How to increase beacon scan sample rate use esp32 - bluetooth-lowenergy

Question

I using the esp32 to detection beacon through rssi of beacon, but i meet some problem, first is rssi value is no stable so i need more sample of rssi, the second problem is esp32 scan sample rate is too slow, that faster speed only have one second scan rate, below is my used code
#include <BLEAdvertisedDevice.h>
#include <BLEDevice.h>
#include <BLEScan.h>
const int PIN = 2;
const int CUTOFF = -60;
void setup() {
pinMode(PIN, OUTPUT);
BLEDevice::init("");
}
void loop() {
BLEScan *scan = BLEDevice::getScan();
scan->setActiveScan(true);
BLEScanResults results = scan->start(1);
int best = CUTOFF;
for (int i = 0; i < results.getCount(); i++)
{
BLEAdvertisedDevice device =
results.getDevice(i);
int rssi = device.getRSSI();
if (rssi > best) {
best = rssi;
}
}
digitalWrite(PIN, best > CUTOFF ? HIGH :
LOW);
}
but i want to mor rssi sample, i tried change scan->start(1) to scan->start(0), but result is not return, how to do can solve lower sample problem, or use another board?

Answer 1

The problem is that you do all of the "work" in the loop.
Are you aware of the fact that an ESP32 microcontroller runs at 240 MHz
I guess your loop time is about 400 Nano seconds.
So how would your device know if and how much devices are found.
You are trying to do something with the scan results just after scan start.
To get around this problem there is a BLEAdvertisedDeviceCallbacks in the Arduino for ESP32 code.
This callback will return a result for every device it finds.
Here is an example from GITHUB (ESP32_BLE_Arduino by Neil Kolban)https://github.com/nkolban/ESP32_BLE_Arduino/blob/master/examples/BLE_scan/BLE_scan.ino
/*
Based on Neil Kolban example for IDF: https://github.com/nkolban/esp32-snippets
/blob/master/cpp_utils/tests/BLE%20Tests/SampleScan.cpp
Ported to Arduino ESP32 by Evandro Copercini
*/
#include <BLEDevice.h>
#include <BLEUtils.h>
#include <BLEScan.h>
#include <BLEAdvertisedDevice.h>
int scanTime = 5; //In seconds
BLEScan* pBLEScan;
class MyAdvertisedDeviceCallbacks: public BLEAdvertisedDeviceCallbacks {
void onResult(BLEAdvertisedDevice advertisedDevice) {
Serial.printf("Advertised Device: %s \n", advertisedDevice.toString().c_str());
}
};
void setup() {
Serial.begin(115200);
Serial.println("Scanning...");
BLEDevice::init("");
pBLEScan = BLEDevice::getScan(); //create new scan
pBLEScan->setAdvertisedDeviceCallbacks(new MyAdvertisedDeviceCallbacks());
pBLEScan->setActiveScan(true); //active scan uses more power, but get results
//faster
pBLEScan->setInterval(100);
pBLEScan->setWindow(99); // less or equal setInterval value
}
void loop() {
// put your main code here, to run repeatedly:
BLEScanResults foundDevices = pBLEScan->start(scanTime, false);
Serial.print("Devices found: ");
Serial.println(foundDevices.getCount());
Serial.println("Scan done!");
pBLEScan->clearResults(); // delete results fromBLEScan buffer to release memory
delay(2000);
}
This to give you an idea on how it works, tweak it to meet your own needs.