The bracelet has 3 operating modes: Battery charging mode, Finger vibration mode, Sound mode.

- "Button" is used to turn the device on or off by pressing and holding for 3 seconds. Or to switch between two modes, finger vibration mode or sound mode.

- Pc817 has function to close circuit to A2 pin measure battery voltage.

- Relay has a function to turn on / off the power from the battery with charging feet and Arduino.

water plastic pipe ∅21mm and ∅48

And it fit the size of my hand

I cut a lot of small plastic sheets, to fit into the box shape, then use plastic glue to connect them

Now try wearing it on your hand. Looks pretty okay

Use plastic glue to connect them.

//tác giả: Đỗ Xuân Tiến
#include <EEPROM.h>
const int trig = 8;     //chân trig của HC-SR04
const int echo = 7;     //chân echo của HC-SR04

byte ngon_tay_cai_6 = 6;     //ngón tay cái - thumb
//byte middle_finger = 5;  //ngón tay giữa
byte ngon_tay_ut_3 = 3;      //ngón tay út - little finger
byte relay_A0 = A0;     //relay 3v3a
byte button_A3 = A3;    //button
byte coi_chip_10 = 10;  //buzzer
byte led_11 = 11;       //led
byte opto_volt_pin_12 = 12; //opto pc817
byte do_volt_out_A1 = A1; //Check whether the charger is charging or not 
byte do_volt_pin_A2 = A2; //Measure the battery voltage

byte rung_cai = 0; 
byte rung_ut = 0;
byte rung_cai_1 = 0;    
byte rung_cai_2 = 0;
byte rung_ut_1 = 0;     
byte rung_ut_2 = 0;
byte che_do_rung = 0; 
byte khong_lap = 0;   
byte sau_tha_nut = 0;     
byte loa1 = 0;  
byte loa2 = 0; 
byte den1 = 0;  
byte den2 = 0; 
byte tat = 0;  //biến giúp khi rút sạc thì tắt - Turn off the power when not charging

int dovolt_out = 0;
float volt_out = 0;

unsigned long pe_rung = 0;
unsigned long pe_rung_cai_1 = 0;   
unsigned long pe_rung_cai_2 = 0; 
unsigned long pe_rung_ut_1 = 0;    
unsigned long pe_rung_ut_2 = 0;
unsigned long pe_loa1 = 0;   
unsigned long pe_loa2 = 0; 
unsigned long pe_nhanli = 0;
unsigned long pe11 = 0;   
unsigned long pe12 = 0;          

int GT_button = 0;
int GT_button_000 = 0;
int time_x = 0;

void tien_sacpin (unsigned long giay)
{ 
  unsigned long peham_sac = millis(); 
  while((millis() - peham_sac <= giay) && (volt_out >= 3.5)){
        //đo volt ngoài 
        dovolt_out = analogRead(do_volt_out_A1);                                          
        volt_out = dovolt_out / 1023.0 * 5.0;
        //nháy đèn
        if((den1 == 0) && (millis() - pe12 >= 150)){pe11 = millis(); digitalWrite(led_11,HIGH); den1 = 1; den2 = 0;}   
        if((den2 == 0) && (millis() - pe11 >= 150)){pe12 = millis(); digitalWrite(led_11,LOW); den2 = 1; den1 = 0; }  
             
  }
} 
void setup()
{
    pinMode(relay_A0,OUTPUT);
    digitalWrite(relay_A0,HIGH);
    
    //Serial.begin(9600);     // giao tiếp Serial với baudrate 9600
    pinMode(trig,OUTPUT);   // chân trig sẽ phát tín hiệu
    pinMode(coi_chip_10,OUTPUT);
    pinMode(ngon_tay_cai_6,OUTPUT);
    pinMode(ngon_tay_ut_3,OUTPUT);
    pinMode(opto_volt_pin_12,OUTPUT);
    pinMode(led_11,OUTPUT);
    pinMode(echo,INPUT);    // chân echo sẽ nhận tín hiệu
    pinMode(button_A3,INPUT);
    pinMode(do_volt_out_A1,INPUT);
    pinMode(do_volt_pin_A2,INPUT);
    
    delay(6000);
     
    che_do_rung = EEPROM.read(6);
    delay(200);
    if((che_do_rung != 1) && (che_do_rung != 0)){delay(1000); EEPROM.write(6, 0); delay(1000); che_do_rung = EEPROM.read(6);}      //quan trọng, chỉ dùng 1 lần - Only run once

 
}
 
void loop()
{ 

//đo volt ngoài - Check whether the charger is charging or not 
  dovolt_out = analogRead(do_volt_out_A1);                                          
  volt_out = dovolt_out / 1023.0 * 5.0;  
  //Serial.println(volt_out);

//chế độ sạc pin - Battery charging mode
  if(volt_out >= 3.5){tat = 1;} //biến giúp khi rút sạc thì tắt - "tat = 1: Turn off the power when not charging"
while((volt_out >= 3.5) or (tat == 1)){
  
  digitalWrite(coi_chip_10,LOW);
  analogWrite(ngon_tay_cai_6,0);
  analogWrite(ngon_tay_ut_3,0);

  //đo volt ngoài - Check whether the charger is charging or not  
  dovolt_out = analogRead(do_volt_out_A1);                                          
  volt_out = dovolt_out / 1023.0 * 5.0;
  
  digitalWrite(led_11,LOW);    
  digitalWrite(relay_A0,LOW);   
  digitalWrite(opto_volt_pin_12,HIGH);
  delay(3500);
  //đo volt pin - Measure the battery voltage
  int dovolt_pin = analogRead(do_volt_pin_A2);                                          
  float volt_pin = dovolt_pin / 1023.0 * 5.0;  
  //Serial.println("pin_1");
  //Serial.println(volt_pin);
  //Serial.println("pin_2");
  if(volt_pin <= 4.9){digitalWrite(relay_A0,HIGH); tien_sacpin(60000);}
    else{digitalWrite(led_11,HIGH); delay(500);}
  
  }

digitalWrite(relay_A0,HIGH);
digitalWrite(opto_volt_pin_12,LOW);

    if((den1 == 0) && (millis() - pe12 >= 1500)){pe11 = millis(); digitalWrite(led_11,HIGH); den1 = 1; den2 = 0;}   
    if((den2 == 0) && (millis() - pe11 >= 1500)){pe12 = millis(); digitalWrite(led_11,LOW); den2 = 1; den1 = 0; }

//chế độ không sạc pin - No battery charging mode  
if(volt_out < 3.5){
  //nhấn lỳ 3s để tắt - Hold down for 3 seconds to turn off    
      GT_button = digitalRead(button_A3);      
  if (GT_button != GT_button_000) 
     { GT_button_000 = GT_button;                              
       pe_nhanli = millis();              
      }
  if ((GT_button == 1) && (millis() - pe_nhanli > 3000)){digitalWrite(coi_chip_10,HIGH); digitalWrite(led_11,HIGH); 
                                                         analogWrite(ngon_tay_cai_6,100); analogWrite(ngon_tay_ut_3,100); delay(500); digitalWrite(coi_chip_10,LOW);
                                                         delay(5000); digitalWrite(relay_A0,LOW); delay(5000);}

  //nhấn nhanh để chuyển đỗi gữa loa và rung, Đọc trạng thái button để bật loa hoặc bật rung - Quick click to switch speakers and vibrate
 GT_button = digitalRead(button_A3);   
   
 if((GT_button == 1) && (khong_lap == 0)){ khong_lap = 1; sau_tha_nut = 1; }  
  
 if((GT_button == 0) && (sau_tha_nut == 1)){sau_tha_nut = 0; khong_lap = 0; che_do_rung = EEPROM.read(6);delay(10);
                                            if(che_do_rung == 1){delay(300); EEPROM.write(6, 0); delay(300);}
                                              else{delay(300); EEPROM.write(6, 1); delay(300); }
                                              che_do_rung = EEPROM.read(6); }

    
    unsigned long thoi_gian = 0; // biến đo thời gian - Time variable
    int khoang_cach;           // biến lưu khoảng cách - Distance variable


    /* Phát xung từ chân trig */
    delay(50);  //delay tránh nhiễu sóng siêu âm
    digitalWrite(trig,0);   // tắt chân trig
    delayMicroseconds(2);
    digitalWrite(trig,1);   // phát xung từ chân trig
    delayMicroseconds(5);   // xung có độ dài 5 microSeconds
    digitalWrite(trig,0);   // tắt chân trig
    
    /* Tính toán thời gian */ 
    thoi_gian = pulseIn(echo,HIGH);

    // Tính khoảng cách đến vật.
    khoang_cach = int(thoi_gian/2/29.412);
    
    //Serial.print(khoang_cach);
    //Serial.println("cm");

    if(khoang_cach <= 130)                         {rung_cai = 1; rung_ut = 0; pe_rung = millis();}
    if((khoang_cach > 130) && (khoang_cach <= 280)){rung_cai = 0; rung_ut = 1; pe_rung = millis();}
      else{if(millis() - pe_rung >= 1000){rung_cai = 0; rung_ut = 0;}}

//chế độ rung ngón tay - finger vibration mode
if(che_do_rung == 0){
    if(millis() - pe_loa1 >= 50){digitalWrite(coi_chip_10,LOW);}
      
    // rung nhẹ ngón tay cái - Motor vibration on the thumb
    if(rung_cai == 1){if((rung_cai_1 == 0) && (millis() - pe_rung_cai_2 >= 100)){pe_rung_cai_1 = millis();analogWrite(ngon_tay_cai_6,150); rung_cai_1 = 1; rung_cai_2 = 0;}   //rung có nhịp
                      if((rung_cai_2 == 0) && (millis() - pe_rung_cai_1 >= 300)){pe_rung_cai_2 = millis();analogWrite(ngon_tay_cai_6,0); rung_cai_2 = 1; rung_cai_1 = 0; }}
      else{analogWrite(ngon_tay_cai_6,0);}
    
    // rung nhẹ ngón tay út - Vibration motor on the little finger 
    if(rung_ut == 1){if((rung_ut_1 == 0) && (millis() - pe_rung_ut_2 >= 100)){pe_rung_ut_1 = millis();analogWrite(ngon_tay_ut_3,150); rung_ut_1 = 1; rung_ut_2 = 0;}   //rung có nhịp - Vibration motor feel comfortable
                     if((rung_ut_2 == 0) && (millis() - pe_rung_ut_1 >= 300)){pe_rung_ut_2 = millis();analogWrite(ngon_tay_ut_3,0); rung_ut_2 = 1; rung_ut_1 = 0; }}
      else{analogWrite(ngon_tay_ut_3,0);}
   }

//chế độ phát loa, nháy loa nhanh dần khi khoảng cách giảm dần - Sound mode
  else{
    analogWrite(ngon_tay_cai_6,0);
    analogWrite(ngon_tay_ut_3,0);

    if(khoang_cach <= 300){ time_x = (2 * khoang_cach) + (khoang_cach / 2);
                            if((loa1 == 0) && (millis() - pe_loa2 >= time_x)){pe_loa1 = millis();digitalWrite(coi_chip_10,HIGH); loa1 = 1; loa2 = 0;}   
                            if((loa2 == 0) && (millis() - pe_loa1 >= 50))    {pe_loa2 = millis();digitalWrite(coi_chip_10,LOW); loa2 = 1; loa1 = 0; }
      }
      else{if(millis() - pe_loa1 >= 30){digitalWrite(coi_chip_10,LOW);}}

    //nháy loa nhanh khi khoảng cách đến vật khoảng 1m
    //if(rung_cai == 1){ if((loa1 == 0) && (millis() - pe_loa2 >= 60)){pe_loa1 = millis();digitalWrite(coi_chip_10,HIGH); loa1 = 1; loa2 = 0;}   
    //                   if((loa2 == 0) && (millis() - pe_loa1 >= 60)){pe_loa2 = millis();digitalWrite(coi_chip_10,LOW); loa2 = 1; loa1 = 0; }}

    //nháy loa chậm khi khoảng cách đến vật từ 1m đến 2.8m
    //if(rung_ut == 1) { if((loa1 == 0) && (millis() - pe_loa2 >= 500)){pe_loa1 = millis();digitalWrite(coi_chip_10,HIGH); loa1 = 1; loa2 = 0;}   
    //                   if((loa2 == 0) && (millis() - pe_loa1 >= 80)){pe_loa2 = millis();digitalWrite(coi_chip_10,LOW); loa2 = 1; loa1 = 0; }}
    //
    //if((rung_cai == 0) && (rung_ut == 0)){if(millis() - pe_loa1 >= 60){digitalWrite(coi_chip_10,LOW);}}
        
   }                                   
 }
 
}

I solder the tin between two Arduino circuits with hc-sr04 through their GND pin. As in the picture, red circle. The circuit will be fixed firmly !

Try putting it in the box, there's still a good gap for the rest.

Use glue to bond vibrating motor with small ring.

Vibrator Motor can be purchased at the telephone repair shop.

After the electrical part is completed.

I use 2 screws for the bottom of the box.

Thank you!!!

I use elastic fabric to wrap the bracelet. Can take advantage of the socks.

The bracelet adjustable to fit more people's hands. The strap taken from a broken helmet.

Can wear medium with the hands of more people.

Thank you!!!