power-Loss Safe	EEPROM ensures data integrity
Fast Writes	3-4ms EEPROM writes (10x faster than SPIFFS)
Web Interface	WiFi AP mode with file browser and downloader
Serial Debugging	Full command interface for monitoring
LED/Buzzer Alerts	Visual and audio feedback for reject mode
Relay Control	Machine start/stop via digital relay output
I2C Expansion	8 inputs + 8 outputs via PCF8574 modules
I2C Fail-safe Lock	Forces REJECT mode after repeated I2C faults
Button Debounce	Filters bounce on AUTO/REJECT button edges
Non-blocking Serial	Prevents command input from stalling control loop

🐛 Troubleshooting

Issue	Solution
"EEPROM not initialized"	System will auto-initialize on first boot
"SPIFFS Mount failed"	Format SPIFFS from Arduino IDE Tools menu
Files not persisting	Check SPIFFS partition in board settings
EEPROM data corrupted	Magic number mismatch will trigger reset
I2C errors	Verify PCF8574 addresses (0x25, 0x26)
Counters reset unexpectedly	Check EEPROM initialization messages
Sensors not detecting	Verify PCF1 wiring and sensor power
Web dashboard not accessible	Check WiFi AP settings (SSID/Password)

📈 Performance Metrics

Metric	Value
Sensor poll rate	50 Hz (20ms interval)
Edge detection	Rising edge only
Button debounce	120 ms
Beep duration	500ms
EEPROM write time	3-4ms
SPIFFS write time	50-100ms
I2C retries/op	3
I2C fail-safe threshold	5 consecutive failures
I2C Speed	100 kHz
EEPROM write cycles	~100,000 per cell
Flash write cycles	~10,000 per block

🔒 Safety Features

✅ Machine interlock - Cannot start until rejected part confirmed
✅ State persistence - EEPROM ensures state survives power loss
✅ Dual-sensor confirmation - Prevents false positives
✅ Anti-cheat monitoring - Detects part removal attempts (B→A sequence)
✅ Visual/audio alerts - Operator awareness
✅ Data redundancy - EEPROM + SPIFFS backup
✅ Automatic cleanup - Prevents filesystem overflow
✅ Power-loss recovery - Atomic EEPROM writes
✅ Fast response - Critical writes complete in 3-4ms
✅ I2C fail-safe lock - Stops machine safely on repeated bus errors
✅ Button debounce filter - Reduces false trigger events

🗂️ Change Tracking

For a chronological list of firmware updates, see:

readme_updates.md

📄 License

👨‍💻 Development Notes

Code Organization: Modular header-based design for easy maintenance
Hybrid Storage: EEPROM for speed/reliability, SPIFFS for history
I2C Clock Speed: 100 kHz for stable communication
Edge Detection: Rising edge detection for button/sensor inputs
Non-blocking Beep: Beep timing managed in update_outputs() loop
EEPROM Magic Number: 0xABCD for first boot detection
Wear Leveling: EEPROM handles frequent writes better than flash

🔄 Migration from v2.0 to v3.0

If upgrading from SPIFFS-only version:

First boot will auto-migrate:
- EEPROM initializes with default values
- Existing SPIFFS files remain intact
- Boot number continues from last value
- Lifetime count may reset (one-time)
Manual migration (optional):
- Note your current boot_number and total_count
- Upload new firmware
- Use serial commands to verify EEPROM values
- Adjust if needed via code modification

⚠️ Disclaimer

This system is designed as a safety interlock and should not be the sole safety mechanism. Always follow proper industrial safety protocols and implement redundant safety systems for critical applications.

Name		Name	Last commit message	Last commit date
Latest commit History 44 Commits
.gitignore		.gitignore
config.h		config.h
eeprom_operations.h		eeprom_operations.h
file_operations.h		file_operations.h
io_operations.h		io_operations.h
process.h		process.h
r_bin_interlock_sys.ino		r_bin_interlock_sys.ino
readme.md		readme.md
readme_updates.md		readme_updates.md
reject.h		reject.h
serial_cmd.h		serial_cmd.h
web_server.h		web_server.h

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🏭 Rejection Bin Interlocking System

ESP32-Based Industrial Part Rejection control and Rejection count Logging system

📖 Overview

🆕 What's New in v4.0

🛡️ Runtime Hardening (Current Build)

🚀 Hybrid Storage Architecture (EEPROM + SPIFFS)

Why Hybrid Storage?

Storage Architecture

Automatic File Management

Example Timeline

📚 Libraries Used

🧰 Hardware Components

📂 Project Files Reference

Header Files (.h)

Main Program

🔌 Pin Mapping

ESP32 Hardware Pins

PCF8574 #1 (Address 0x25) - Input Expander

PCF8574 #2 (Address 0x26) - Output Expander

🛠️ Software Requirements

⚙️ System Operation Modes

AUTO Mode (Normal Production)

REJECT Mode (Waiting for Part Confirmation)

📊 Part Detection Sequence

Valid Rejection Workflow

Cheat Detection (Anti-Removal)

I2C Fail-safe Behavior

💾 Data Persistence Architecture

EEPROM Storage (Critical Data)

SPIFFS Storage (Session History)

Automatic File Management

Power Loss Recovery

Storage Capacity

🌐 Web Server & WiFi

WiFi AP Configuration

Web Dashboard Features

Web Dashboard Display

Important note

🖥️ Serial Command Interface

Serial Port Settings

Available Serial Commands

Serial Output During Operation

🚀 Getting Started

Setup Instructions

🔧 Configuration

Modifiable Parameters in config.h

EEPROM Memory Map in eeprom_operations.h

📝 System Features Summary

🐛 Troubleshooting

📈 Performance Metrics

🔒 Safety Features

🗂️ Change Tracking

📄 License

👨‍💻 Development Notes

🔄 Migration from v2.0 to v3.0

⚠️ Disclaimer

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Header Files (`.h`)

Modifiable Parameters in `config.h`

EEPROM Memory Map in `eeprom_operations.h`