Arduino

How to print 16-bit uint16_t as four hex digits in Arduino

When using Arduino, you often want to print the hex value of a 16-bit value such as a uint16_t, consisting of four hex digits. For example, if you have uint16_t val = 2022;, you intend to print 07E6.

In Arduino you can do that using Serial.printf() with %04x as format specifier.

Furthermore, you typically want to invert the byte order of the uint16_t using __builtin_bswap16()since it’s more inuitive to write the hex value MSB-first (big-endian) while most hardware platforms represent the uint16_t as LSB-first (little-endian):

Serial.printf("val = %04x\r\n", __builtin_bswap16(val));

When using printf, %x means to format the value as hex. 04 means to pad the value with 0s up to a length of 4 digits. If you would format 2022 using just %x, it would print 7E6  instead of 07E5. This is why you need to use %04x instead.

Posted by Uli Köhler in Arduino, Electronics, Embedded, PlatformIO

How to print byte as two hex digits in Arduino

In embedded programming, you often want to print the hex value of a byte, consisting of two hex digits. For example, if you have uint8_t val = 14;, you intend to print 0x0E.

In Arduino you can do that using Serial.printf() with %02x as format specifier:

Serial.printf("val = %02x\r\n", val);

When using printf, %x means to format the value as hex. 02 means to pad the value with 0s up to a length of 2 digits. If you would format 14 using just %x, it would print E  instead of 0E. This is why you need to use %02x.

Posted by Uli Köhler in Arduino, Electronics, Embedded, PlatformIO

Arduino I2C: Wire.endTransmission() before or after Wire.requestFrom() ?

The correct order to call Wire commands in Arduino is:

Wire.beginTransmission(MY_I2C_ADDR);
Wire.write(addr);
Wire.endTransmission();
Wire.requestFrom(MY_I2C_ADDR, 1); // Request one byte
delay(5); // Wait for data to be available
uint8_t value = Wire.read();

So you call Wire.endTransmission() after Wire.write() and call Wire.requestFrom() directly after Wire.endTransmission()

Posted by Uli Köhler in Arduino, Electronics, Embedded, PlatformIO

How to set pin speed/alternate function in STM32 Arduino (PlatformIO)

You can use the STM32 HAL (STM32CubeMX) even when using Arduino as a framework for STM32 boards in PlatformIO:

GPIO_InitTypeDef pinInit = {
  .Pin = GPIO_PIN_8,
  .Mode = GPIO_MODE_AF_PP,
  .Pull = GPIO_NOPULL,
  .Speed = GPIO_SPEED_FREQ_VERY_HIGH,
  .Alternate = GPIO_AF1_TIM1
};
HAL_GPIO_Init(GPIOA, &pinInit);

Use

#include <stm32f4xx_hal_gpio.h>

in order to include the HAL functions.

Posted by Uli Köhler in Arduino, Electronics, PlatformIO, STM32

How I fixed PlatformIO Arduino

Problem:

When uploading an Atmel AVR firmware like for the Arduino Uno using PlatformIO, you see an error message like

Auto-detected: /dev/ttyACM0
Uploading .pio/build/uno/firmware.hex
avrdude: stk500_recv(): programmer is not responding
avrdude: stk500_getsync() attempt 1 of 10: not in sync: resp=0x00
avrdude: stk500_recv(): programmer is not responding
avrdude: stk500_getsync() attempt 2 of 10: not in sync: resp=0x00
avrdude: stk500_recv(): programmer is not responding
avrdude: stk500_getsync() attempt 3 of 10: not in sync: resp=0x00
avrdude: stk500_recv(): programmer is not responding
avrdude: stk500_getsync() attempt 4 of 10: not in sync: resp=0x00
avrdude: stk500_recv(): programmer is not responding
avrdude: stk500_getsync() attempt 5 of 10: not in sync: resp=0x00
avrdude: stk500_recv(): programmer is not responding
avrdude: stk500_getsync() attempt 6 of 10: not in sync: resp=0x00
avrdude: stk500_recv(): programmer is not responding
avrdude: stk500_getsync() attempt 7 of 10: not in sync: resp=0x00
avrdude: stk500_recv(): programmer is not responding
avrdude: stk500_getsync() attempt 8 of 10: not in sync: resp=0x00
avrdude: stk500_recv(): programmer is not responding
avrdude: stk500_getsync() attempt 9 of 10: not in sync: resp=0x00
avrdude: stk500_recv(): programmer is not responding
avrdude: stk500_getsync() attempt 10 of 10: not in sync: resp=0x00

avrdude done.  Thank you.

*** [upload] Error 1

or

Auto-detected: /dev/ttyUSB0
Uploading .pio/build/uno/firmware.hex
avrdude: stk500_getsync() attempt 1 of 10: not in sync: resp=0x00
avrdude: stk500_getsync() attempt 2 of 10: not in sync: resp=0x00
avrdude: stk500_getsync() attempt 3 of 10: not in sync: resp=0x00
avrdude: stk500_getsync() attempt 4 of 10: not in sync: resp=0x00
avrdude: stk500_getsync() attempt 5 of 10: not in sync: resp=0x00
avrdude: stk500_getsync() attempt 6 of 10: not in sync: resp=0x00
avrdude: stk500_getsync() attempt 7 of 10: not in sync: resp=0x00
avrdude: stk500_getsync() attempt 8 of 10: not in sync: resp=0x00
avrdude: stk500_getsync() attempt 9 of 10: not in sync: resp=0x00
avrdude: stk500_getsync() attempt 10 of 10: not in sync: resp=0x00

avrdude done.  Thank you.

*** [upload] Error 1

Solution

This issue occurs if:

  • Either there is no bootloader on the board or the bootloader is damaged or
  • The wrong upload speed for this bootloader is selected

Note that  you can flash a new/updated bootloader using the Arduino IDE, overwriting the old / defective bootloader. You can do that using an AVR programmer, or you can do it using another Arduino. This will make working with the board much easier in general, but it will most likely fix your programming issues. In case you flash a new bootloader, the correct upload_speed setting in platformio.ini will typically be upload_speed = 115200.

In case you want to work with the bootloader currently present on the board, you need to select the correct upload_speed setting.

Depending on the age of the bootloader on the board, it will typically have either 115200, 57600 or 19200 baud speed.

In order to fix the issue, edit platformio.ini and add

upload_speed = 115200

then restart the upload. In case this doesn’t work, try

upload_speed = 57600

and

upload_speed = 19200

Rarely, the following setting work:

upload_speed = 9600

or

upload_speed = 230400

In case none of these settings work at all, either you are facing a hardware defect or you need to flash a new bootloader onto the board. I recommend to always try to flash a bootloader first before throwing away the board.

Posted by Uli Köhler in Arduino, Electronics, Embedded, PlatformIO

How fast is analogRead() on the ESP8266?

An analogRead() call on the ESP8266 takes about 90-100 microseconds.

I tested this experimentally using a Wemos D1 Mini board, PlatformIO and this code:

uint32_t t0 = micros();
for (size_t i = 0; i < 1000; i++)
{
    analogRead(A0);
}
uint32_t t1 = micros();
Serial.print("1000 analogRead() calls took [us]: ");
Serial.println(t1-t0);

Output:

1000 analogRead() calls took [us]: 97168

Since 1000 analogRead() calls (including some overhead from the loop) took 97.168ms, one analogRead() call takes about 97.168us (+-0.02us).

Posted by Uli Köhler in Arduino, Electronics, ESP8266/ESP32, PlatformIO

How to fix PlatformIO ESP8266 ArduinoOTA error: stopAll is not a member of WiFiUDP

Problem:

When compiling your PlatformIO firmware, you see an error message like

/home/uli/.platformio/packages/framework-arduinoespressif8266/libraries/ArduinoOTA/ArduinoOTA.cpp: In member function 'void ArduinoOTAClass::_runUpdate()':
/home/uli/.platformio/packages/framework-arduinoespressif8266/libraries/ArduinoOTA/ArduinoOTA.cpp:268:12: error: 'stopAll' is not a member of 'WiFiUDP'
  268 |   WiFiUDP::stopAll();
      |            ^~~~~~~

Solution:

Remove WiFi from the lib_deps secton of your platform.ini. Before the fix:

lib_deps =
    ESP Async [email protected]
    [email protected]
    WiFi

After the fix:

lib_deps =
    ESP Async [email protected]
    [email protected]

Now check your source code and replace any

#include <WiFi.h>

by

#include <ESP8266WiFi.h>

in order to prevent the WiFi.h: No Such File or Directory  issue as outlined in How to fix PlatformIO ESP8266 WiFi.h: No Such File or Directory

Now you need to completely remove the .pio folder from your project directory in order to ensure a clean build:

rm -rf .pio

After that, recompile your firmware.

Posted by Uli Köhler in Arduino, Electronics, ESP8266/ESP32, PlatformIO

How to fix PlatformIO ESP8266 WiFi.h: No Such File or Directory

Problem:

When compiling your PlatformIO firmware, you see an error message like

src/main.cpp:2:10: fatal error: WiFi.h: No such file or directory

**************************************************************
* Looking for WiFi.h dependency? Check our library registry!
*
* CLI  > platformio lib search "header:WiFi.h"
* Web  > https://platformio.org/lib/search?query=header:WiFi.h
*
**************************************************************

    2 | #include <WiFi.h>

Solution:

Instead of

#include <WiFi.h>

use

#include <ESP8266WiFi.h>

Now delete the .pio folder from the project directory to ensure a clean build by using:

rm -rf .pio

In case that doesn’t help, see our article on how to fix this issue by adding the WiFi library to the dependencies: How to fix PlatformIO WiFi.h: No Such File or Directory

Posted by Uli Köhler in Arduino, Electronics, ESP8266/ESP32, PlatformIO

How to fix PlatformIO multiple definition of `WiFi’ error

Problem:

When compiling your PlatformIO firmware, you see an error message like

Linking .pio/build/d1_mini_lite/firmware.elf
/home/uli/.platformio/packages/toolchain-xtensa/bin/../lib/gcc/xtensa-lx106-elf/10.3.0/../../../../xtensa-lx106-elf/bin/ld: .pio/build/d1_mini_lite/libbc0/libWiFi.a(WiFi.cpp.o):(.bss.WiFi+0x0): multiple definition of `WiFi'; .pio/build/d1_mini_lite/libd39/libESP8266WiFi.a(ESP8266WiFi.cpp.o):(.bss.WiFi+0x0): first defined here
collect2: error: ld returned 1 exit status
*** [.pio/build/d1_mini_lite/firmware.elf] Error 1

Solution:

Move WiFi in the lib_deps section in platformio.ini to the top of the list. Before the fix:

lib_deps =
    ESP Async [email protected]
    [email protected]
    WiFi

After the fix:

lib_deps =
    WiFi
    ESP Async [email protected]
    [email protected]

Now you need to completely remove the .pio folder from your project directory:

rm -rf .pio

After that, recompile your firmware.

Complete platformio.ini example after fixing the issue:

[env:d1_mini_lite]
platform = espressif8266
board = d1_mini_lite
framework = arduino
monitor_speed = 115200
lib_deps =
    WiFi
    ESP Async [email protected]
    [email protected]

 

Posted by Uli Köhler in Arduino, Electronics, PlatformIO

How to fix PlatformIO WiFi.h: No Such File or Directory

Important note: On the ESP8266, this solution is not recommended. See How to fix PlatformIO ESP8266 WiFi.h: No Such File or Directory instead

Problem:

When compiling your PlatformIO firmware, you see an error message like

src/main.cpp:2:10: fatal error: WiFi.h: No such file or directory

**************************************************************
* Looking for WiFi.h dependency? Check our library registry!
*
* CLI  > platformio lib search "header:WiFi.h"
* Web  > https://platformio.org/lib/search?query=header:WiFi.h
*
**************************************************************

    2 | #include <WiFi.h>

Solution:

Add WiFi to the lib_deps in platformio.ini (create lib_deps if it is not present already):

lib_deps =
    WiFi

and then recompile.

Complete platformio.ini example:

[env:d1_mini_lite]
platform = espressif8266
board = d1_mini_lite
framework = arduino
monitor_speed = 115200
lib_deps =
    ESP Async [email protected]
    [email protected]
    WiFi

 

Posted by Uli Köhler in Arduino, Electronics, PlatformIO

How to fix PlatformIO SPI.h: No Such File or Directory

Problem:

When compiling your PlatformIO firmware, you see an error message like

In file included from .pio/libdeps/esp32dev/Adafruit BusIO/Adafruit_BusIO_Register.h:2:0,
                 from .pio/libdeps/esp32dev/Adafruit INA219/Adafruit_INA219.h:21,
                 from .pio/libdeps/esp32dev/Adafruit INA219/Adafruit_INA219.cpp:31:
.pio/libdeps/esp32dev/Adafruit BusIO/Adafruit_SPIDevice.h:6:17: fatal error: SPI.h: No such file or directory

*************************************************************
* Looking for SPI.h dependency? Check our library registry!
*
* CLI  > platformio lib search "header:SPI.h"
* Web  > https://platformio.org/lib/search?query=header:SPI.h
*
*************************************************************

Solution:

Add SPI to the lib_deps in platformio.ini, for example, before:

lib_deps =
    adafruit/Adafruit INA219 @ ^1.1.1

After:

lib_deps =
    adafruit/Adafruit INA219 @ ^1.1.1
    SPI

and then recompile.

Posted by Uli Köhler in Arduino, Electronics, PlatformIO

How to fix PlatformIO Adafruit_BusIO_Register.h: No Such File or Directory

Problem:

When compiling your PlatformIO firmware, you see an error message like

In file included from .pio/libdeps/esp32dev/Adafruit INA219/Adafruit_INA219.cpp:31:0:
.pio/libdeps/esp32dev/Adafruit INA219/Adafruit_INA219.h:21:37: fatal error: Adafruit_BusIO_Register.h: No such file or directory

*********************************************************************************
* Looking for Adafruit_BusIO_Register.h dependency? Check our library registry!
*
* CLI  > platformio lib search "header:Adafruit_BusIO_Register.h"
* Web  > https://platformio.org/lib/search?query=header:Adafruit_BusIO_Register.h
*
*********************************************************************************

Solution:

Add adafruit/Adafruit BusIO @ ^1.9.3 to the lib_deps in platformio.ini, for example, before:

lib_deps =
    adafruit/Adafruit INA219 @ ^1.1.1

After:

lib_deps =
    adafruit/Adafruit INA219 @ ^1.1.1
    adafruit/Adafruit BusIO @ ^1.9.3

and then recompile.

Posted by Uli Köhler in Arduino, Electronics, PlatformIO

How to fix PlatformIO Wire.h: No Such File or Directory

Problem:

When compiling your PlatformIO firmware, you see an error message like

In file included from .pio/libdeps/esp32dev/Adafruit INA219/Adafruit_INA219.cpp:31:0:
.pio/libdeps/esp32dev/Adafruit INA219/Adafruit_INA219.cpp:29:18: fatal error: Wire.h: No such file or directory

**************************************************************
* Looking for Wire.h dependency? Check our library registry!
*
* CLI  > platformio lib search "header:Wire.h"
* Web  > https://platformio.org/lib/search?query=header:Wire.h
*
**************************************************************

Solution:

Add Wire to the lib_deps in platformio.ini, for example, before:

lib_deps =
    adafruit/Adafruit INA219 @ ^1.1.1

After:

lib_deps =
    adafruit/Adafruit INA219 @ ^1.1.1
    Wire

and then recompile.

Posted by Uli Köhler in Arduino, Electronics, PlatformIO

What is the default PlatformIO / Arduino ESP32 TIMER_BASE_CLK?

On PlatformIO / Arduino, by default the TIMER_BASE_CLK is 80 MHz (the maximum frequency the ESP32 can run at).

If you want to verify this yourself, use this firmware:

#include <Arduino.h>

void setup() {
    Serial.begin(115200);
    Serial.println(getCpuFrequencyMhz());
}

void loop() {
}

 

Posted by Uli Köhler in Arduino, Electronics, Embedded, ESP8266/ESP32, PlatformIO

How to fix PlatformIO serial monitor scrambled output

Problem:

When using the Monitor function of platformIO, you see strange characters instead of strings being printed, for example:

)�
�␜ܠ��J��1��1!y��!���!��

Solution:

This issue almost always appears due to the Monitor function using the wrong UART speed. You can see from the log in our screenshot above:

--- Miniterm on /dev/ttyUSB0  9600,8,N,1 ---

that PlatformIO is using 9600 baud in this case – but your microcontroller is sending data at a faster speed (or, rarely at a slower speed).

Most firmwares using serial IO use 115200 baud, so that’s what I’d recommend to try first, but if that doesn’t work, look out for config options named baud rate or similar, or for lines of code like

Serial.begin(57600);

in the firmware.

In order to change the Monitor UART speed, open platformio.ini and add

monitor_speed = 115200

Full platformio.ini example for ESP32:

[env:esp32dev]
platform = espressif32
board = esp32dev
framework = arduino
monitor_speed = 115200

After that, restart the Monitor function.

Posted by Uli Köhler in Arduino, Electronics, Embedded, ESP8266/ESP32, PlatformIO, STM32

How to fix ESP32 not connecting to the Wifi network

If you use a program like our minimal ESP32 wifi example:

#include <Arduino.h>
#include <WiFi.h>

void setup() {
  Serial.begin(115200);
  WiFi.begin("MyWifiNetworkName", "MyWifiPassword");
  while (WiFi.status() != WL_CONNECTED) {
    Serial.println("Wifi connecting...");
    delay(500);
  }
  Serial.println("Wifi connected");
}
void loop() {
  // put your main code here, to run repeatedly:
}

and you just see a loop of

Wifi connecting...

messages, press the RESET button of your board (or unplug and re-plug its power to reset) and and try again. If you still see just Wifi connecting... messages after trying to reset 5 times, most likely your wifi credentials are wrong or the ESP32 can’t see your Wifi network!

Otherwise, if your ESP32 sometimes connects to the Wifi network almost immediately and sometimes it doesn’t seem to connect at all, use this code instead to automatically reset the ESP32 if it doesn’t connect within 5 seconds:

// Wait for wifi to be connected
uint32_t notConnectedCounter = 0;
while (WiFi.status() != WL_CONNECTED) {
    delay(100);
    Serial.println("Wifi connecting...");
    notConnectedCounter++;
    if(notConnectedCounter > 150) { // Reset board if not connected after 5s
        Serial.println("Resetting due to Wifi not connecting...");
        ESP.restart();
    }
}

Full example:

#include <Arduino.h>
#include <WiFi.h>

void setup() {
  Serial.begin(115200);
  WiFi.begin("MyWifiSSID", "MyWifiPassword");

  // Wait for wifi to be connected
  uint32_t notConnectedCounter = 0;
  while (WiFi.status() != WL_CONNECTED) {
      delay(100);
      Serial.println("Wifi connecting...");
      notConnectedCounter++;
      if(notConnectedCounter > 150) { // Reset board if not connected after 5s
          Serial.println("Resetting due to Wifi not connecting...");
          ESP.restart();
      }
  }
  Serial.print("Wifi connected, IP address: ");
  Serial.println(WiFi.localIP());
}

void loop() {
  // put your main code here, to run repeatedly:
}

Alternatively, use this function:

/**
 * Wait for WiFi connection, and, if not connected, reboot
 */
void waitForWiFiConnectOrReboot(bool printOnSerial=true) {
  uint32_t notConnectedCounter = 0;
  while (WiFi.status() != WL_CONNECTED) {
      delay(100);
      if(printOnSerial) {
        Serial.println("Wifi connecting...");
      }
      notConnectedCounter++;
      if(notConnectedCounter > 150) { // Reset board if not connected after 5s
          if(printOnSerial) {
            Serial.println("Resetting due to Wifi not connecting...");
          }
          ESP.restart();
      }
  }
  if(printOnSerial) {
    // Print wifi IP addess
    Serial.println("IP address: ");
    Serial.println(WiFi.localIP());
  }
}

 

Posted by Uli Köhler in Arduino, ESP8266/ESP32, PlatformIO

ESP32 minimal WiFi client example

This example shows how to connect your ESP32 to an existing Wifi network using the Arduino Framework:

#include <Arduino.h>
#include <WiFi.h>

void setup() {
  Serial.begin(115200);
  WiFi.begin("MyWifiNetworkName", "MyWifiPassword");
  while (WiFi.status() != WL_CONNECTED) {
    Serial.println("Wifi connecting...");
    delay(500);
  }
  Serial.println("Wifi connected");
}
void loop() {
  // put your main code here, to run repeatedly:
}

 

Posted by Uli Köhler in Arduino, ESP8266/ESP32, PlatformIO

How to fix ArduinoJson error: DynamicJsonBuffer is a class from ArduinoJson 5

When you see an error message like

Compiling .pio\build\d1_mini\src\main.cpp.o
src\main.cpp:22:11: error: DynamicJsonBuffer is a class from ArduinoJson 5. Please see arduinojson.org/upgrade to learn how to upgrade your program to ArduinoJson version 6
       DynamicJsonBuffer jsonBuffer;

in your PlatformIO or Arduino project using the ArduinoJson library, your code was written for an old version of ArduinoJson.

According to the official ArduinoJson 5 to ArduinoJson 6 migration guide, you need to use DynamicJsonDocument instead. Note that DynamicJsonDocument uses a slightly different API compared to DynamicJsonDocument, hence you might need to adjust more than just changing the class names. But as a first step, replace e.g.

DynamicJsonBuffer json;

by

DynamicJsonDocument json(1024);
Posted by Uli Köhler in Arduino, ESP8266/ESP32, PlatformIO