Category Archives: Arduino Tutorials

“error: cannot access /dev/ttyUSB0” Arduino (NodeMCU) esp8266

Question: Getting permission “error: cannot access /dev/ttyUSB0”
Answer: Just open terminal (Ctrl+Alt+T) and type this command and enter root password
$ sudo usermod -a -G dialout ${USER}

On Linux (Ubuntu), Arduino IDE will not be able to upload sketches (or communicate with the board at all) if you don’t change permissions on /dev/ttyUSB0 appropriately. Same as with the NodeMCU ESPlorer IDE, etc. Actually, this very problem comes up whenever you want to access a (virtual) Serial COM port on Linux.

It might happen that when you upload a sketch – after you have selected your board and serial port -, you get an error Error opening serial port … If you get this error, you need to set serial port permission.

Open Terminal and type:

$ ls -l /dev/ttyUSB*

you will get something like:

crw-rw---- 1 root dialout 188, 0 5 apr 23.01 ttyUSB0

The “0” at the end of USB might be a different number, or multiple entries might be returned. The data we need is “dialout” (is the group owner of the file).

Now we just need to add our user to the group:

$ sudo usermod -a -G dialout ${USER}

NOTE: where USER is NOT  your linux user name keep as it is.

In some cases, You will need to log out and log in again for this change to take effect.

How to convert integer to string and string to int on Arduino ?

New version of arduino supports String data type . In this tutorial we will see both integer to string and string to integer conversion. Conversion of integer to string can be done using single line statement.

Example:
int a = 1234;
String myStr;
myStr = String(a);  //Converts integer to string

Continue reading How to convert integer to string and string to int on Arduino ?

Tutorial On Arduino Watchdog Timer Setup

Today in this tutorial we will learn importance of watchdog timer and configuring watchdog timer in Arduino.

What is Watchdog Timer ?

A watchdog timer (WDT) is a hardware timer that automatically generates a system reset if the main program neglects to periodically service(reset) it. The Watchdog Timer is clocked from a separate On-chip Oscillator which runs at 1 MHz. This is the typical value at V CC = 5V. It is often used to automatically reset an Arduino that hangs because of a software or hardware fault. Some systems may also refer to it as a computer operating properly (COP) timer. All Arduino boards have watchdog timer hardware. Continue reading Tutorial On Arduino Watchdog Timer Setup

Arduino relay module interface

The new KEYES 5V Relay Module is perfectly made for Arduino application. It has three pins, the VCC, GND and Signal. It can act as switch if the circuit and the load circuit have different supply voltage. It is commonly use if the load circuit is AC. It is a switch used to connect isolated connection from the circuit using a circuit signal. It has red LED that turns on every time the coil is energized or the signal pin has a high input. Commonly used in automation control circuit, it is actually a small Current to control a large current operation “automatic switch.”

Arduino Connection with Relay Module

Arduino Relay Module Interface

For the DC part of the circuit:

Arduino digital pin 10 –> module pin S
Arduino GND –> module pin –
Arduino +5V –> module pin +

AC Part of the circuit:

On the AC side connect your feed to Common (middle contact) and use NO (Normally Open) to Lamp. It will get power when (S) is high.

Warning: Always be very careful when experimenting with AC, electrical shock can result in serious injures.

Relay module from bottom side is open when AC is connected do not touch the circuit.

Arduino Program for Relay module

This program will turn on and off the Lamp. Similar to Blink example. You can see module led also blinks.