ESP32 with multiple DS18B20 temperature sensors


Guide to ESP32 with multiple DS18B20 temperature sensors from Random Nerd Tutorials:

This guide shows how to read temperature from multiple DS18B20 temperature sensors with the ESP32 using Arduino IDE. We’ll show you how to wire the sensors on the same data bus to the ESP32, install the needed libraries, and a sketch example you can use in your own projects. This tutorial is also compatible with the ESP8266 and the Arduino boards.

EEPROM rotation for ESP8266 and ESP32


Xose Pérez over at Tinkerman writes:

The Arduino Core for ESP8266 and ESP32 uses one SPI flash memory sector to emulate an EEPROM. When you initialize the EEPROM object (calling begin) it reads the contents of the sector into a memory buffer. Reading a writing is done over that in-memory buffer. Whenever you call commit it write the contents back to the flash sector.
Due to the nature of this flash memory (NOR) a full sector erase must be done prior to write any new data. If a power failure (intended or not) happens during this process the sector data is lost.
Also, writing data to a NOR memory can be done byte by byte but only to change a 1 to a 0. The only way to turn 0s to 1s is to perform a sector erase which turns all memory positions in that sector to 1. But sector erasing must be done in full sectors, thus wearing out the flash memory faster.

How can we overcome these problems?

Full details at

The smallest esp32 module (so far…)

Some months ago, Espressif announced the production of a new chip, named ESP32-PICO-D4.


It’s a complete SiP (System in Package), that is a chip which integrates the esp32 microcontroller, a 4Mbit flash memory, a crystal oscillator, filter capacitors and RF matching links. The chip datasheet is available on the official website.

Using this chip, it’s possible to create very small modules. I recently received one of those from Aliexpress:



To better understand how small it is, let’s compare its size with a “classic” ESP-WROOM-32 module and with a 1 euro coin:


The module includes a chip antenna; it’s also possible to connect an external antenna thanks to the presence of an I-PEX connector.

In conclusion, the availability of the ESP32-PICO-D4 SiP makes it possible to use the esp32 chip in applications where the available space is very small…

ESP32, PlatformIO

PlatformIO is an opensource ecosystem (as it’s defined in the homepage of the project) to develop IoT projects.

The heart of the platform is a software component named PlatformIO Core. This component includes:

  • a cross-platform compiler
  • a libraries and dependences manager
  • a serial monitor

PlatformIO Core is developed in Python and therefore it can run on different operating systems (Windows, Linux, MacOS).

Although you can use the Core component directly, PlatformIO’s strength lies in its IDE, which allows the development of multi-platform projects and integrates with the Core itself.

In this article I’m going to show you how to use PlatformIO to develop projects running on the esp32 chip.


PlatformIO IDE is provided as a plugin for two different development tools: Atom and VisualStudio Code. I tried both solutions and I preferred VSCode: both the installation and the use are simpler and more immediate.

Install VSCode after having downloaded the package from Microsoft’s website (the installer is available for Windows, Linux and MacOS).

Open the Package Manager:


search the PlatformIO IDE package, then click on Install:


wait until the installation is complete:


Hello world

Now it’s time to develop your first program, which traditionally will display the sentence Hello world! on the terminal.

If it doesn’t show up automatically, open the PlatformIO’s homepage:


then click on New Project:


give a name to the project and choose a devboard based on the esp32 chip (in this example I’ll use a Lolin32 board by Wemos). PlatformIO supports both the esp-idf framework and the arduino-esp32 one. All my tutorials are based on the first one:


PlatformIO automatically creates some folders for your project. Choose the src folder (it stands for source, that is the folder which will contain the source code) and create a new file:


name the file main.c and type the simple program as it follows:


run the compiler by clicking on the corresponding button in the bottom bar:


the editor displays an error… indeed your code is using the printf() function without having included the library:


add the missing line, now you should be able to complile the code without errors:


PlatformIO can also upload the compiled program to your board. Thanks to its auto-detect feature, you usually don’t need to specify the serial port the board is connected to:


Serial monitor

PlatformIO also includes a serial monitor you can use to test your program. By default, this monitor connects to the serial port with a speed of 9600 baud. The esp32 chip instead has a default speed of 115200 baud; you have therefore to change the platformio.ini file included in your folder as it follows:


Now open the serial monitor; you should see the correct output of your program:



I found the use of PlatformIO really immediate: after a few minutes I was able to develop, compile, load and test a program. Try it and leave a comment with your impressions!


ESP32 (35) – BLE, scan response

In the previous posts I explained how to receive and send advertising packets based on the Bluetooth LE standard.

The payload (that is the amount of “useful” data) of those packets is at most 31 bytes. It isn’t much: if – for example – you want to include the device name, little place remains for other data.

The BLE standard allows peripherals to send additional data using the scan request – scan response process.

When a device receives an advertising packet, it can contact the transmitter by sending a scan request packet to request further information. When receiving a scan request package, the peripheral can respond with a scan response packet:


Advertising and scan request packets have the same format; it’s therefore possible to transfer, using scan response, additional 31 bytes of data.


The esp framework offers two modes for configuring the content of a scan response packet: using the esp_ble_adv_data_t struct or creating a byte array (raw mode). These modes are similar to the ones used to configure advertising packets you learned in previous articles (struct and raw mode).

In the first case, you have to declare a second struct, in addition to the one related to the advertising packet, to define the content of the scan response packet:

static uint8_t manufacturer_data[6] = {0xE5,0x02,0x01,0x01,0x01,0x01};
static esp_ble_adv_data_t scan_rsp_data = {
  .set_scan_rsp = true,
  .manufacturer_len = 6,
  .p_manufacturer_data = manufacturer_data,

Very important is set to true the set_scan_rsp parameter. It’s indeed this parameter what tells the driver that this struct is related to the scan response packet.

You can then pass the new struct to the driver, with the same function used previously:


The driver will call the callback function twice: one to indicate the successful configuration of the advertising packet and one for the configuration of the scan response one. The two events are different:


You have to wait until both the events have triggered before starting the advertising process. In my example program (you can download the source code from my Github repository) I use two boolean variables:

bool adv_data_set = false;
bool scan_rsp_data_set = false;
  adv_data_set = true;
  if(scan_rsp_data_set) esp_ble_gap_start_advertising(&ble_adv_params); break;
  scan_rsp_data_set = true;
  if(adv_data_set) esp_ble_gap_start_advertising(&ble_adv_params); break;

If you want to use the raw mode instead, you have to declare a byte array and fill it with the content of the payload of the packet. Then you can use a specific function of the framework to pass the array to the driver:

static uint8_t scan_rsp_raw_data[8] = {0x07,0xFF,0xE5,0x02,0x01,0x01,0x01,0x01};
esp_ble_gap_config_scan_rsp_data_raw(scan_rsp_raw_data, 8);

did you notice that the content of the scan response packet is the same in the two examples?

The driver will confirm the configuration of the packet with a dedicated event. Also in this case you have to wait for the end of both configurations (advertising and scan response):

  scan_rsp_data_set = true;
  if(adv_data_set) esp_ble_gap_start_advertising(&ble_adv_params); break;
You can also mix the two modes in your program. For example you can configure the advertising packet using the struct and configure the scan response one using the raw mode.

Now with the nRF Connect app you can verify that your scan response packet is correctly received by your smartphone:


In the following video I explain how I built the payload of the packet and how the program works:

ESP32 (34) – BLE, raw advertising

In the previous post, you learned how to send BLE advertising packets with the esp32 chip.

To define the content of the packet, you used a struct, of the esp_ble_adv_data_t type:


The struct’s definition is included in the esp_gap_ble_api.h file:


Although there are many fields available, sometimes it is necessary to be able to define the content of the advertising packet arbitrarily. For this reason, the esp-idf framework provides a raw mode.

Instead of defining a struct, you create a byte array and fill it with the entire contents of the packet’s payload:

static uint8_t adv_raw_data[10] = 

then you can use the esp_ble_gap_config_scan_rsp_data_raw() function to pass the array to the driver. You have to specify both the array and its size as parameters:

esp_ble_gap_config_scan_rsp_data_raw(scan_rsp_raw_data, 8);

When using this new function, it also changes the event that the driver passes to your callback function when the configuration is complete. The new event is ESP_GAP_BLE_ADV_DATA_RAW_SET_COMPLETE_EVT. As in the previous example, when this event is triggered you can start the advertising process:


Raw data

For the advertising process to work, the data contained in the array must correspond to a valid payload.

In the blog post about the iBeacons, I’ve already shown you its structure. Let’s briefly review it:


The payload contains one or more AD (advertising data) structures. Each structure is made by 3 fields:

  • an initial byte that represents the length (in bytes) of the structure, excluding itself
  • a byte that represents the type of the data contained in the structure
  • a variable number of bytes which are the actual data

The codes that can be used to define the type of data can be found in the Bluetooth specifications. Depending on the type of data, it is then necessary to apply a particular format to the data that follows. The necessary information is found in the Core Specification Supplement document (available on the website).

Let’s see a simple example: the ADType 0x09 represents the complete local name, which is the name of the device. This name must be specified in AD data with simply a sequence of the ASCII codes that correspond to the different letters.

You can use a website to do the conversion:


The payload to transmit this name is therefore:

adv_raw_data[7] = {0x06,0x09,0x4d,0x79,0x42,0x4c,0x45};

The first byte has value 0x06 that is the sum of the name length (5 bytes) and 1 byte for the data type (0x09).


In the following video you can see how I use the raw advertising feature to simulate the advertising packet of my iBeacon and therefore I’m able to activate the relay as in the previous example.

The source code of the program is available in my Github repository.

Alexa (Echo) with ESP32 and ESP8266 – Voice controlled relay


Rui Santos writes, “In this project, you’re going to learn how to control the ESP8266 or the ESP32 with voice commands using Alexa (Amazon Echo Dot). As an example, we’ll control two 12V lamps connected to a relay module. We’ll also add two 433 MHz RF wall panel switches to physically control the lamps.”

More info at

Check out the video after the break.

ESP32 (33) – BLE, advertising

In the previous posts you learned how to use the esp32 chip to receive and parse the advertising packets transmitted by BLE peripherals. As a practical example, I developed a program to detect the presence of a particular iBeacon and activate an output accordingly.

In today’s tutorial, you’ll learn how to transmit advertising packets instead.

Advertising process

You’ve already discovered that the Bluetooth driver included in the esp-idf stack is executed in a dedicated thread. Whenever the driver needs to send a notification to your program, it calls a callback function indicating which event has triggered.

The advertising process is very simple:

  • the program configures the data to be transmitted with esp_ble_gap_config_adv_data()
  • the driver reports that it has finished the configuration with the event ESP_GAP_BLE_ADV_DATA_SET_COMPLETE_EVT
  • the program can now start the advertising process with esp_ble_gap_start_advertising()
  • the driver reports that the process has started with the event ESP_GAP_BLE_ADV_START_COMPLETE_EVT


Advertising DATA

It’s possible to tell the driver which data to include in the advertising packet with the following command:

esp_err_t esp_ble_gap_config_adv_data(esp_ble_adv_data_t *adv_data);

The command accepts as parameter a pointer to an esp_ble_adv_data_t struct:


The meaning of the different fields is explained in the Supplement to the Bluetooth Core Specification document.

First let’s find out how to transmit the device name. You have to use the esp_ble_gap_set_device_name() function to pass the name to the driver and set the field include_name to true in the struct:

static esp_ble_adv_data_t adv_data = {
  .include_name = true,

Using the flags, you can publish some features of your device. The available constants are:


you can combine them with the OR operator. If, for example, you want to tell the world that your device is limited discoverable (i.e. it sends the advertising packets only for a limited time, usually 30 seconds) and that it doesn’t support classic Bluetooth (BR/EDR, Basic Rate/Enhanced Data Rate) you’ll write:

static esp_ble_adv_data_t adv_data = {

Advertising PARAMETERS

After configuring the content of the advertising packet, you have also to tell the driver how to send the packet.

The command:

esp_err_t esp_ble_gap_start_advertising(esp_ble_adv_params_t *adv_params);

accepts as parameter an esp_ble_adv_params_t struct:


You can configure the minimum and maximum transmission interval of the packet. The two parameters can assume a value from 0x20 to 0x4000. To calculate the interval in milliseconds, the value specified must be multiplied for 0.625. This means that the minimum value (0x20) corresponds to an interval of 12.5ms.

The esp_gap_ble_api.h file lists the constants that can be used for the other parameters (esp_ble_adv_type_t, esp_ble_addr_type_t …).

For example, let’s configure the advertising process as it follows:

  • minimum transmission interval: 0x20, maximum: 0x40
  • non connectable device (it doesn’t accept incoming connections and only sends data in broadcast)
  • public MAC address
  • transmission on all the 3 channels dedicated to advertising packets
  • no filter on devices who can perform a scan or connect
static esp_ble_adv_params_t ble_adv_params = {
  .adv_int_min = 0x20,
  .adv_int_max = 0x40,
  .adv_type = ADV_TYPE_NONCONN_IND,
  .own_addr_type  = BLE_ADDR_TYPE_PUBLIC,
  .channel_map = ADV_CHNL_ALL,
  .adv_filter_policy  = ADV_FILTER_ALLOW_SCAN_ANY_CON_ANY,


I prepared a program that includes what explained above. The source code is available in my Github repository.

Here’s how it works:

ESP32 (32) – BLE, iBeacon

In my previous article I explained the Bluetooth Low Energy technology and the advertising process.

You learned that a BLE device can leverage the advertising packets to send data; in this case the device is called broadcaster and the devices which receive data are called observers.

The payload of an advertising packet has the following structure:


ADV ADDR is the device MAC address (this is the address displayed by the program developed in the previous article) and ADV DATA is a field, with a max length of 31 bytes, that contains one or more structures, each with 3 elements:

  • AD length is the total length (in bytes) of each data structure
  • AD type is the type of data contained in the structure
  • AD data is the real data

The official website of the Bluetooth Special Interest Group lists all the available AD types.

A device, for example, can transmit its local name using the AD type 0x09:


In scan mode, the Bluetooth driver returns to the program the received data (ADV DATA) in the scan_result->scan_rst.ble_adv array. This array contains uint8_t values and it’s size is scan_result->scan_rst.adv_data_len.

The Bluedroid library contains a method, esp_ble_resolve_adv_data(), which allows to get the value for a specific AD type passing the raw data. The header file esp_gap_ble_api.h contains definitions for the most common AD types:


In my Github repository you can find an updated version of the scan program. Thanks to what explained above, now the program can also display – if available – the name of the device:



A particular family of broadcaster devices are the iBeacons. These devices have been designed by Apple to allow interaction with IOS devices (iPhone …) based on location awareness. Let’s make an example: an iPhone can “notice” that it is close to a particular iBeacon, associated with a room in a museum, and therefore offer the user a brief guide to the exhibited works.


iBeacon specifications are available on Apple’s developer portal. iBeacons work transmitting advertising packets with  specific payload (ADV DATA):


The first structure has AD type = flags (0x01). Each bit has a different meaning, usually iBeacons use 0x0A value for AD data.

The second structure has type = 0xFF, that is Manufacturer Specific Data. The Bluetooth standard allows the different manufacturers to use this ID to transmit custom data. The total data length is 25 bytes (0x1A – 0x01 that is the length of the AD type field).

Apple specifications further subdivide the AD data field in several elements:


The first field is the manufacturer/company; iBeacons normally use the code 0x004C, assigned to Apple Inc. The next two fields define the iBeacon type and have a fixed value (0x02 e 0x15). The UUID field, together with the Major and Minor ones (optional, they can have a value of 0) uniquely identifies each iBeacon.  (insieme con i campi Major e Minor (facoltativi, possono essere impostati a 0) identificano univocamente il singolo iBeacon. Finally, the TX power field contains a measurement, one meter away from the iBeacon, of the received power and is useful for  precisely estimate the distance between the phone and the iBeacon itself.


I developed a program for the esp32 chip which turns a relay on if it detects a specific iBeacon. Via menuconfig you can configure the UUID of the iBeacon which triggers the led, the pin the led is connected to and the timeout – in seconds – after which the program turns the led off if the iBeacon is not detected anymore. You can moreover set a power threshold to control the distance at which the iBeacon is detected.

To parse the received packet and get the UUID value, in my program I used the method described in this article (parsing using a struct).

The program verifies if the received packet (event ESP_GAP_SEARCH_INQ_RES_EVT) was sent by an iBeacon checking that the packet length is 30 bytes and that its header contains the values listed above:

// iBeacon fixed header
ibeacon_header_t ibeacon_fixed_header = {
  .flags = {0x02, 0x01, 0x06},
  .length = 0x1A,
  .type = 0xFF,
  .company_id = 0x004C,
  .beacon_type = 0x1502

It compares the fixed header with the received one using memcmp, function that compares two blocks in memory:

if(memcmp(adv_data, ibeacon_fixed_header, sizeof(ibeacon_fixed_header)))
  result = true;

The source program is available in my Github repository, here’s a video that shows how it works:

Game audio for the ESP32


ESP32 game audio at Buildlog.Net blog:

I have been working on some games for the ESP32 and needed some decent quality audio with a minimum number of additional components.  I was bouncing between using the DAC and using the I2S bus. The DAC requires less external parts, so I went that way. I ended up creating a very simple library for use in he Arduino IDE. (Note: This only works with ESP32)

Check out the video after the break.