Arduino Nano 33 BLE Bluetooth Wake trigger

Official Hardware Nano Family Nano 33 BLE
1

Hi
I'm developing a smart lock via bluetooth, but I'm having a hard time lowering power consumption.
So far I managed to reduce the consumption to 3ma by cutting the 3.3v jumper, feeding the arduino through the 3v3 port and running this code:

#include <mbed.h>
#include <rtos.h>
#include <ArduinoBLE.h>
#include <nrf_power.h>

int count = 0;
int isConnected = 0;

BLEService ledService("9eea8d70-6891-48c1-a4b4-c4b7177f6c37");
BLEStringCharacteristic switchCharacteristic("6e2d2a65-9484-4608-823e-0ab076adefe6", BLENotify | BLEWrite, 100);

void setup() {
  nrf_uarte_task_trigger(NRF_UARTE0, NRF_UARTE_TASK_STOPRX);
  while (!nrf_uarte_event_check(NRF_UARTE0, NRF_UARTE_EVENT_RXTO)) ;

  NRF_UARTE0->ENABLE = 0;
  NRF_UART0->ENABLE = 0;
  nrf_power_dcdcen_set(true);

  digitalWrite(LED_BUILTIN, LOW);
  digitalWrite(LED_PWR, LOW);
  digitalWrite(PIN_ENABLE_SENSORS_3V3, LOW);
  digitalWrite(PIN_ENABLE_I2C_PULLUP, LOW);

  startBle();
}

void loop() {
  while (count < 500) {
      BLE.poll();
      count++;
    }
    if (isConnected == 0) {
      rtos::ThisThread::sleep_for(1000);
    }
    count = 0;
}

void startBle() {
    BLE.begin();
    BLE.setLocalName("low-power-device");
    BLE.setAdvertisedService(ledService);
    ledService.addCharacteristic(switchCharacteristic);
    BLE.addService(ledService);
    BLE.setEventHandler(BLEConnected, blePeripheralConnectHandler);
    BLE.setEventHandler(BLEDisconnected, blePeripheralDisconnectHandler);
    switchCharacteristic.setEventHandler(BLEWritten, switchCharacteristicWritten);
    switchCharacteristic.setValue("");
    BLE.advertise();
}


void blePeripheralConnectHandler(BLEDevice central) {
  isConnected = 1;
}

void blePeripheralDisconnectHandler(BLEDevice central) {
  isConnected = 0;
}

void switchCharacteristicWritten(BLEDevice central, BLECharacteristic characteristic) {
  //verify data and open door
}

But I need the arduino to have the minimum consumption because the lock works with AAA batteries.
The only alternative I've found so far is to use the command:

NRF_POWER->SYSTEMOFF = 1;

and give a physical pulse on the Arduino reset.

The theoretical idea would be to have the BLE module work independently from the main processor in a advertising mode and when it receives a connection start the rest of the board to run the code.

2

The Arduino Nano 33 BLE uses the nRF52840 inside the BLE module. Most of the BLE stack runs on the Cortex-M4 processor where your sketch runs as well. Only the low layer stuff is handled directly in the radio.

You can have a look at the nRF52840 data sheet and then work your way trough all the peripherals and see what is active. There is also a chapter (5) on power management and current consumption.

3

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