Keep social distance

INTRODUCTION

As we know that keeping social distance can reduce the risk of getting COVID-19. Here I think we can use Bluetooth beacon RSSI value to calculate the distance between each other. Almost everyone has a smartphone, the best solution is smartphone APP. But I don't know how to program the APP, AI2 doesn't support beacon, I will propose use hardware boards.

System overview

Here I use two LinkIt™ 7697 boards, each one both broadcast iBeacon and scan peripherals. After scan, if find iBeacon device and UUID is matching with preset, calculate the distance. If distance <1.5m lighting LED.

Hardware

LinkIt™ 7697 x 2 : Learn more about Linktit 7697 here.

Software

I combine two example ScanPeripherals and BeaconAdvertisement.

Setting iBeacon at setup function (line 39~49)

//tx
  // configure our advertisement data as iBeacon.
  LBLEAdvertisementData beaconData;

  // This is a common AirLocate example UUID.
  //LBLEUuid uuid("E2C56DB5-DFFB-48D2-B060-D0F5A71096E0");//
  LBLEUuid uuid(keep_distance_UUID);//
  beaconData.configAsIBeacon(uuid, Beacon_major, Beacon_minor, one_meter_RSSI);

  Serial.print("Start advertising iBeacon with uuid=");
  Serial.println(uuid);

  // start advertising it
  LBLEPeripheral.advertise(beaconData);
  //tx end

Loop function scan Beacon and check the device every two seconds.

LBLECentral.scan();
  for(int i = 0; i < 2; ++i)
  {
    delay(1000);
    Serial.print(".");
  }
  warring_flag = 0;
  for (int i = 0; i < LBLECentral.getPeripheralCount(); ++i) {
    printDeviceInfo(i);
  }
  Action(warring_flag);
  LBLECentral.stopScan();

In function printDeviceInfo check devices' UUID. If the same with preset calculate distance.

if(uuid==keep_distance_UUID)
    {
      Serial.println();
      Serial.print("Find someone:");
      Serial.print("\tRSSI:");
      Rssi_AVG=0;
      for (int j = 0; j < RSSI_AVG_cnt; j++) 
      {
        Rssi_AVG += LBLECentral.getRSSI(i);
      }
      Rssi_AVG /= RSSI_AVG_cnt;
      Serial.print(Rssi_AVG);
      Serial.print("\tMajor:");
      Serial.print(major);
      Serial.print("\tMinor:");
      Serial.print(minor);
      distance = calculateAccuracy(txPower,Rssi_AVG);
      if(distance<1.5)
      {
        warring_flag=1;
      }
      Serial.print("\tDistance:");
      Serial.print(distance);
    }

calculate distance code copy from https://stackoverflow.com/a/20434019

static double calculateAccuracy(int txPower, double rssi) 
{
  if (rssi == 0) {
    return -1.0; // if we cannot determine accuracy, return -1.
  }
  double ratio = rssi*1.0/txPower;
  if (ratio < 1.0) {
    return pow(ratio,10);
  }
  else {
    double accuracy =  (0.89976)*pow(ratio,7.7095) + 0.111;    
    return accuracy;
  }
}

If the distance calculated results smaller than 1.5 meters do the action function.

Here I turn on the onboard LED.

void Action(uint8_t flag)
{
  if(flag)
  {
    digitalWrite(LED_PIN, 1);
    Serial.println();
    Serial.println("Warning Keep distance!!!");
  }
  else
  {
    digitalWrite(LED_PIN, 0);
  }
}

After first-time download firmware must calibration one meter RSSI. Use nRF Connect APP to scan and put LinkIt™ 7697 one meter away from the phone. Replace #define one_meter_RSSI -70 with reading data and re-build code download firmware again.

#define one_meter_RSSI -70

Demo

Use Beacon Scanner APP to scan.

I use APP to re-calibrated RSSI value.

Use Serial USB Terminal APP to read serial data from USB.

Since I use the smartphone RSSI value calibrated, the distance calculates have lot of offsets when device to device.

When two devices close each other LED light.

Future Work

Smartphone or wristband APP: can install APP and use it directly without buying another device.

Calculate function improve: from video, RSSI was not stable so the distance wasn't always correct.

Use audio or vibrate as warming:

Reference

https://os.mbed.com/blog/entry/BLE-Beacons-URIBeacon-AltBeacons-iBeacon/#iBeacon

https://docs.labs.mediatek.com/resource/linkit7697-arduino/en