Ultrasonic Sensor - Monitoring Distance via WebSocket

Tutorial Video

Hardware

• PHPoC Blue (+ USB WLAN) or PHPoC Black (+ Ethernet cable)
• Micro USB to USB Cable (to upload source code to PHPoC Device)
• Ultrasonic Sensor
• Jumper wires

About Ultrasonic Sensor

Ultrasonic sensor HC-SR04 is used to measure distance to an object by using ultrasonic waves. The ultrasonic sensor HC-SR04 includes four pins:

• VCC pin.
• GND pin.
• TRIG pin: this pin receives a 10-microsecond pulse from controller to emit ultrasonic wave.
• ECHO pin: this pin outputs a pulse when receiving echo ultrasonic wave. The duration of pulse is used to calculate the distance.

How the ultrasonic sensor works:

• If receiving 10-microsecond pulse on TRIG pin , ultrasonic sensor automatically emits 40KHz ultrasonic wave.
• If there is an obstacle, ultrasonic wave is reflected back.
• Ultrasonic sensor measures duration of time from emiting ultrasonic wave to receiving the echo ultrasonic wave. And then ultrasonic sensor generate a pulse with the measured duration on ECHO pin.

How to use ultrasonic sensor:

• Connect TRIG pin of ultrasonic sensor to HT0 pin of PHPoC device. Set HT0 timer to "ouput pulse" mode.
• Connect ECHO pin of ultrasonic sensor to HT1 pin of PHPoC device. Set HT1 timer to "capture" mode.
• Use HT0 timer to generate 10-microsecond pulse.
• Use HT2 timer to capture the pulse from ECHO pin.
• Calculate distance based on the duration of captured pulse. The duration of pulse is the travel time of ultrasonic wave. Travel speed of ultrasonic wave is about 340 m/s. Travel distance is calculated according to the formula: distance = speed * time
• Distance to obstacle is half of the travel distance of ultrasonic wave.

Wiring Diagram



Quick Steps

Source code of this example is a part of PHPoC Support Packet (PSP). You need to:

• Download PHPoC Support Package.
• Upload example\p4s\04.html5_text\03.ht_ultrasonic to PHPoC Blue/Black.
• Configure network parameters (e.g. WiFi SSID, password, IP address ...).
• Click "Run" button on PHPoC Debugger.
• Access webpage on PHPoC using Web Browser on your PC or smart phone (See How To).

If you use PHPoC for the first time, see How To Use PSP.


Source Code

Source files includes:

• init.php: this file is run when PHPoC system is powered or reset. It is used to specify which file is run is system loop.
• task0.php: this file is run in system loop of PHPoC devices. It acts as WebSocket server and also interacts with ultrasonic sensor.
• index.php: this file contains source code of web page.It is only run in response to request from Web Browser. It contains webpage (user interface) and acts WebSocket client.

init.php

This file is run when PHPoC system is powered or reset. It is used to specify that task0.php is run is system loop.

<?php

system("php task0.php");

?>

task0.php

[Full Code]

<?php

if(_SERVER("REQUEST_METHOD"))
 exit; // avoid php execution via http request

include "/lib/sd_340.php";
include "/lib/sn_tcp_ws.php";

// setup trigger pulse timer
ht_ioctl(0, "set mode output pulse");
ht_ioctl(0, "set div us");
ht_ioctl(0, "set repc 1");
ht_ioctl(0, "set count 5 10"); // 10us pulse width

// setup echo capture timer
ht_ioctl(1, "reset");
ht_ioctl(1, "set div us");
ht_ioctl(1, "set mode capture toggle");
ht_ioctl(1, "set trigger from pin rise");
ht_ioctl(1, "set repc 4");

ws_setup(0, "WebConsole", "text.phpoc");

while(1)
{
 if(ws_state(0) == TCP_CONNECTED)
 {
  ht_ioctl(1, "start"); // we should start capture timer first
  ht_ioctl(0, "start"); // start trigger pulse

  usleep(100000); // sleep 100ms
  ht_ioctl(1, "stop");

  // 1st capture value ("get count 0") is always zero.
  // we should get 2nd capture value;
  $us = ht_ioctl(1, "get count 1");

  $dist = $us * 340.0 / 2; // us to meter conversion
  $dist = $dist / 10000; // meter to centimeter conversion

  ws_write(0, sprintf("%d us, %.1f Cm\r\n", $us, $dist));

  sleep(1);
 }
}

?>

[Explanation]

Source code of this file does:

• Setup HT0 timer to generate pulse and HT1 timer to capture signal.
• Setup and initialize WebSocket.

In infinite loop:

• Start capture timer to generate a pulse
• Start the trigger pulse timer to capture echo signal
• Get duration of captured pulse
• Calculate distance according to the duration of captured pulse
• Send distance from sensor to obstacle to Web Browser via WebSocket.

index.php

[Full Code]

<html>
<head>
<title>PHPoC / <?echo system("uname -i")?></title>
<meta name="viewport" content="width=device-width, initial-scale=0.7">
<style>
body { text-align:center; }
textarea { width:400px; height:400px; padding:10px; font-family:courier; font-size:14px; }
 </style>
<script>
var ws;
var wc_max_len = 32768;
function ws_onopen()
{
 document.getElementById("ws_state").innerHTML = "OPEN";
 document.getElementById("wc_conn").innerHTML = "Disconnect";
}
function ws_onclose()
{
 document.getElementById("ws_state").innerHTML = "CLOSED";
 document.getElementById("wc_conn").innerHTML = "Connect";

 ws.onopen = null;
 ws.onclose = null;
 ws.onmessage = null;
 ws = null;
}
function wc_onclick()
{
 if(ws == null)
 {
  ws = new WebSocket("ws://<?echo _SERVER("HTTP_HOST")?>/WebConsole", "text.phpoc");
  document.getElementById("ws_state").innerHTML = "CONNECTING";

  ws.onopen = ws_onopen;
  ws.onclose = ws_onclose;
  ws.onmessage = ws_onmessage;
 }
 else
  ws.close();
}
function ws_onmessage(e_msg)
{
 e_msg = e_msg || window.event; // MessageEvent

 var wc_text = document.getElementById("wc_text");
 var len = wc_text.value.length;

 if(len > (wc_max_len + wc_max_len / 10))
  wc_text.innerHTML = wc_text.value.substring(wc_max_len / 10);

 wc_text.scrollTop = wc_text.scrollHeight;
 wc_text.innerHTML += e_msg.data;
}
function wc_clear()
{
 document.getElementById("wc_text").innerHTML = "";
}
</script>
</head>
<body>

<h2>
<p>
Web Console : <span id="ws_state">CLOSED</span><br>
</p>
<textarea id="wc_text" readonly="readonly"></textarea><br>
<button id="wc_conn" type="button" onclick="wc_onclick();">Connect</button>
<button id="wc_clear" type="button" onclick="wc_clear();">Clear</button>
</h2>

</body>
</html>

[Explanation]

Source code of index.php file is composed of HTML, CSS, JavaScript and PHPoC code.

PHPoC code is interpreted on on PHPoC device.

PHPoC code may add/update the content of HTML, CSS or JavaScript code. Once PHPoC code is interpreted in PHPoC, the remaining code is client-side code and it is returned to Web Browser. Web Browser receives this code and interpret it to display the webpage.

• HTML: describes the structure of Web pages
• CSS: describes how HTML elements are to be displayed
• JavaScript: This code:
  - Receive data (distance from sensor to obstacle of ultrasonic sensor) from PHPoC devices via WebSocket,
  - Display distance from sensor to obstacle on webpage
  

For detail explanation, see How to Monitor Sensors/Devices via WebSocket




See Also

• Ultrasonic Sensor - How to Use Ultrasonic Sensor Sensor.
• Ultrasonic Sensor - Monitoring Distance from Webpage using Hypertext.
• Ultrasonic Sensor - Monitoring Distance from Webpage with Image.

Other Resources

• PHPoC System Files
• How PHPoC System Works
• How To Use PHPoC Support Package
• WebSocket
• How to Create Embedded Web Apps with WebSocket on PHPoC
• How to Control Devices via Web Browser
• How to Control Devices via HTTP Request
• How to Control Devices via WebSocket
• How to Monitor Sensors/Devices via Web Browser
• How to Monitor Sensors/Devices via HTTP Request
• How to Monitor Sensors/Devices via WebSocket
• How to Access Web Apps on PHPoC