LED and MOTOR “ON” when A BLE DEVICE APPROACH ESP32 MICROCONTROLLER DFR0575

Question

I have this code that is working perfectly but I want my device to start vibrating too (right now only the led is working)

On a Wemos Battery Module I have simply connected the vibration motor on the same PIN of the LED and it works perfectly.

Now I want to do the same on an Beetle ESP32 Microcontroller DFR0575. I used the same code But I can't make the module vibrating (The led light is working perfectly)

this is the code:

 #include <BLEAdvertisedDevice.h>
   #include <BLEDevice.h>
   #include <BLEScan.h>

   const int PIN = 2;
   const int CUTOFF = -50;


   void setup() {
     pinMode(PIN, OUTPUT);
     BLEDevice::init("tkr");
   }

   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);
   }

Answer 1

It is generally very dangerous to drive any motor directly from a digital output pin. Motors often need way more current, than the digital pin can provide. Based on the answer to this question, an ESP8266 can provide 20mA or 12mA depending on current direction (may be a bit different for an ESP32, but not substantially). Drawing more current, than the pin can provide, can lead to the destruction of the output hardware of the pin. It is not easy to say, when this will happen, because it depends not only on the current draw, but also on time and fabrication variation.

Also a motor is an inductive load, which means, that fast changes (for example turning on and off) will induce a reverse voltage in the motor coils. These can easily be very high relative to the supply voltage and thus destroy you output pin or even the complete microcontroller.

I cannot give you a full reasoning, why it works with the first board, but not with the second. I think, it has to do with the above.

You should always do 2 things, when driving motors with a microcontroller:

1. Use a motor driver circuit: You can either buy a ready to use motor driver or you can build one yourself. If you only want to turn the motor in one direction (as with a vibration motor), all you need is a MOSFET, which will act as a switch between the motor and the power supply. This switch get's controlled by the Arduino's output pin (which only needs to supply a very low current for switching). You can google "MOSFET as a switch". Be sure to use a MOSFET, that can provide the needed current and that is good in saturation for the used gate voltage (the working voltage of the microcontroller).

2. Use a flyback diode: The reverse induction voltage can also hurt MOSFETs. You want to let these voltage spikes quickly plenish by letting the current flow to ground. You can do this with a flyback diode. That is a diode, that bridges drain and source of the MOSFET. It is oriented so that block for normal operation (the normal positive supply voltage). When the MOSFET get's turned off, a great negative voltage will build up in the motor, but since the diode is conducting in this way, the voltage will safely flow to ground, so that the induction voltage cannot hurt the other electronic parts.