___________ P_R_O_G_R_A_M_M_I_N_G ___________
| OVERVIEW OF BLE COMMUNICATION |
For the Communication between the room's Beacons and the actuators (Vibration Motors and Solenoids) on the Tactile Map. I decided to use the BLE (Bluetooth Low Energy) Communication Protocol.
In this architecture, the Beacons will work as Servers that emit signals ( in my case, I specifically need them to send their Address and the stregth of their signal, called RSSI - Received Signal Strength Indication -.
The ESP32 inside the Tactile Map, instead, will act as a Scanner that detects incoming signals and translates them into the activation of the actuators (vibration Motors and Solenoids).
To be more specific, these incoming signals that the Scanner will detect are going to be each Beacon's Address and its RSSI. Then the Scanner will pick the nearest Beacon (the one with the strongest RSSI) and activate the matched actuators:
- Vibration Motors: will vibrates the corner section of the map where the room is located
- Solenoid under the selected room will come up. After having setting my 3 Bluetooth modules as Beacons, the thing I needed to focus was creating the Scanner code.
| ESP32 BLE Library for Arduino IDE |
For creating the Scanner code, since I used the ESP32 Microcontroller for my PCB, I needed to install the required ESP32 BLE Library for Arduino IDE.
I found a really well explained guide for installing it here.
After having installing it, on Arduino IDE I opened the BLE Scanner_sketch_example by clicking on FILE -> Examples -> ESP32 BLE Arduino -> BLE_scan.
After having uploading the sketch, this appeared on the Serial Port:
Advertised Device: Name: , Address: 59:b0:4b:4b:2a:cc, manufacturer data: 4c001005131ce31b6a, txPower: 12
Advertised Device: Name: , Address: d4:36:39:dc:12:c6, manufacturer data: 4c00021574278bdab64445208f0c720eaf0599351234fa02c5
47Devices found: 2
Scan done!
I only needed the Addresses and also finding a function to get the RSSI of my beacons. So, the next step was changing the Callback Routine example for my purpose.
| Returning Beacon's ADDRESS and RSSI |
With the kind help of my instructor Simone Guercio, I analysed the Espressif ESP32 reference guide for the BLEAdverticeDevice.h library, which we found poorly documented.
Anyway, we managed to find the functions for getting the Addresss and RSSI that I was interested in:
- BLEAdvertisedDevice::getAddress() = to obtain the address of the advertised device.
- int BLEAdvertisedDevice::getRSSI() = to obtain the RSSI of the advertisedDevice .
To do so, I set up an Addresses String, a RSSIvalues arrey, and a Beacons arrey.
In the Callbacks routine I used a for() statement to initialize all the elements in the StringAddresses, Arrey RSSIvalues and Beacons.
What I wanted to do was for the Scanner to be able to recognize the known Addresses of my Beacons out of all the other devices that he would found. So I followed this kind of logic:
If the Scanner, during its routine finds a "BLEAdvertisedDevice::getAddress()" that is equal to the knownAddresses of my Beacons [i],
then he found my Beacons.
If he found my Beacons, then the RSSI that he finds with the getRSSI() is the RSSIvalue[i].
Here is the code just for the new Callbacks Routine:
In the image below you can see what happened in the Serial Monitor:
The yellow Addresses where my Beacons Addresses.
The Scanner recognised them. Gave the corrisponded index and which beacon had detected.
| Finding the MAX RSSI value |
After defining my new Callbacks Routine. I needed to compare the 3 RSSI values to find the major values.
I did that inside the void Loop().
I also decided to test the code using LEDS. So I matched each LED to a Beacon. The aim was to make the LED of the nearest Beacon turn on.
To connect the LEDs to the Adafruit ESP32 Huzzah Feather I searched on the ESP32 GPIO & Analog Pins datasheet section and I found that I could use every pin except for A2/GPI #34, A3/GPI #39, and A4/GPI #36, which are IMPUT pins only.
I decided to use GPIO #27, #15, #14 for the 3 LEDs.
Here is the full sketch:
| Final Sketch & Test |
After milling and soldering my board with the ESP32 module, I decided to write the final code adding my actuators (vibration motors and solenoids) to the loop.
Here is the final sketch:
And the final test (if you turn up the audio on full volume you can also hear the vibration motors.
