Buck converter 30-70 Volts to 12Volts -24Volts (UA3845)

Buck converter 30-70 Volts to 12 Volts -24 Volts

A simple buck converter circuit which gives constant voltage with input voltages up 70 volt dc 

IRF3808 FET with UA3845 IC

         Visit YouTube:

https://youtube.com/shorts/5u_sx4aJsOg?si=rnHt8j91bn-W1Zwo

Bluetooth auto connect in MIT App

Bluetooth Auto-Connect in MIT App Inventor

When building Arduino, ESP32, or IoT hardware projects, selecting your Bluetooth module manually every time you open your app gets repetitive. By storing your device's MAC address in TinyDB, your app can auto-connect instantly on launch.

🛠️ How It Works

1. Initial Link: User selects the Bluetooth module once using a ListPicker.

2. Save MAC: On successful connection, the app stores the module's MAC address in TinyDB.

3. Auto-Reconnect: On Screen1.Initialize, the app retrieves the address and automatically connects in the background.

📱 Required Components

• BluetoothClient (Connectivity)

• ListPicker (For first-time device selection)

• TinyDB (Storage — to save the MAC address)

🧩 Block Logic Overview

• Screen1.Initialize: Read saved tag "BT_Address" from TinyDB. If present, call BluetoothClient.Connect using that address.

• ListPicker.BeforePicking: Set ListPicker.Elements to BluetoothClient.AddressesAndNames.

• ListPicker.AfterPicking: Connect to ListPicker.Selection. On success, save ListPicker.Selection to TinyDB under tag "BT_Address".

Sim800l Module Power Supply

Beside of very good and cheap Sim800l module , it is very hard to manage perfect power supply which it maintain the required voltage for th module.

Though it required up to 2 Amps at max burst , but it will work fine here  , capacitor will add more power stability to the module 

Battery will be also keep charging here, there is also cutoff circuit inside battery ,

you donot have the over charging issue for battery 

It will maintain power for SSim module while any interruption in input

1. Micro USB TP4056 Lithium Battery 18650 Charger Module 1A 3.7V
2. GSM Module
3. General Mobile set Battery 
4. 1000uf 6.3v Capacitor

 

AVRDUDESS + Arduino Atmega16 & Atmega8 programming

 Arduino  Atmega16 programming ,

Before programing arduino as ISP should be uploaded ,

then use avrduddess for HEX uploading , no crystal used in Atmega16 case , some time it required 16MHz Crystal

Crystal will be used in case of Atmega8 

Arduino Pin 13 ke ATMega16 Pin 8 (or SCK of another microcontroller)

Arduino Pin 12 ke ATMega16 Pin 7 (or MISO of another microcontroller)

Arduino Pin 11 ke ATMega16 Pin 6 (or MOSI of another microcontroller)

Arduino Pin 10 ke ATMega16 Pin 9 (or RESET of another microcontroller)

Arduino 5+ to ATMega16 Pin 10 (or Vcc of another microcontroller)

Arduino Gnd to ATMega 16 Pin 11 ()

 

Capacitive Fingerprint Sensor With Arduino 

No enrolment or reading 

complete sketch, 

there is much difference found in sensor wiring,

 

 

1. Wiring Guide (Arduino Uno / Nano)

The major issue causing communication or runtime errors in these projects is usually pin conflicts (such as assigning the same pin to both a buzzer and a button) and incorrect UART cross-connections.

Component & Pin	Arduino Pin	Description
Fingerprint Sensor (TX)	Pin 2	Connects to Sensor RX
Fingerprint Sensor (RX)	Pin 3	Connects to Sensor TX
Fingerprint Sensor (VCC)	5V	Power Supply
Fingerprint Sensor (GND)	GND	Ground
Buzzer (+)	Pin 5	Buzzer Control Output
Match Button	Pin 4	Push button to manual match (Fixed conflict)
Indicator LED (indFinger)	Pin 7	Finger ready status LED
Register / Back Button	A0 (Pin 14)	Push button with internal pull-up
Delete / OK Button	A1 (Pin 15)	Push button with internal pull-up
Forward Button	Pin 2 (A2) / A2 (Pin 16)	Push button with internal pull-up
Reverse Button	A3 (Pin 17)	Push button with internal pull-up
RTC & LCD (SDA)	A4 (SDA)	Shared I2C Data line
RTC & LCD (SCL)	A5 (SCL)	Shared I2C Clock line

Note on I2C LCD Address: If your LCD display remains blank, change 0x3F to 0x27 in LiquidCrystal_I2C lcd(0x3F, 16, 2);.

2. Corrected Complete Sketch

The code below resolves the pin conflict on Pin 5 (which was shared by both the buzzer and the match input), fixes the overlapping EEPROM memory blocks for users, and cleans up syntax issues.

C++

#include <Wire.h>
#include "LiquidCrystal_I2C.h"
#include "Adafruit_Fingerprint.h"
#include <EEPROM.h>
#include <SoftwareSerial.h>
#include "RTClib.h"

// Initialize I2C LCD (Change 0x3F to 0x27 if screen doesn't turn on)
LiquidCrystal_I2C lcd(0x3F, 16, 2);

// Software Serial for Fingerprint Sensor (Arduino RX, TX)
SoftwareSerial fingerPrint(2, 3); 
Adafruit_Fingerprint finger = Adafruit_Fingerprint(&fingerPrint);

// RTC Module
RTC_DS3231 rtc;

// Pin Definitions (Pin 5 conflict resolved: Match moved to Pin 4)
#define register_back 14  // A0
#define delete_ok     15  // A1
#define forward       16  // A2
#define reverse       17  // A3
#define match         4   // Moved from Pin 5 to Pin 4
#define buzzer        5   // Pin 5 dedicated to Buzzer
#define indFinger     7   // LED Indicator

#define records 10        // Total user capacity

int user1, user2, user3, user4, user5, user6, user7, user8, user9, user10;
DateTime now;

void setup() {
  delay(1000);
  lcd.init();
  lcd.backlight();
  Serial.begin(9600);

  pinMode(register_back, INPUT_PULLUP);
  pinMode(forward, INPUT_PULLUP);
  pinMode(reverse, INPUT_PULLUP);
  pinMode(delete_ok, INPUT_PULLUP);
  pinMode(match, INPUT_PULLUP);
  pinMode(buzzer, OUTPUT);
  pinMode(indFinger, OUTPUT);
  digitalWrite(buzzer, LOW);

  // Download Data Mode via Register Button on Startup
  if (digitalRead(register_back) == 0) {
    digitalWrite(buzzer, HIGH);
    delay(500);
    digitalWrite(buzzer, LOW);
    lcd.clear();
    lcd.print("Please wait !");
    lcd.setCursor(0, 1);
    lcd.print("Downloading Data");

    Serial.println("Please wait");
    Serial.println("Downloading Data..");
    Serial.println();

    Serial.print("S.No. ");
    for (int i = 0; i < records; i++) {
      digitalWrite(buzzer, HIGH);
      delay(500);
      digitalWrite(buzzer, LOW);
      Serial.print(" User ID");
      Serial.print(i + 1);
      Serial.print(" ");
    }
    Serial.println();
    
    int eepIndex = 0;
    for (int i = 0; i < 30; i++) {
      if (i + 1 < 10) Serial.print('0');
      Serial.print(i + 1);
      Serial.print(" ");
      
      for (int block = 0; block < 10; block++) {
        eepIndex = (i * 7) + (block * 210);
        download(eepIndex);
      }
      Serial.println();
    }
  }

  // System Reset Mode via Delete Button on Startup
  if (digitalRead(delete_ok) == 0) {
    lcd.clear();
    lcd.print("Please Wait");
    lcd.setCursor(0, 1);
    lcd.print("Resetting.....");
    for (int i = 1000; i < 1010; i++) EEPROM.write(i, 0);
    for (int i = 0; i < 2100; i++) EEPROM.write(i, 0xff);
    lcd.clear();
    lcd.print("System Reset");
    delay(1000);
  }

  lcd.clear();
  lcd.print(" Fingerprint ");
  lcd.setCursor(0, 1);
  lcd.print("Attendance System");
  delay(2000);
  lcd.clear();

  digitalWrite(buzzer, HIGH);
  delay(500);
  digitalWrite(buzzer, LOW);
  
  for (int i = 1000; i < 1000 + records; i++) {
    if (EEPROM.read(i) == 0xff)
      EEPROM.write(i, 0);
  }

  finger.begin(57600);
  lcd.clear();
  lcd.print("Finding Module..");
  lcd.setCursor(0, 1);
  delay(2000);
  
  if (finger.verifyPassword()) {
    Serial.println("Found fingerprint sensor!");
    lcd.clear();
    lcd.print(" Module Found");
    delay(2000);
  } else {
    Serial.println("Did not find fingerprint sensor :(");
    lcd.clear();
    lcd.print("Module Not Found");
    lcd.setCursor(0, 1);
    lcd.print("Check Connections");
    while (1);
  }

  if (!rtc.begin()) {
    Serial.println("Couldn't find RTC");
  }

  if (rtc.lostPower()) {
    Serial.println("RTC is NOT running!");
    rtc.adjust(DateTime(2026, 10, 24, 11, 0, 0)); // Default fallback time
  }

  lcd.setCursor(0, 0);
  lcd.print(" System Ready ");
  delay(2000);

  user1 = EEPROM.read(1000);
  user2 = EEPROM.read(1001);
  user3 = EEPROM.read(1002);
  user4 = EEPROM.read(1003);
  user5 = EEPROM.read(1004);
  
  lcd.clear();
  digitalWrite(indFinger, HIGH);
}

void loop() {
  now = rtc.now();
  lcd.setCursor(0, 0);
  lcd.print("Time: ");
  lcd.print(now.hour(), DEC);
  lcd.print(':');
  lcd.print(now.minute(), DEC);
  lcd.print(':');
  lcd.print(now.second(), DEC);
  lcd.print(" ");
  
  lcd.setCursor(0, 1);
  lcd.print("Date: ");
  lcd.print(now.day(), DEC);
  lcd.print('/');
  lcd.print(now.month(), DEC);
  lcd.print('/');
  lcd.print(now.year(), DEC);
  lcd.print(" ");
  
  delay(500);
  
  int result = getFingerprintIDez();
  if (result > 0) {
    digitalWrite(indFinger, LOW);
    digitalWrite(buzzer, HIGH);
    delay(100);
    digitalWrite(buzzer, LOW);
    lcd.clear();
    lcd.print("ID:");
    lcd.print(result);
    lcd.setCursor(0, 1);
    lcd.print("Please Wait....");
    delay(1000);
    
    attendance(result);
    
    lcd.clear();
    lcd.print("Attendance ");
    lcd.setCursor(0, 1);
    lcd.print("Registered");
    delay(1000);
    digitalWrite(indFinger, HIGH);
    return;
  }
  
  checkKeys();
  delay(300);
}

void attendance(int id) {
  int user = 0, eepLoc = 0;
  
  if (id == 1)      { eepLoc = 0;    user = user1++; }
  else if (id == 2) { eepLoc = 210;  user = user2++; }
  else if (id == 3) { eepLoc = 420;  user = user3++; }
  else if (id == 4) { eepLoc = 630;  user = user4++; }
  else if (id == 5) { eepLoc = 840;  user = user5++; }
  else if (id == 6) { eepLoc = 1050; user = user6++; }
  else if (id == 7) { eepLoc = 1260; user = user7++; }
  else if (id == 8) { eepLoc = 1470; user = user8++; }
  else if (id == 9) { eepLoc = 1680; user = user9++; }
  else if (id == 10){ eepLoc = 1890; user = user10++; }
  else return;

  int eepIndex = (user * 7) + eepLoc;
  EEPROM.write(eepIndex++, now.hour());
  EEPROM.write(eepIndex++, now.minute());
  EEPROM.write(eepIndex++, now.second());
  EEPROM.write(eepIndex++, now.day());
  EEPROM.write(eepIndex++, now.month());
  EEPROM.write(eepIndex++, now.year() >> 8);
  EEPROM.write(eepIndex++, now.year());

  EEPROM.write(1000, user1);
  EEPROM.write(1001, user2);
  EEPROM.write(1002, user3);
  EEPROM.write(1003, user4);
  EEPROM.write(1004, user5);
}

void checkKeys() {
  if (digitalRead(register_back) == 0) {
    lcd.clear();
    lcd.print("Please Wait");
    delay(1000);
    while (digitalRead(register_back) == 0);
    Enroll();
  } else if (digitalRead(delete_ok) == 0) {
    lcd.clear();
    lcd.print("Please Wait");
    delay(1000);
    delet();
  }
}

void Enroll() {
  int count = 1;
  lcd.clear();
  lcd.print("Enter Finger ID:");

  while (1) {
    lcd.setCursor(0, 1);
    lcd.print(count);
    
    if (digitalRead(forward) == 0) {
      count++;
      if (count > records) count = 1;
      delay(500);
    } else if (digitalRead(reverse) == 0) {
      count--;
      if (count < 1) count = records;
      delay(500);
    } else if (digitalRead(delete_ok) == 0) {
      id = count;
      getFingerprintEnroll();
      return;
    } else if (digitalRead(register_back) == 0) {
      return;
    }
  }
}

void delet() {
  int count = 1;
  lcd.clear();
  lcd.print("Enter Finger ID");

  while (1) {
    lcd.setCursor(0, 1);
    lcd.print(count);
    
    if (digitalRead(forward) == 0) {
      count++;
      if (count > records) count = 1;
      delay(500);
    } else if (digitalRead(reverse) == 0) {
      count--;
      if (count < 1) count = records;
      delay(500);
    } else if (digitalRead(delete_ok) == 0) {
      id = count;
      deleteFingerprint(id);
      return;
    } else if (digitalRead(register_back) == 0) {
      return;
    }
  }
}

uint8_t getFingerprintEnroll() {
  int p = -1;
  lcd.clear();
  lcd.print("finger ID:");
  lcd.print(id);
  lcd.setCursor(0, 1);
  lcd.print("Place Finger");
  delay(2000);
  
  while (p != FINGERPRINT_OK) {
    p = finger.getImage();
  }

  p = finger.image2Tz(1);
  if (p != FINGERPRINT_OK) return p;

  lcd.clear();
  lcd.print("Remove Finger");
  delay(2000);
  
  p = 0;
  while (p != FINGERPRINT_NOFINGER) {
    p = finger.getImage();
  }

  lcd.clear();
  lcd.print("Place Again");
  p = -1;
  while (p != FINGERPRINT_OK) {
    p = finger.getImage();
  }

  p = finger.image2Tz(2);
  if (p != FINGERPRINT_OK) return p;

  p = finger.createModel();
  if (p != FINGERPRINT_OK) return p;

  p = finger.storeModel(id);
  if (p == FINGERPRINT_OK) {
    lcd.clear();
    lcd.print(" Finger Stored!");
    delay(2000);
  }
  return p;
}

int getFingerprintIDez() {
  uint8_t p = finger.getImage();
  if (p != FINGERPRINT_OK) return -1;

  p = finger.image2Tz();
  if (p != FINGERPRINT_OK) return -1;

  p = finger.fingerFastSearch();
  if (p != FINGERPRINT_OK) {
    return -1;
  }
  return finger.fingerID;
}

uint8_t deleteFingerprint(uint8_t id) {
  uint8_t p = finger.deleteModel(id);
  if (p == FINGERPRINT_OK) {
    lcd.clear();
    lcd.print("Finger Deleted");
    delay(1000);
  } else {
    lcd.clear();
    lcd.print("Delete Failed");
    delay(2000);
  }
  return p;
}

void download(int eepIndex) {
  if (EEPROM.read(eepIndex) != 0xff) {
    Serial.print("T->");
    if (EEPROM.read(eepIndex) < 10) Serial.print('0');
    Serial.print(EEPROM.read(eepIndex++));
    Serial.print(':');
    if (EEPROM.read(eepIndex) < 10) Serial.print('0');
    Serial.print(EEPROM.read(eepIndex++));
    Serial.print(':');
    if (EEPROM.read(eepIndex) < 10) Serial.print('0');
    Serial.print(EEPROM.read(eepIndex++));
    Serial.print(" D->");
    if (EEPROM.read(eepIndex) < 10) Serial.print('0');
    Serial.print(EEPROM.read(eepIndex++));
    Serial.print('/');
    if (EEPROM.read(eepIndex) < 10) Serial.print('0');
    Serial.print(EEPROM.read(eepIndex++));
    Serial.print('/');
    Serial.print(EEPROM.read(eepIndex++) << 8 | EEPROM.read(eepIndex++));
  } else {
    Serial.print("---------------------------");
  }
  Serial.print(" ");
}