Domen Bukovac, Author at Bukovac.si

I ordered a small strobe light more than a month ago from china, but it wasn’t delivered in time, so I made one from a LED light I had at home.

First, I wired this LED light through a NPN transistor. It couldn’t be wired directly to Arduino because it requires higher current than Arduino can provide. I’ve also wired a 10K Potentiometer for tuning the frequency of blinking.

Resistor wired from pin 2 is 1K Ohm and the pulldown resistor connecting transistor to the ground is 10K Ohm.

Programming everything was as simple turning pin on and off with delays in between linked to potentiometer. At higher frequencies I noticed that light was actually lit longer than it was off so the effect wasn’t as good as I expected it to be.

I had to adjust the delay before light turns on again to be longer at higher frequencies, but stay about the same at higher. I drew a graph time on-time off to represent this and figured out I could shift and stretch function y = -1/x to form the same line. The results were much better then.

Here is the code for Arduino.

int potPin = 2;    // input pin for the potentiometer
int ledPin = 2;   // pin for the LED
int val = 0;      
int onTime = 0;
int offTime = 0;

void setup() {
  pinMode(ledPin, OUTPUT);  // declare the ledPin as an OUTPUT 
}

void loop() {
  val = analogRead(potPin); // read the value from the potentiometer (10k Ohm) (approximately between 0 and 1000)
  
  onTime = val;
  offTime = (-2000000 / (onTime + 1000)) + 2000;
  
  onTime = onTime / 4;    //
  offTime = offTime / 4; // Intervals longer than 250ms were not useful for application, also makes potentiometer less sensible, so I could fine tune desired frequencies.

  if (onTime > 12)  { //keeps light off if potentiometer set to min
    digitalWrite(ledPin, HIGH); }
  delay(onTime);                  // how long the LED stays On
  
  if (onTime < 250){ //keeps light on when potentiometer set to max
    digitalWrite(ledPin, LOW); }
  delay(offTime);                  // how long the LED stays Off
}

int potPin = 2; // input pin for the potentiometer

int ledPin = 2; // pin for the LED

int val = 0;

int onTime = 0;

int offTime = 0;

void setup() {

pinMode(ledPin, OUTPUT); // declare the ledPin as an OUTPUT

}

void loop() {

val = analogRead(potPin); // read the value from the potentiometer (10k Ohm) (approximately between 0 and 1000)

onTime = val;

offTime = (-2000000 / (onTime + 1000)) + 2000;

onTime = onTime / 4; //

offTime = offTime / 4; // Intervals longer than 250ms were not useful for application, also makes potentiometer less sensible, so I could fine tune desired frequencies.

if (onTime > 12) { //keeps light off if potentiometer set to min

digitalWrite(ledPin, HIGH); }

delay(onTime); // how long the LED stays On

if (onTime < 250){ //keeps light on when potentiometer set to max

digitalWrite(ledPin, LOW); }

delay(offTime); // how long the LED stays Off

}

A clip of the strobe light working.

Last year I made Room automation with Raspberry Pi and few Arduinos for switching lights and air conditioner on and off using my phone. It required lots of components for accomplishing a simple task. The reason was that Arduino itself cannot connect to wifi and NRF24L01+ module doesn’t support TCP/IP protocol, so I needed Raspberry Pi for wifi connection. Also using new Raspberry Pi for each light switch is just too expensive. This time I used WeMos ESP8266.

ESP866 is an inexpensive Wifi Module for Arduino that supports 802.11 b/g/n protocols and it can also run Arduino code. There are multiple versions of this SOC. Some require serial to USB adapter for programming and some have micro USB port. They also vary by amount of GPIO ports and memory they have.

List of parts that I also used for this project:

WeMos D1 ESP8266
Relay module
MB102 Breadboard Power Supply Module
Old notebooks power adapter

For assembly I connected notebook’s PSU to MB102 PSU module, MB102 to ESP8266 with USB cable and GPIO ports 0, 2 and ground on ESP8266 to Relay module.

I modified ESP8266 library example code and uploaded it on the WeMos ESP8266:

#include <ESP8266WiFi.h>

const char* ssid = "SSID";
const char* password = "wifi password";

// Create an instance of the server
// specify the port to listen on as an argument
WiFiServer server(80);

void setup() {
  Serial.begin(115200);
  delay(10);

  // prepare GPIO2
  pinMode(2, OUTPUT);
  digitalWrite(2, 0);
  
  // Connect to WiFi network
  Serial.println();
  Serial.println();
  Serial.print("Connecting to ");
  Serial.println(ssid);
  
  WiFi.begin(ssid, password);
  
  while (WiFi.status() != WL_CONNECTED) {
    delay(500);
    Serial.print(".");
  }
  Serial.println("");
  Serial.println("WiFi connected");
  
  // Start the server
  server.begin();
  Serial.println("Server started");

  // Print the IP address
  Serial.println(WiFi.localIP());
}

void loop() {
  // Check if a client has connected
  WiFiClient client = server.available();
  if (!client) {
    return;
  }
  
  // Wait until the client sends some data
  Serial.println("new client");
  while(!client.available()){
    delay(1);
  }
  
  // Read the first line of the request
  String req = client.readStringUntil('\r');
  Serial.println(req);
  client.flush();
  
  // Match the request
  int stat;
  if (req.indexOf("/gpio/0") != -1){
    digitalWrite(2, 0);
  }
  else if (req.indexOf("/gpio/1") != -1){
    digitalWrite(2, 1);
  }
  else if (req.indexOf("/status") != -1){
  }
  else {
    Serial.println("invalid request");
    client.stop();
    return;
  }

  // Set GPIO2 according to the request
  stat = digitalRead(2);
  
  client.flush();

  // Prepare the response
  String s = "HTTP/1.1 200 OK\r\nContent-Type: text/html\r\n\r\n<!DOCTYPE HTML>\r\n<html>\r\n";
  s += (stat)?"high":"low";
  s += "</html>\n";

  // Send the response to the client
  client.print(s);
  delay(1);
  Serial.println("Client disonnected");

  // The client will actually be disconnected 
  // when the function returns and 'client' object is detroyed
}

#include <ESP8266WiFi.h>

const char* ssid = "SSID";

const char* password = "wifi password";

// Create an instance of the server

// specify the port to listen on as an argument

WiFiServer server(80);

void setup() {

Serial.begin(115200);

delay(10);

// prepare GPIO2

pinMode(2, OUTPUT);

digitalWrite(2, 0);

// Connect to WiFi network

Serial.println();

Serial.print("Connecting to ");

Serial.println(ssid);

WiFi.begin(ssid, password);

while (WiFi.status() != WL_CONNECTED) {

delay(500);

Serial.print(".");

}

Serial.println("");

Serial.println("WiFi connected");

// Start the server

server.begin();

Serial.println("Server started");

// Print the IP address

Serial.println(WiFi.localIP());

}

void loop() {

// Check if a client has connected

WiFiClient client = server.available();

if (!client) {

return;

}

// Wait until the client sends some data

Serial.println("new client");

while(!client.available()){

delay(1);

}

// Read the first line of the request

String req = client.readStringUntil('\r');

Serial.println(req);

client.flush();

// Match the request

int stat;

if (req.indexOf("/gpio/0") != -1){

digitalWrite(2, 0);

}

else if (req.indexOf("/gpio/1") != -1){

digitalWrite(2, 1);

}

else if (req.indexOf("/status") != -1){

}

else {

Serial.println("invalid request");

client.stop();

return;

}

// Set GPIO2 according to the request

stat = digitalRead(2);

client.flush();

// Prepare the response

String s = "HTTP/1.1 200 OK\r\nContent-Type: text/html\r\n\r\n<!DOCTYPE HTML>\r\n<html>\r\n";

s += (stat)?"high":"low";

s += "</html>\n";

// Send the response to the client

client.print(s);

delay(1);

Serial.println("Client disonnected");

// The client will actually be disconnected

// when the function returns and 'client' object is detroyed

}

Module automatically connects to wifi when powered and receives an IP address from router (192.168.1.45 for example). It’s IP may change every time module disconnects from wifi, so I assigned it static IP address on my router.

You can switch GPIO on by sending HTML request to “http://[ESP8266s ip address]/gpio/0” and to turn it off “~/gpio/1”. This is done simply by visiting url in a web browser.
Disadvantage of the code from libraries example is that you can’t tell whether GPIO is on or off. I modified it so that html response includes info about its status when you visit ~/status.

Turning the air conditioner on by typing http://192.168.1.45/gpio/0 into a browser and making sure that it’s on or off by visiting http://192.168.1.45/status it’s not very practical, so I made a simple web interface and added it to my homes dashboard webpage.

<?php
//get the GPIO status
$html = file_get_contents('http://192.168.1.45/status');
if (strpos($html, 'low') !== false) {
    $status = 0;
}
else {
  $status = 1;
}

  if ($_POST["15"] == "1") {
    if ($status == 1) {
      file_get_contents('http://192.168.1.45/gpio/0');
      $status = 0;
    }
    elseif ($status == 0) {
      file_get_contents('http://192.168.1.45/gpio/1');
      $status = 1;
    }
  }
?>

<!DOCTYPE html>
<html lang="en">
<head>
  <title>Switch</title>
  <meta charset="utf-8">
  <meta name="viewport" content="width=device-width, initial-scale=1">
  <link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.6/css/bootstrap.min.css">
</head>
<body>

<div class="container">
  <div class="col-sm-3">
       <h3>Air conditioner</h3>
        <form  id="form" name="test" action="index.php" method="post">
          <input type="hidden" name="15" value="1"></input>
          <input type="submit" class="<?php if($status == 1) {print("btn btn-primary btn-lg btn-block");} else {print("btn btn-secondary btn-lg btn-block button");} ?>" value="<?php if($status == 1) {print("Turn Off");} else {print("Turn On");} ?>"></input>
        </form>
    </div>
    </div>
</body>
</html>

<?php

//get the GPIO status

$html = file_get_contents('http://192.168.1.45/status');

if (strpos($html, 'low') !== false) {

$status = 0;

}

else {

$status = 1;

}

if ($_POST["15"] == "1") {

if ($status == 1) {

file_get_contents('http://192.168.1.45/gpio/0');

$status = 0;

}

elseif ($status == 0) {

file_get_contents('http://192.168.1.45/gpio/1');

$status = 1;

}

<!DOCTYPE html>

<head>

<title>Switch</title>

</head>

<body>

<h3>Air conditioner</h3>

<input type="submit" class="<?php if($status == 1) {print("btn btn-primary btn-lg btn-block");} else {print("btn btn-secondary btn-lg btn-block button");} ?>" value="<?php if($status == 1) {print("Turn Off");} else {print("Turn On");} ?>"></input>

</form>

</div>

</body>

</html>

It displays a button with text “Turn on” or “Turn off” depending on the GPIOs current status. When you click it, it sends a html request to the module to change its GPIO state.
You can use as many ESP8266 modules as you want and manage them from a centralized web application.

Edit: Someone on Reddit requested code for managing multiple ESP8266s. So here is the code. To add new module, just add its IP address and name in the array.

<?php
$devices = array(
    '192.168.1.66' => 'Light1',
    '192.168.1.45' => 'Light2',
    '192.168.1.47' => 'AirConditioner');

$i = 0;
foreach ($devices as $ip => $name) {
    $html = file_get_contents('http://' . $ip .'/status');
    if (strpos($html, 'low') !== false) {
        $status[$i] = 0;
    }
    else {
      $status[$i] = 1;
    }
    if ($_POST[$name] == "1") {
      if ($status[$i] == 1) {
        file_get_contents('http://'. $ip . '/gpio/0');
        $status[$i] = 0;
      }
      elseif ($status[$i] == 0) {
        file_get_contents('http://'. $ip . '/gpio/1');
        $status[$i] = 1;
      }
    }
  $i++;
}
?>
 
<!DOCTYPE html>
<html lang="en">
<head>
  <title>Switch Control Interface</title>
  <meta charset="utf-8">
  <meta name="viewport" content="width=device-width, initial-scale=1">
  <link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.6/css/bootstrap.min.css">
</head>
<body>
 
  <div class="container">
    <div class="col-sm-4">
    <h2>Switch Control Interface</h2>
    <? $i=0; foreach ($devices as $ip => $name) { ?>
       <h3><?echo $name;?></h3>
          <form  id="form" name="test" action="index.php" method="post">
            <input type="hidden" name="<? echo $name; ?>" value="1"></input>
          <input type="submit" class="<? print ($status == 1 ? 'btn btn-primary btn-lg btn-block' : 'btn btn-secondary btn-lg btn-block button');?>" value="<?php print ($status == 1 ? 'Turn Off' : 'Turn On');?>"></input>
          </form>
    <?php $i++; } ?>
    </div>
  </div>
</body>
</html>

<?php

$devices = array(

'192.168.1.66' => 'Light1',

'192.168.1.45' => 'Light2',

'192.168.1.47' => 'AirConditioner');

$i = 0;

foreach ($devices as $ip => $name) {

$html = file_get_contents('http://' . $ip .'/status');

if (strpos($html, 'low') !== false) {

$status[$i] = 0;

}

else {

$status[$i] = 1;

}

if ($_POST[$name] == "1") {

if ($status[$i] == 1) {

file_get_contents('http://'. $ip . '/gpio/0');

$status[$i] = 0;

}

elseif ($status[$i] == 0) {

file_get_contents('http://'. $ip . '/gpio/1');

$status[$i] = 1;

}

$i++;

}

<!DOCTYPE html>

<head>

<title>Switch Control Interface</title>

</head>

<body>

<h2>Switch Control Interface</h2>

<? $i=0; foreach ($devices as $ip => $name) { ?>

<input type="hidden" name="<? echo $name; ?>" value="1"></input>

<input type="submit" class="<? print ($status == 1 ? 'btn btn-primary btn-lg btn-block' : 'btn btn-secondary btn-lg btn-block button');?>" value="<?php print ($status == 1 ? 'Turn Off' : 'Turn On');?>"></input>

</form>

<?php $i++; } ?>

</div>

</body>

</html>

Here is a video demonstration of last years system. Front-end webapp is the same and it functions the same.