This last block uses the clock function to check every second wether there is a message received over Bluetooth. If a message is received it is displayed in Label2.

And that completes the App for your phone.

If you do not want to compose all the blocks yourself I have a copy of the above code available for you to download here:

https://www.mediafire.com/file/554kyre473onlh0/Pico_bluet_SR.aia/file

The Python program for the Pico.

Now we have a complete app available that can send and receive data over Bluetooth let's look at the Pico side. Here is the complete MicroPython program.

import os
import utime
from machine import UART, Pin
#print sys info
print(os.uname())
L1 = Pin(14,Pin.OUT)
L2 = Pin(13,Pin.OUT)
L3 = Pin(12,Pin.OUT)
L4 = Pin(11,Pin.OUT)
#indicate program started visually
led_onboard = machine.Pin(25, machine.Pin.OUT)
led_onboard.value(1) # onboard LED ON for 0.5 sec
utime.sleep(0.5)
led_onboard.value(0) # onboard LED ON for 0.5 sec
uart = machine.UART(0, baudrate=9600,
 bits=8, parity=None, stop=1)
print(uart)
uart.write("hello")
utime.sleep(1)
uart.write("The temperature is : ")
uart.write(str(35))
L1.value(1)
utime.sleep(1)
L1.value(0)
L2.value(1)
utime.sleep(1)
L2.value(0)
L3.value(1)
utime.sleep(1)
L3.value(0)
L4.value(1)
utime.sleep(1)
L4.value(0)
while True:
 b=""
 a=""
 c=""
 while a != "#" :
 a = uart.read(1)
 c = (a.decode('utf-8'))
 a = c
 if (c != "#"):
 b = b + c
 print("received chars: ",len(b)," = ",b)
 
 if "on1" in b:
 L1.value(1)
 uart.write("Led 1 On")
 if "off1" in b:
 L1.value(0)
 uart.write("Led 1 Off")
 
 if "on2" in b:
 L2.value(1)
 uart.write("Led 2 On")
 if "off2" in b:
 L2.value(0)
 uart.write("Led 2 Off")
 if "on3" in b:
 L3.value(1)
 uart.write("Led 3 On")
 if "off3" in b:
 L3.value(0)
 uart.write("Led 3 Off")
 
 if "on4" in b:
 L4.value(1)
 uart.write("Led 4 On")
 if "off4" in b:
 L4.value(0)
 uart.write("Led 4 Off")

As usual I will show how this program works by highlighting certain parts.

import os
import utime
from machine import UART, Pin

L1 = Pin(14,Pin.OUT)
L2 = Pin(13,Pin.OUT)
L3 = Pin(12,Pin.OUT)
L4 = Pin(11,Pin.OUT)

#indicate program started visually
led_onboard = machine.Pin(25, machine.Pin.OUT)
led_onboard.value(1) # onboard LED ON for 0.5 sec
utime.sleep(0.5)
led_onboard.value(0) # onboard LED ON for 0.5 sec

uart = machine.UART(0, baudrate=9600,
 bits=8, parity=None, stop=1)
print(uart)

These lines define the serial communication's settings and display them in Thonny's shell when the program runs.

uart.write("hello")
utime.sleep(1)
uart.write("The temperature is : ")
uart.write(str(35))

This is a test in which we send a fake message to the phone. First the word "hello"is send and next "The temperature is 35" As you can see the last line converts the number 35 into a string that can be send over Bluetooth.

L1.value(1)
utime.sleep(1)
L1.value(0)
L2.value(1)
utime.sleep(1)
L2.value(0)
L3.value(1)
utime.sleep(1)
L3.value(0)
L4.value(1)
utime.sleep(1)
L4.value(0)

The leds are all set on and then off as a test so we can see they are working and attached to the right I/O pins.

Then comes the most important part of the program. It is where an incoming message from the Phone is read and decoded.

while True:
 b=""
 a=""
 c=""
 while a != "#" :
 a = uart.read(1)
 c = (a.decode('utf-8'))

 a = c
 if (c != "#"):
 b = b + c
 print("received chars: ",len(b)," = ",b)

 if "on1" in b:
 L1.value(1)
 uart.write("Led 1 On")
 if "off1" in b:
 L1.value(0)
 uart.write("Led 1 Off")

In the field

A new screen opens showing all Bluetooth devices available and the ones that you have used in the past. The top one has the Bluetooth adress and name (HC-06) we want to connect to. Press on that line and the connection is made.

Now you can use the app and switch the led's on and off.

This clearly demonstrates how to receive data from Bluetooth and how to send data over Bluetooth.

Of course this is just a framework to send and receive all kinds of data from your phone to the Raspberry Pico and the other way round.

For more detailed info on the Raspberry Pi Pico, a short course on MicroPython and using all kinds of sensors with the Pico please buy my book Raspberry Pi Pico Simplified: https://lucstechblog.blogspot.com/2021/08/raspberry-pi-pico-simplified-now.html

Till next time
have fun

Luc Volders

For an index to all my stories click this text.

This is the second story on how to use Bluetooth Classic with the ESP32. The first story covered how to send data from an Android App to the ESP32. You can re-read that story here:
http://lucstechblog.blogspot.com/2024/07/esp32-bluetooth-classic-part-1.html

This story expands the previous one and shows how to display sensor data on your phone's screen. In the first story I build an Android App with MIT's App Inventor. And I am going to modify that app for receiving data from the ESP32.

The hardware

As this is a tutorial and a base for using Bluetooth with the ESP32 I am going to attach two sensors to the ESP32 for generating data. The first one is a simple button and the second one is a Dallas DS18B20 digital thermometer chip. You can easily replace these with any other sensor you might have laying around.

For testing purposes I always build my projects on a breadboard and this is how that looks.



In the previous story I attached a led to D5 with a current delimiting resistor and that is still there. Use this for testing if sending a command from Android to the ESP is still working.

The Dallas DS18B20 is attached to a pull-up resistor and to D19 at the ESP32

Then there is a simple push-button which is connected to D21. I did not use a pull-up resistor on the button but will use the internal pull-up resisitor from the ESP32.

The App Inventor App

As we want to display the values of the button and the digital thermometer we need to add a field to our app's screen. I am just adding one field and the data will be displayed on alternate turns in that field.

So I added a new Label to the screen called Label2



On the left side of the screen click on Label and drag that to your screen. In my sample I put the new Label just above my ridiculous copyright label. The picture shows it as the rectangle.

Next step is to click on "Sensors" at the right side of the screen and click on the Clock sensor and drag that into your screen. It will then appear at the bottom as a non-visible component.
The clock is standard set to fire a signal every second. You can change that to your liking by clicking on the clock icon and then change the properties section at the right side of the designer (not seen in the above picture).

Now move over to the blocks section.



The complete blocks are almost identical to those of the previous story. The only modification is a new block used for receiving data.



This block is executed every second (remember, the property from the clock). First the bluetooth connection is tested and then the text in Label2 is set to the received information.

That is all.
Please delve deeper into App Inventor if you want to make alterations or add more functionality to this simple app. A bit of studying on App Inventor will show that it is fun to play with and easy to develop app's with.

Build the App. Download it to your computer and then transfer it over USB to your phone and install it.

The ESP32 Program

Basically this is the same program as the one from the previous story with some alterations. Let's have a look at the whole program.

#include <OneWire.h>
#include <DallasTemperature.h>
#include "BluetoothSerial.h"
#if !defined(CONFIG_BT_ENABLED) || !defined(CONFIG_BLUEDROID_ENABLED)
#error Bluetooth is not enabled! Please run `make menuconfig` to and enable it
#endif
BluetoothSerial SerialBT;
#define ONE_WIRE_BUS 19
OneWire oneWire(ONE_WIRE_BUS);
DallasTemperature dallas(&oneWire);
String Charrcvd;
String text;
int led=5;
int button=21;
void setup() 
{
 Serial.begin(115200);
 SerialBT.begin("ESP32BTtest"); //Bluetooth device name
 Serial.println("Bluetooth started, now pair your phone");
 pinMode(led, OUTPUT);
 pinMode(button, INPUT_PULLUP);
}
void loop() 
{
 /* 
 * -----------------------------------
 * Bluetooth send part 
 * -----------------------------------
 */
 if(digitalRead(button) == 1)
 { 
 dallas.requestTemperatures();
 SerialBT.print("Temp: ");
 SerialBT.println(dallas.getTempCByIndex(0));
 Serial.println(dallas.getTempCByIndex(0));
 delay(1000);
 }
 else
 {
 SerialBT.println("Button pressed");
 delay(1000);
 SerialBT.println(" ");
 }
 /* 
 * ----------------------------------
 * Bluetooth receive part
 * ----------------------------------
 */
 if (SerialBT.available()) 
 {
 Charrcvd = SerialBT.readString();
 {
 text = text + Charrcvd;
 }
 }
 if (text != "")
 {
 Serial.println(text.substring(0,text.length()-1));
 Serial.println(text.length());
 if (text.substring(0,text.length()-1)== "On") 
 {
 Serial.println("Received: On");
 digitalWrite(led, HIGH);
 }
 if (text.substring(0,text.length()-1)== "Off") 
 {
 Serial.println("Received: Off");
 digitalWrite(led, LOW);
 }
 text = "";
 delay(20);
 }
}

#include <OneWire.h>
#include <DallasTemperature.h>

#define ONE_WIRE_BUS 19

OneWire oneWire(ONE_WIRE_BUS);
DallasTemperature dallas(&oneWire);

 if(digitalRead(button) == 1)
 { 
 dallas.requestTemperatures();
 SerialBT.print("Temp: ");
 SerialBT.println(dallas.getTempCByIndex(0));
 Serial.println(dallas.getTempCByIndex(0));
 delay(1000);
 }

 else
 {
 SerialBT.println("Button pressed");
 delay(1000);
 SerialBT.println(" ");
 }

For an index to all my stories click this text.

For communication with an ESP32 we mostly use Wifi. Wifi is easy to use and almost everywhere available. However there are times when you do not want or can use wifi. An example is when you are walking or biking in a rural environment. When this is the case you can communicate through Bluetooth with the ESP32.

Two kinds of Bluetooth.

There are two kinds of Bluetooth. There is normal Bluetooth called Classic Bluetooth and there is Bluetooth Low Energy (BLE for short). Classic Bluetooth was the first and is still used. With Classic Bluetooth you can send audio and large amounts of data (like music, apps, photo's etc) to another Bluetooth device. So when you are pairing your phone with headphones you will be using Classic Bluetooth. This uses more power as BLE.
Bluetooth Low Energy (BLE) uses far less energy (duh !!) and can transmit data over a longer range. The setback is that it can only send small amounts of data so no music or photo's. But it is excellent for sending sensor data etc.

This story focusses on sending data from your Android Phone to an ESP32 using Classic Bluetooth.

MIT's App Inventor

If you want to develop App's for your Android Phone in a quick and easy to learn way I recommend MIT's App Inventor. I have used this many times in previous stories dating back to my first Android App in 2015:
http://lucstechblog.blogspot.com/2015/04/wijnmaker-app-many-years-ago-i-started.html

More stories can be found on my index page:
http://lucstechblog.blogspot.com/p/index-of-my-stories.html
Check them out for learning more about building your own apps. You can go straight to MIT's App Inventor by this link: https://appinventor.mit.edu/

I must admit that the last year I have been studying different ways to build apps for your phone. The first one is by building Javascript programs and turning them into an App. Which has been covered on this weblog in previous stories. And there is B4X which is a totally different programming language that turns a Basic-like scripting language into native Java. This last one is much more difficult to learn for beginners but produces Apps which are about 1/3 the size of an App made with MIT's App Inventor. I will be covering B4X in a future story. If you are curious though, check it out at https://www.b4x.com/

For now we stick to MIT's App Inventor.

The example

I am showing a simple setup. A led connected to the ESP32 and a simple App with a button to choose the available Bluetooth device and two buttons to set the led On and Off.

The hardware setup.

Nothing Special here.

Just the Doit ESP32 Devkit connected to a led (with a current delimiting resistor of 220 Ohm) on pin D5.

Designing the App

I can not give a complete tutorial on App Inventor here as it is to comprehensive. So I'll just give a brief discussion on how it is done. If you need to know more look at my other stories on App Inventor or follow the tutorials on their website and the many examples that can be found on Youtube etc. You can find App Inventor here: https://appinventor.mit.edu/

Sign in with your google account and start a new project.

In the Designer set the Background color of the screen to Blue.



Add two buttons. Set the text to the first button to: Led on and make the text white. Set the background to green. The text of the second button is set to Led Off and the background is set to Red. Size them to your liking.

At the top of the page a ListPicker element is created with black Textcolor and a white background with the text "Pick your Bluetooth device"

Below the buttons I put a label with a yellow text saying "(c) Luc Volders 2022" which is off course bullshit but gives the app a nice touch.

From the Connectivity items (at the left part on the screen) add BlueToothClient and from the User Interface items add Notifier. These will not be visible on the screen but work in the background.

That is it.
On to the Blocks section.



Let's have a look at the individual blocks.



The ListPicker does it's job right when the app starts.
The Listpicker checks all available Bluetooth clients and puts the names and Bluetooth adresses in a list.



If you click on the ListPicker a new screen opens with the names and Bluetooth adresses available in your surroundings. When you click on the name you want to connact to BluetoothClient1 will connect to that device. The notifier will then show on your phone's screen wether the connectio was successfull or failed.



As the phone is now connected to the ESP32 the program just sits there waiting till you press the Led On or Led Off button.
When you press Button1 (Led On) the program checks wether Bluetooth is still connected and if so it sends the text "On\n" over Bluetooth to your phone. On is of course obvious. The "\n" after "On" will send a newline character. This makes any text displayed on the Serial Monitor on the ESP32 print the text and advances to a new line on the screen. It also allows us in the ESP32 program to check wether the complete text has been send.



Actually the code for the second button is the same as for the first. Only this time we send the text "Off\n"

And that is all.

Obviously you can expand this with as many buttons as you want and alter the texts that are send. I fancy vivid colors but adjust the colour settings to your own likings.

Now you can use the AI companion on your Phone to test the App or in Mit's App Inventor build the APK file and transfer that over USB to your phone.

If you do not have the time to build the app or start with App Inventor you can download the ready-to-use APK file here. Download it, transfer it to your phone and install it:

https://www.mediafire.com/file/gtcztpmompfbuwa/ESP32Bluetooth.apk/file

The ESP32 program.

The Arduino IDE provides us with the BluetoothSerial library. The Library automatically installed when the ESP32 board is installed.
There are some examples included but I am not going to use these as they only send 1 character. We are going to send words like in this example "On" and "Off". So I made my own program.

#include "BluetoothSerial.h"
#if !defined(CONFIG_BT_ENABLED) || !defined(CONFIG_BLUEDROID_ENABLED)
#error Bluetooth is not enabled! Please run `make menuconfig` to and enable it
#endif
String Charrcvd;
String text;
BluetoothSerial SerialBT;
void setup() 
{
 Serial.begin(115200);
 SerialBT.begin("ESP32BTtest"); //Bluetooth device name
 Serial.println("Bluetooth started, now pair your phone");
 pinMode(5, OUTPUT);
}
void loop() 
{
 if (SerialBT.available()) 
 {
 Charrcvd = SerialBT.readString();
 {
 text = text + Charrcvd;
 }
 }
 if (text != "")
 {
 Serial.println(text.substring(0,text.length()-1));
 Serial.println(text.length());
 if (text.substring(0,text.length()-1)== "On") 
 {
 Serial.println("Received: On");
 digitalWrite(5, HIGH);
 }
 if (text.substring(0,text.length()-1)== "Off") 
 {
 Serial.println("Received: Off");
 digitalWrite(5, LOW);
 }
 text = "";
 delay(20);
 }
}

As usual in my tutorials I'll explain the parts of the program.

#include "BluetoothSerial.h"

#if !defined(CONFIG_BT_ENABLED) || !defined(CONFIG_BLUEDROID_ENABLED)
#error Bluetooth is not enabled! Please run `make menuconfig` to and enable it
#endif

String Charrcvd;
String text;

BluetoothSerial SerialBT;

void setup()
{
 Serial.begin(115200);
 SerialBT.begin("ESP32BTtest"); //Bluetooth device name
 Serial.println("Bluetooth started, now pair your phone");
 pinMode(5, OUTPUT);
}

 if (SerialBT.available())
 {
 Charrcvd = SerialBT.readString();
 {
 text = text + Charrcvd;
 }
 }

 if (text != "")
 {
 Serial.println(text.substring(0,text.length()-1));
 Serial.println(text.length());

 if (text.substring(0,text.length()-1)== "On")
 {
 Serial.println("Received: On");
 digitalWrite(5, HIGH);
 }

 if (text.substring(0,text.length()-1)== "Off")
 {
 Serial.println("Received: Off");
 digitalWrite(5, LOW);
 }

 text = "";
 delay(20);