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Basics: Project 072e

Project name: ESP32 Development board - logging temperature to MicroSD Card/SD card

Tags: Arduino, ESP32 Dev Module, ESP32 development board, ESP32 Development board with WiFi and Bluetooth, ESP32-DevKitC V4 development board, ESP-WROOM-32 module with ESP32‑D0WDQ6 chip, Espressif Systems, ESP32-based development board, ESP32 modules, ESP32-WROOM-32, ESP32-WROOM-32U, ESP32-WROOM-32D, ESP32-SOLO-1, USB-UART bridge, IOT, ESP-WROOM-32 Dev Module, ESP32 DEVKITV1, Installing the ESP32 Board in Arduino IDE, Uploading sketch, logging temperature to MicroSD Card, data logging, SD Card or Micro SD Card Module

Attachments: library1, library2, library3, sketch2

In this project, you need these parts :

1. ESP32 development board with WiFi and Bluetooth and USB A / micro USB B cable 1 pc

2.Jumper cables F-F, M-M, F-M

3.Micro SD card with adapter 1 pc

4. SD card module 1 pc

5. DS18B20 one wire digital temperature sensor waterproof or not 1 pc

6. Resistor 1 pc (4.7KOhm (you can use similar values))

7. Breadboard 1 pc

General

We will learn how to log data with timestamps to a microSD card using ESP32 development board. 

There are a lot of different development boards made. You can find more information about them here. 

Project steps:

1. The ESP32 development board reads temperature using the DS18B20 temperature sensor.
2. ESP32 development board needs a Wi-Fi connection as after getting the reading, it makes a request to an NTP (Network Time Protocol) server to get date and time. 
3. The data (temperature and timestamp) are logged to a microSD card. We are using a SD card module to log temperature.
4. ESP32 development board sleeps for 10 minutes.
5. ESP32 development board wakes up and repeats the process.

Understanding the SD card module

You can read more about it here.

Understanding the ESP32 Development board with WiFi and Bluetooth

We will discuss here an Espressif Systems products. Our development board is using ESP-WROOM-32 module from Espressif Systems.

Espressif offers a wide range of fully-certified Wi-Fi & BT modules powered by their own advanced SoCs.

1. Dual-core Modules with Wi-Fi & Dual-mode Bluetooth

Features

• Two independently-controlled CPU cores with adjustable clock frequency, ranging from 80 MHz to 240 MHz
• +19.5 dBm output at the antenna ensures a good physical range
• Classic Bluetooth for legacy connections, also supporting L2CAP, SDP, GAP, SMP, AVDTP, AVCTP, A2DP (SNK) and AVRCP (CT)
• Support for Bluetooth Low Energy (BLE) profiles including L2CAP, GAP, GATT, SMP, and GATT-based profiles like BluFi, SPP-like, etc
• Bluetooth Low Energy (BLE) connects to smart phones, broadcasting low-energy beacons for easy detection
• Sleep current is less than 5 μA, making it suitable for battery-powered and wearable-electronics applications
• Integrates 4 MB flash
• Peripherals include capacitive touch sensors, Hall sensor, low-noise sense amplifiers, SD card interface, Ethernet, high-speed SPI, UART, I2S and I2C
• Fully certified with integrated antenna and software stacks

2. Single-core Modules with Wi-Fi & Dual-mode Bluetooth

Features

• High-performance 160 MHz single-core CPU
• +19.5 dBm output at the antenna ensures a good physical range
• Classic Bluetooth for legacy connections, also supporting L2CAP, SDP, GAP, SMP, AVDTP, AVCTP, A2DP (SNK) and AVRCP (CT)
• Support for Bluetooth Low Energy (BLE) profiles including L2CAP, GAP, GATT, SMP, and GATT-based profiles like BluFi, SPP-like, etc
• Bluetooth Low Energy (BLE) connects to smart phones, broadcasting low-energy beacons for easy detection
• Sleep current is less than 5 μA, making it suitable for battery-powered and wearable-electronics applications
• Peripherals include capacitive touch sensors, Hall sensor, low-noise sense amplifiers, SD card interface, Ethernet, high-speed SPI, UART, I2S and I2C
• Fully certified with integrated antenna and software stacks

3. Single-core Modules with 802.11b/g/n 2.4 GHz Wi-Fi

Features

• High-performance 160 MHz single-core CPU
• +19.5 dBm output at the antenna ensures a good physical range
• Sleep current is less than 20 μA, making it suitable for battery-powered and wearable-electronics applications
• Peripherals include UART, GPIO, I2C, I2S, SDIO, PWM, ADC and SPI
• Fully certified with integrated antenna and software stacks

There are different development Boards made by Espressif Systems and other manufacturers. We will publish some information about Espressif Systems boards but you can also find out more information about other development boards here.

1. 2.4 GHz Wi-Fi & BT/BLE Development Boards

Features

• PC connectivity: USB
• Power supply options: USB (by default), or 5V/GND header pins, or 3V3/GND header pins
• SDK: ESP-IDF source code and example applications

2. 2.4 GHz Wi-Fi Development Boards

Features

• PC connectivity: USB
• SDK: ESP8266 SDK source code and example applications

3. 2.4 GHz Wi-Fi + BT/BLE + Sensor Development Boards

Features

• PC connectivity: USB
• SDK: ESP-IOT-SOLUTION source code and example applications

You can find more information (datasheets, schematics, pins descriptions, functional desgn descriptions) about each board by pressing Getting started link close to each board here.

ESP32 chip

ESP32 is a series of low cost, low power system on a chip microcontrollers with integrated Wi-Fi and dual-mode Bluetooth. The ESP32 series employs a Tensilica Xtensa LX6 microprocessor in both dual-core and single-core variations and includes in-built antenna switches, RF balun, power amplifier, low-noise receive amplifier, filters, and power management modules. ESP32 is created and developed by Espressif Systems, a Shanghai-based Chinese company, and is manufactured by TSMC using their 40 nm process. It is a successor to the ESP8266 microcontroller.

ESP32 can perform as a complete standalone system or as a slave device to a host MCU, reducing communication stack overhead on the main application processor. ESP32 can interface with other systems to provide Wi-Fi and Bluetooth functionality through its SPI / SDIO or I2C / UART interfaces.

ESP32 is highly-integrated with in-built antenna switches, RF balun, power amplifier, low-noise receive amplifier, filters, and power management modules. ESP32 adds priceless functionality and versatility to your applications with minimal Printed Circuit Board (PCB) requirements.

ESP32 is capable of functioning reliably in industrial environments, with an operating temperature ranging from –40°C to +125°C. Powered by advanced calibration circuitries, ESP32 can dynamically remove external circuit imperfections and adapt to changes in external conditions.

Engineered for mobile devices, wearable electronics and IoT applications, ESP32 achieves ultra-low power consumption with a combination of several types of proprietary software. ESP32 also includes state-of-the-art features, such as fine-grained clock gating, various power modes and dynamic power scaling.

Functional Block Diagram:

Features of the ESP32 include the following:

Processors:

• CPU: Xtensa dual-core (or single-core) 32-bit LX6 microprocessor, operating at 160 or 240 MHz and performing at up to 600 DMIPS
• Ultra low power (ULP) co-processor
• Memory: 520 KiB SRAM

Wireless connectivity:

• Wi-Fi: 802.11 b/g/n
• Bluetooth: v4.2 BR/EDR and BLE

Peripheral interfaces:

• 12-bit SAR ADC up to 18 channels
• 2 × 8-bit DACs
• 10 × touch sensors (capacitive sensing GPIOs)
• Temperature sensor
• 4 × SPI
• 2 × I²S interfaces
• 2 × I²C interfaces
• 3 × UART
• SD/SDIO/CE-ATA/MMC/eMMC host controller
• SDIO/SPI slave controller
• Ethernet MAC interface with dedicated DMA and IEEE 1588 Precision Time Protocol support
• CAN bus 2.0
• Infrared remote controller (TX/RX, up to 8 channels)
• Motor PWM
• LED PWM (up to 16 channels)
• Hall effect sensor
• Ultra low power analog pre-amplifier

Security:

• IEEE 802.11 standard security features all supported, including WFA, WPA/WPA2 and WAPI
• Secure boot
• Flash encryption
• 1024-bit OTP, up to 768-bit for customers
• Cryptographic hardware acceleration: AES, SHA-2, RSA, elliptic curve cryptography (ECC), random number generator (RNG)

Power management:

• Internal low-dropout regulator
• Individual power domain for RTC
• 5uA deep sleep current
• Wake up from GPIO interrupt, timer, ADC measurements, capacitive touch sensor interrupt

You can find ESP32 chip datasheet here, hardware design here, technical reference manual here.

Signals and connections of the SD card module

Note: depending on the module you’re using, the pins may be in a different order.

VCC (5V)  - connect to 5V pin Arduino Uno. If it is just VCC pin and no 3V3 pin connect VCC to 3.3V pin of Arduino Board

3V3 (or 3.3V) - connect to 3.3V pin Arduino Uno

CS (or SS or D3) (Chip Select or Slave Select) - the pin on each device that the master can use to enable and disable specific devices

MOSI (or DI or SI or CMD) (Master Out Slave In) - The Master line for sending data to the peripherals

CLK (or SCK) (Serial Clock) - The clock pulses which synchronize data transmission generated by the master

MISO (or DO or SO) (Master In Slave Out) - The Slave line for sending data to the master

GND (or G) - ground

CD - this is the Card Detect pin. It shorts to ground when a card is inserted. You should connect a pull up resistor (10K or so) and wire this to another pin if you want to detect when a card is inserted. 

Signals and connections of the ESP32 Development board with WiFi and Bluetooth

You can find more information (datasheets, schematics, pins descriptions, functional desgn descriptions) about each board (made by Espresiff Systems) by pressing Getting started link close to each board here.

Let's check our development board - ESP32 DEVKITV1 with ESP-WROOM-32 module from Espressif Systems:

Pinout diagram for the ESP Wroom 32 breakout:

ESP32-WROOM-32 - ESP32-WROOM-32 module soldered to the development board. Optionally ESP32-WROOM-32D, ESP32-WROOM-32U or ESP32-SOLO-1 module may be soldered instead of the ESP32-WROOM-32.

USB-UART Bridge - A single chip USB-UART bridge provides up to 3 Mbps transfers rates.

BOOT button - Download button: holding down the Boot button and pressing the EN button initiates the firmware download mode. Then user can download firmware through the serial port.

EN button - Reset button: pressing this button resets the system.

Micro USB Port - USB interface. It functions as the power supply for the board and the communication interface between PC and the ESP module.

TX0, TX2 - transmit pin. GPIO pin

RX0, RX2  - receive pin.  GPIO pin

3V3 (or 3V or 3.3V) - power supply pin (3-3.6V). 

GND - ground pin.

EN - Chip enable. Keep it on high (3.3V) for normal operation.

Vin - External power supply 5VDC.

Wiring

Step by Step instruction

The ESP32 is currently being integrated with the Arduino IDE like it was done for the ESP8266. There’s an add-on for the Arduino IDE that allows you to program the ESP32 using the Arduino IDE and its programming language.

1. Download and install the latest Arduino IDE Windows Installer from arduino.cc
2. Download and install Git and Git GUI from git-scm.com
3. Search for Git GUI, right-click the icon and select “Run as administrator“
4. 
5. Select the Clone Existing Repository option.
6. 
7. Select source and destination. Source Location: https://github.com/espressif/arduino-esp32.git
8. Target Directory:C:/Users/[YOUR_USER_NAME]/Documents/Arduino/hardware/espressif/esp32
9. Do not create the espressif/esp32 folders, because they will be created automatically.
10. 
11. Click Clone to start cloning the repository.Wait a few seconds while the repository is being cloned.
12. 
13. 
14. Open the folder: C:/Users/[YOUR_USER_NAME]/Documents/Arduino/hardware/espressif/esp32/tools
15. Right-click the get.exe file and select “Run as administrator“.
16. 
17. You will see that necessary files will be downloaded and upzipped. It will take some time.
18. 
19. When get.exe finishes, you should see the following files in the directory.
20. 
21. Plug the ESP32 development board to your PC and wait for the drivers to install (or install manually any that might be required).
22. Open Arduino IDE. 
23. Open Boards manager. Go to Tools -> Board -> Boards Manager… (in our case it’s the DOIT ESP32 DEVKIT V1)
24. Select COM port that the board is attached to (if you don’t see the COM Port in your Arduino IDE, you need to install the ESP32 CP210x USB to UART Bridge VCP Drivers)
25. 
26. Most SD cards work right out of the box, but it's possible you have one that was used in a computer or camera and it cannot be read by the SD library. Formatting the card will create a file system that the Arduino can read and write to. It's not desirable to format SD cards frequently, as it shortens their life span. You’ll need a SD reader and computer to format your card. The library supports the FAT16 and FAT32 filesystems, but use FAT16 when possible. See additional info here.
27. Format the SD card as FAT16 or FAT32. Insert the SD card in your computer. Go to My Computer and right click on the SD card. Select Format...  
28. A new window pops up. Select FAT32, press Start to initialize the formatting process and follow the onscreen instructions.
29. Insert the formatted SD card / MicroSD card with SD card adapter in the SD card module.
30. Connect the SD card module to the ESP32 development board. 
31. Modify sketch2 - replace SSID and password with your data.
32. Verify and upload the sketch2 to your ESP32 development board.
33. Open serial monitor at 115200 bps.
34. Press the ESP32 Enable button, and check that everything is working properly (the ESP32 is connected to your local network, and the microSD card is properly attached).
    Press the ESP32 development board EN button, and check that everything is working properly (the ESP32 development board connected to your local network, and the microSD card is properly attached).
35. 
36. Let this project run for a few hours to gather a decent amount of data, and when you’re happy with the data logging period, shut down the ESP32 development board and remove the SD from the SD card module.
37. Insert the SD card to a SD card reader connected to your computer (PC), open it, and you should have a data.txt file with the collected data.
38. 
39. You can open the data with a text editor, or use a spreadsheet to analyse and process your data. You can build charts to analyse the data with MS Excel or Google Sheets.

Code

The ESP32 development board is in deep sleep mode between each reading. In deep sleep mode, all your code should go in the setup() function, because the ESP32 development board never reaches the loop().

We use a conversion factor from microseconds to seconds, so you can set the sleep time in the TIME_TO_SLEEP variable in seconds. In this project, we force the ESP32 to go to sleep for 10 minutes (600 seconds). 

You need to enter your local network SSID and password in order to connect to it with your ESP32 development board.

You can use the setTimeOffset() method to adjust the time for your timezone: timeClient.setTimeOffset(3600);

To make the code easier to understand, the following functions made:

• getReadings(): reads the temperature from the DS18B20 temperature sensor;
• getTimeStamp(): gets date and time from the NTP server;
• logSDcard(): logs the preceding data to the microSD card.

writeFile() and appendFile() functions are used to write and append data to the microSD card.

Summary

We have learnt how to log data with timestamps to a microSD card using ESP32 development board.

Libraries:

• All libraries attached on the begining of the project description.
• SPI library included in your Arduino IDE.
• WiFi library included in your Arduino IDE.
• Dallas Temperature Control library. Download, unzip  and add to libraries in our PC, for example C:\Users\toshiba\Documents\Arduino\libraries. This link you can find in Preferences of Adruino IDE program which installed in your PC. You can read more about it here.
• One wire library. Download, unzip  and add to libraries in our PC, for example C:\Users\toshiba\Documents\Arduino\libraries. This link you can find in Preferences of Adruino IDE program which installed in your PC. You can read more about it here.
• NTPClient library. Download, unzip  and add to libraries in our PC, for example C:\Users\toshiba\Documents\Arduino\libraries. This link you can find in Preferences of Adruino IDE program which installed in your PC. You can read more about it here.

Sketch:

• See attachment on the begining of this project