Smart EV Charging Station with Battery Management System (BMS)

Arduino Nano • GSM SIM900A • Battery Safety Monitoring • Smart Charging Control

Selected and presented at State-Level Technical Exhibition

Physical prototype: Arduino Nano (center-left) • GSM SIM900A (blue board, bottom) • 16×2 LCD display (active) • 3S BMS module (bottom-right, XT60 connector) • SSR charging control • LM35 temperature sensor — fully wired on perfboard and demonstrated live at state-level exhibition.

Project Overview
Problem Statement
System Architecture
Features
Working Flow
Hardware Components
- Hardware Prototype
Technical Specifications
GSM Communication Flow
Battery Safety Logic
Charging State Machine
Key Engineering Contributions
Results
Applications
Future Engineering Enhancements
Folder Structure
Documentation
License

Project Overview

The Smart EV Charging Station with BMS is an embedded systems project that automates electric vehicle charging at the station level using an Arduino Nano microcontroller. The system integrates GSM SIM900A for SMS-based UPI payment verification, a commercial BMS module for multi-layer battery protection, a Solid State Relay (SSR) for silent charging control, and an LM35 temperature sensor for thermal safety monitoring.

The project was physically built and demonstrated — not a simulation. It was selected for a State-Level Technical Exhibition, validating the engineering approach and practical implementation.

Academic Scope: This is a diploma-level prototype. Commercial deployment would require grid certification, safety approvals, and industrial-grade hardware beyond this project's scope.

Problem Statement

India's EV adoption is accelerating — 30% CAGR in EV sales — but charging infrastructure is critically underdeveloped:

Unmanaged charging degrades battery packs prematurely, costing EV owners ₹30,000–₹80,000 in early replacements
No payment intelligence at small stations forces cash-only or manual billing, creating fraud and reconciliation problems
Thermal runaway incidents in Li-ion batteries are rising due to overcharging without temperature monitoring
Over-voltage conditions on 3S–4S packs go undetected in low-cost chargers, permanently damaging cells
Existing solutions (commercial EVSE) cost ₹1.5L–₹5L per point — unaffordable for college campuses, apartment parking, or rural setups

This project addresses all five problems in a sub-₹3,000 hardware budget, demonstrating that smart EV charging is achievable at a low cost.

System Architecture

graph TD
    A[EV User] -->|Sends UPI Payment SMS| B[GSM SIM900A Module]
    B -->|AT Commands + Serial| C[Arduino Nano ATmega328P]

    C --> D[BMS Module]
    D --> D1[Overvoltage Protection]
    D --> D2[Overcurrent Protection]
    D --> D3[Short Circuit Protection]
    D --> D4[Cell Balancing]

    C --> E[LM35 Temperature Sensor]
    E -->|Analog Voltage → ADC| C

    C --> F[Voltage Divider Circuit]
    F -->|Scaled Battery Voltage → ADC| C

    C --> G[Solid State Relay SSR]
    G -->|Controls Charging Circuit| H[EV Battery Pack]

    C --> I[LCD 16x2 Display]
    I --> I1[SOC %]
    I --> I2[Voltage V]
    I --> I3[Temperature °C]
    I --> I4[Status Message]

    H --> D
    D --> F

    style A fill:#4CAF50,color:#fff
    style C fill:#2196F3,color:#fff
    style D fill:#9C27B0,color:#fff
    style G fill:#FF5722,color:#fff
    style B fill:#FF9800,color:#fff

Block Diagram

graph LR
    subgraph INPUT ["INPUT LAYER"]
        GSM[GSM SIM900A\nUPI SMS]
        TEMP[LM35\nTemperature]
        VOLT[Voltage Divider\nBattery Voltage]
    end

    subgraph CONTROLLER ["CONTROLLER - Arduino Nano"]
        MCU[ATmega328P\n32KB Flash / 2KB SRAM]
    end

    subgraph PROTECTION ["PROTECTION LAYER"]
        BMS[BMS Module\nMulti-Protection IC]
    end

    subgraph OUTPUT ["OUTPUT LAYER"]
        SSR[Solid State Relay\nCharging Control]
        LCD[16×2 LCD\nUser Display]
    end

    GSM --> MCU
    TEMP --> MCU
    VOLT --> MCU
    MCU --> BMS
    MCU --> SSR
    MCU --> LCD
    BMS --> SSR

Features

Feature	Description	Status
GSM-Enabled Charging	SIM900A receives and parses UPI payment SMS to authorize charging	✅ Implemented
UPI Payment Verification	Parses incoming SMS for payment confirmation before releasing charge	✅ Implemented
Smart Charging Duration	Calculates charging time based on detected battery level and unit rate	✅ Implemented
Battery Voltage Monitoring	Voltage divider + Arduino ADC reads pack voltage every 2 seconds	✅ Implemented
Temperature Protection	LM35 monitors cell temperature; SSR cuts off above threshold	✅ Implemented
Over-Voltage Protection	BMS module triggers hardware cutoff at configurable voltage limit	✅ Implemented
Battery Health Management	BMS enforces charge/discharge limits to preserve long-term capacity	✅ Implemented
LCD Feedback System	16×2 LCD shows SOC %, voltage, temperature, and session status in real-time	✅ Implemented
SSR Charging Control	Silent solid-state switching — no mechanical wear, zero arcing	✅ Implemented
Session Logging	Stores charging session timestamps and energy data in EEPROM	✅ Implemented
Fault Detection	Software detects GSM failure, over-temperature, and voltage fault states	✅ Implemented
Auto Reset	System returns to IDLE after fault clearance or session completion	✅ Implemented

Working Flow

flowchart TD
    START([System Power ON]) --> INIT[Initialize\nLCD, GSM, ADC, BMS]
    INIT --> IDLE[IDLE STATE\nLCD: Awaiting Payment]

    IDLE --> GSM_POLL{Poll GSM\nfor SMS}
    GSM_POLL -->|No SMS| IDLE
    GSM_POLL -->|SMS received| PARSE[Parse SMS\nVerify UPI Keywords]

    PARSE -->|Invalid / Unknown| REJECT[Reject - Log Event\nLCD: Invalid Payment]
    REJECT --> IDLE

    PARSE -->|Valid UPI Confirmation| PRE_CHECK[Pre-Charge Safety Check]

    PRE_CHECK --> VOLT_CHECK{Battery Voltage\nwithin safe range?}
    VOLT_CHECK -->|No - Overvoltage| FAULT_OV[FAULT: Overvoltage\nSSR OFF, LCD Alert]
    VOLT_CHECK -->|Yes| TEMP_CHECK{Temperature\n< Threshold?}

    TEMP_CHECK -->|No - Overtemp| FAULT_OT[FAULT: Overtemperature\nSSR OFF, LCD Alert]
    TEMP_CHECK -->|Yes| START_CHARGE[START CHARGING\nSSR ON\nLCD: Charging...]

    START_CHARGE --> MONITOR_LOOP{Real-Time Monitor\nEvery 2 seconds}

    MONITOR_LOOP --> VOLT_MON{Voltage OK?}
    VOLT_MON -->|No| FAULT_OV
    VOLT_MON -->|Yes| TEMP_MON{Temperature OK?}

    TEMP_MON -->|No| FAULT_OT
    TEMP_MON -->|Yes| SOC_CHECK{SOC ≥ 100%?}

    SOC_CHECK -->|No| TIME_CHECK{Session time\nexceeded?}
    TIME_CHECK -->|No| UPDATE_LCD[Update LCD\nSOC / Temp / Voltage]
    UPDATE_LCD --> MONITOR_LOOP

    TIME_CHECK -->|Yes| SESSION_END
    SOC_CHECK -->|Yes| SESSION_END

    SESSION_END[END SESSION\nSSR OFF\nLog to EEPROM] --> BILL_DISPLAY[LCD: Session Summary\nEnergy + Duration]
    BILL_DISPLAY --> IDLE

    FAULT_OV --> FAULT_CLEAR{Fault Cleared?}
    FAULT_OT --> FAULT_CLEAR
    FAULT_CLEAR -->|Yes| IDLE
    FAULT_CLEAR -->|No| FAULT_OV

    style START fill:#4CAF50,color:#fff
    style START_CHARGE fill:#2196F3,color:#fff
    style SESSION_END fill:#4CAF50,color:#fff
    style FAULT_OV fill:#f44336,color:#fff
    style FAULT_OT fill:#f44336,color:#fff
    style IDLE fill:#607D8B,color:#fff

Hardware Components

Hardware Prototype

Physical prototype assembled on perfboard and demonstrated at State-Level Technical Exhibition. All major components are visible: Arduino Nano (main controller), GSM SIM900A (blue board with SIM slot), 16×2 LCD display (showing live readings), 3S BMS protection module (bottom-right, XT60 battery connector), Schneider MCB circuit breaker (top-right, safety isolation), LM35 temperature sensor, and the SSR-controlled charging circuit. The Jio SIM-based power adapter (top-left) powers the 2G network modem during live demonstration.

Component List

Component	Specification	Quantity	Purpose
Arduino Nano	ATmega328P, 32KB Flash, 2KB SRAM, 16MHz	1	Main controller
GSM SIM900A	Quad-band 850/900/1800/1900 MHz, UART	1	SMS-based payment verification
BMS Module	3S / 4S Li-ion protection, 10A rated	1	Battery protection (overcurrent, overvoltage, short circuit)
Solid State Relay (SSR)	5V control, 24V/10A output	1	Silent charging circuit switching
LM35 Temperature Sensor	10mV/°C, −55°C to +150°C, ±0.5°C accuracy	1	Cell temperature monitoring
LCD 16×2	HD44780 compatible, 5V	1	User status display
Voltage Divider	R1=10kΩ, R2=4.7kΩ for pack voltage scaling	1 set	Battery voltage sensing
SIM Card Slot	Any 2G-capable SIM (Jio/Airtel/BSNL)	1	GSM connectivity
Lithium Battery Pack	3S 18650 (11.1V nominal)	1	Simulated EV battery
Breadboard / PCB	830-point breadboard or custom PCB	1	Circuit assembly
Power Supply	12V 2A adapter + 7805 regulator for 5V rail	1	System power
10kΩ Resistors	Pull-up / voltage divider	4	Signal conditioning
4.7kΩ Resistors	Voltage divider lower leg	2	Voltage scaling
Decoupling Caps	100nF ceramic, 10µF electrolytic	4	Power supply filtering

Arduino Nano Pin Mapping

Arduino Nano Pin	Connected To	Type
D0 (RX)	USB / Serial monitor	Hardware UART RX (debug only)
D1 (TX)	USB / Serial monitor	Hardware UART TX (debug only)
D2	LCD RS	Digital OUT
D3	LCD Enable	Digital OUT
D4–D7	LCD D4–D7	Digital OUT
D8	SSR Control Signal	Digital OUT
D9	Status LED (Green)	Digital OUT
D10	Alert LED (Red)	Digital OUT
D11	Buzzer	Digital OUT
D12	GSM SIM900A TX	SoftwareSerial RX
D13	GSM SIM900A RX	SoftwareSerial TX
A0	LM35 Output	Analog IN (ADC)
A1	Voltage Divider Output	Analog IN (ADC)
5V / GND	All module VCC/GND	Power

Technical Specifications

Parameter	Value
Microcontroller	ATmega328P @ 16 MHz
Flash / SRAM	32 KB / 2 KB
GSM Module	SIM900A (Quad-band 2G)
GSM Interface	SoftwareSerial @ 9600 baud
Voltage Sensing Range	9.0V – 12.6V (3S Li-ion operating range; ADC limit ≈ 15.6V)
ADC Resolution	10-bit (1024 steps, 4.88mV/step)
Voltage Divider Ratio	0.32× (R1=10kΩ, R2=4.7kΩ)
Temperature Range	0°C – 85°C (LM35 operating range used)
Temperature Cutoff	45°C (software configurable)
Overvoltage Cutoff	4.20V/cell (BMS module hardware limit)
SSR Control Logic	5V HIGH = relay ON (active HIGH)
Sensor Poll Interval	2000 ms
LCD Update Interval	2000 ms
EEPROM Session Records	Up to 90 sessions (ring buffer, 11 bytes/record in 1KB EEPROM)
Battery Chemistry	Li-ion 18650 (3S configuration)
Nominal Pack Voltage	11.1V (3S)
Charging Cutoff Voltage	12.6V (4.2V × 3 cells)
System Power	5V from 7805 regulator
GSM SIM900A Power	4V / 2A (separate supply required)

GSM Communication Flow

sequenceDiagram
    participant User as EV User
    participant Phone as User's Phone
    participant GSM as GSM SIM900A
    participant MCU as Arduino Nano
    participant SSR as Solid State Relay
    participant LCD as 16×2 LCD

    User->>Phone: Sends UPI Payment\nto Station Number
    Phone->>GSM: SMS Delivery\n"Payment of Rs 50 successful"
    GSM->>MCU: AT+CMGL="ALL"\nReturns raw SMS text
    MCU->>MCU: Parse SMS\nSearch for payment keywords
    MCU->>LCD: "Payment Received\nVerifying..."

    alt Valid UPI Confirmation
        MCU->>MCU: Extract amount\nCalculate charge duration
        MCU->>SSR: Set HIGH (Relay ON)
        MCU->>LCD: "Charging Started\nSOC: XX%"
        MCU->>GSM: AT+CMGS\nSend reply SMS to user
        GSM->>Phone: "Charging started.\nStation EV-01"

        loop Every 2 seconds
            MCU->>MCU: Read ADC (Voltage + Temp)
            MCU->>LCD: Update SOC / Temp / Time
        end

        MCU->>SSR: Set LOW (Relay OFF)
        MCU->>LCD: "Session Complete\nEnergy: X.X Wh"
        MCU->>GSM: AT+CMGS\nSend completion SMS
        GSM->>Phone: "Charging complete.\nDuration: XX min"

    else Invalid / Unknown SMS
        MCU->>LCD: "Invalid Payment\nRetry or Contact"
        MCU->>GSM: AT+CMGD\nDelete invalid SMS
    end

Battery Safety Logic

flowchart TD
    READ[Read Sensors\nVoltage + Temperature] --> V_CHECK{Voltage >\n4.20V/cell?}

    V_CHECK -->|YES| OV_FAULT[OVERVOLTAGE FAULT\nBMS Hardware Cutoff\nSSR OFF\nLCD: OV FAULT]

    V_CHECK -->|NO| T_CHECK{Temperature >\n45°C?}

    T_CHECK -->|YES| OT_FAULT[OVERTEMP FAULT\nSSR OFF immediately\nLCD: TEMP FAULT\nBuzzer Alert]

    T_CHECK -->|NO| SAFE[All SW Checks Pass\nContinue Charging]

    SAFE --> SOC_EST[Estimate SOC\nfrom Voltage Curve]
    SOC_EST --> FULL_CHECK{SOC >= 98%?}

    FULL_CHECK -->|YES| CHARGE_DONE[Charging Complete\nSSR OFF\nLog Session]
    FULL_CHECK -->|NO| READ

    OV_FAULT --> WAIT{Voltage drops\nbelow threshold?}
    OT_FAULT --> WAIT2{Temperature\ncools down?}
    WAIT -->|YES| READ
    WAIT2 -->|YES| READ

    BMS_HW[BMS Hardware Module\nIndependent Overcurrent\nand Short-Circuit Protection]

    style OV_FAULT fill:#f44336,color:#fff
    style OT_FAULT fill:#f44336,color:#fff
    style SAFE fill:#4CAF50,color:#fff
    style CHARGE_DONE fill:#2196F3,color:#fff
    style BMS_HW fill:#9C27B0,color:#fff

Charging State Machine

stateDiagram-v2
    [*] --> IDLE : System Power ON

    IDLE --> PAYMENT_PENDING : GSM SMS Received
    PAYMENT_PENDING --> IDLE : Payment Invalid
    PAYMENT_PENDING --> PRE_CHECK : Payment Valid

    PRE_CHECK --> CHARGING : All Safety Checks Pass
    PRE_CHECK --> FAULT : Safety Check Failed

    CHARGING --> MONITORING : SSR ON, Sensors Active
    MONITORING --> CHARGING : Parameters Normal
    MONITORING --> FAULT : Overvoltage / Overtemp / BMS Trip
    MONITORING --> SESSION_END : SOC = 100% or Time Elapsed

    SESSION_END --> IDLE : Session Logged, LCD Summary Shown

    FAULT --> FAULT_DISPLAY : Show Fault on LCD + Buzzer
    FAULT_DISPLAY --> IDLE : Fault Cleared (Auto/Manual)

Key Engineering Contributions

Designed and implemented a multi-layer battery protection system combining hardware BMS module cutoffs with software-level voltage and temperature monitoring on an Arduino Nano
Developed an SMS-parsing algorithm in C++ (within 32KB flash constraint) to verify UPI payment confirmations received via GSM SIM900A AT commands
Engineered a time-based smart charging algorithm that dynamically calculates session duration from real-time battery voltage measurements
Integrated LM35 analog temperature sensing with ADC reading, converting raw ADC counts to Celsius with software calibration
Implemented a voltage divider circuit and ADC-based pack voltage sensing pipeline with a software scaling factor for accurate 3S Li-ion voltage display
Built a complete SSR control logic ensuring silent, arc-free charging circuit switching with proper state machine transitions
Programmed 16×2 LCD feedback system with real-time SOC estimation display, temperature, and session status messages
Delivered a working physical prototype within Arduino Nano's 32KB flash and 2KB SRAM resource constraints
Presented the complete system at a State-Level Technical Exhibition, demonstrating live charging sessions with GSM payment integration

Results

Test	Observation
Payment SMS parsing	GSM SIM900A successfully parsed incoming SMS and triggered charging relay within ~3 seconds of SMS delivery
Temperature protection	Software cutoff triggered correctly when LM35 reading exceeded configured threshold during thermal test
Voltage monitoring	ADC-based voltage reading accurate within ±0.1V across 3S pack voltage range (9.0V–12.6V)
SSR switching	Solid state relay operated silently on every state transition; no mechanical wear observed
LCD display	Real-time SOC and temperature updates displayed at 2-second intervals throughout charging session
BMS protection	Commercial BMS module correctly prevented overcharging beyond 4.20V/cell during extended test
EEPROM logging	Session timestamps and energy data persisted across power cycles
State exhibition	System demonstrated live to judges at state-level event; selected for presentation

Applications

Smart EV charging stations — campus, residential, and small commercial setups
Fleet vehicle charging — autorickshaw and two-wheeler fleet depots
Campus charging systems — engineering colleges, hospitals, corporate offices
Residential charging — apartment-level EV charging with payment metering
Smart parking solutions — integrated charging + parking payment kiosks
Rural EV infrastructure — low-cost GSM-connected charging where Wi-Fi is unavailable

Future Engineering Enhancements

These are proposed upgrades only — not implemented in the current prototype. Listed to demonstrate awareness of production-grade engineering requirements.

Version	Enhancement	Technology	Benefit
V2	Replace Arduino Nano with ESP32	ESP32 DevKit	Wi-Fi, BLE, faster processing, more flash
V2	RFID / QR Authentication	MFRC522 / QR Scanner	User-specific session tracking
V3	MQTT IoT Dashboard	ESP32 + Mosquitto + Flask	Real-time remote monitoring
V3	Cloud Connectivity	AWS IoT Core / Firebase	Multi-station management
V4	Mobile Application	Flutter (Android + iOS)	User-facing app with session history
V4	UPI SDK Integration	Razorpay / PhonePe API	Verified cashless payment (not SMS-based)
V5	AI Battery Degradation Prediction	LSTM / TensorFlow Lite	Predict remaining battery life
V5	Adaptive Charging Algorithm	ML on sensor data	Optimize charge rate for battery health
V6	OCPP 1.6 Protocol	Open Charge Point Protocol	Interoperability with commercial CSMS
V6	Smart Grid Integration	Grid signal API	Demand-response charging
V6	Solar MPPT Integration	MPPT controller	Solar-assisted off-grid charging

See docs/version_2_roadmap.md for detailed roadmap.

Folder Structure

SmartEV-Charging-System/
│
├── README.md                          # This file
├── AUDIT_REPORT.md                    # Project audit and findings
├── LICENSE                            # MIT License
├── CONTRIBUTING.md                    # Contribution guidelines
├── CODE_OF_CONDUCT.md                 # Code of conduct
│
├── docs/
│   ├── architecture.md                # System architecture deep-dive
│   ├── working-principle.md           # How the system works
│   ├── hardware-requirements.md       # BOM, circuit, pin mapping
│   ├── BMS_Design.md                  # Battery management documentation
│   ├── GSM_Integration.md             # GSM AT commands and payment flow
│   ├── future-improvements.md         # Detailed future scope
│   ├── version_2_roadmap.md           # V2–V6 engineering roadmap
│   ├── demo_storyboard.md             # Demo GIF storyboard
│   └── banner_concept.md              # Repository banner design concept
│
├── firmware/
│   └── arduino/
│       └── smart_ev_charger/
│           ├── smart_ev_charger.ino   # Main Arduino sketch (state machine)
│           ├── config.h               # Pin definitions, thresholds, EEPROM layout
│           ├── bms.h / bms.cpp        # Voltage + temp sensing, SOC estimation
│           └── gsm.h / gsm.cpp        # SIM900A driver + UPI SMS parser
│
├── images/
│   ├── README.md                      # Image descriptions
│   └── diagrams/                      # Mermaid diagram exports (PNG/SVG)
│
├── presentations/
│   └── exhibition_slides_concept.md   # State-level exhibition slide concepts
│
└── LINKEDIN_POST.md                   # LinkedIn showcase post
    PROJECT_SUMMARY_FOR_RESUME.md      # Resume bullet points

Documentation

Document	Description
Architecture	System architecture, communication flows, design decisions
Working Principle	Step-by-step operational flow
Hardware Requirements	BOM, circuit description, pin mapping
BMS Design	Battery protection logic, SOC estimation, safety thresholds
GSM Integration	AT command sequences, SMS parsing, payment verification
Future Improvements	Detailed future scope analysis
Version 2 Roadmap	V2–V6 engineering progression plan
Audit Report	Full project audit and engineering assessment

License

This project is licensed under the MIT License.

Built as a Diploma Final Year Project — physically demonstrated at State-Level Technical Exhibition.
Not certified for commercial or grid-connected deployment.

Arduino Nano • GSM SIM900A • BMS • SSR • LM35 • LCD

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Smart EV Charging Station with Battery Management System (BMS)

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Project Overview

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Hardware Prototype

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assets		assets
docs		docs
firmware		firmware
hardware		hardware
images		images
presentations		presentations
simulation		simulation
software		software
tests		tests
.env.example		.env.example
.gitignore		.gitignore
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CODE_OF_CONDUCT.md		CODE_OF_CONDUCT.md
CONTRIBUTING.md		CONTRIBUTING.md
LICENSE		LICENSE
LINKEDIN_POST.md		LINKEDIN_POST.md
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README.md		README.md

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Smart EV Charging Station with Battery Management System (BMS)

Table of Contents

Project Overview

Problem Statement

System Architecture

Block Diagram

Features

Working Flow

Hardware Components

Hardware Prototype

Component List

Arduino Nano Pin Mapping

Technical Specifications

GSM Communication Flow

Battery Safety Logic

Charging State Machine

Key Engineering Contributions

Results

Applications

Future Engineering Enhancements

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