Pi PHP Controls

I’ve been trying to teach my kids PHP,  below are some notes on how to get a PHP page to control Pi GPIO outputs. For motor controls we use the Pimoroni ExplorerHat Pro and it is possible to address the ExplorerHat pins directly with gpio calls. However other shields or tops like PiFace Digital could also be used.

Loading PHP

On the Raspberry Pi you will need to load both a web server and PHP. There are a number of good web servers to load. We picked Apache because it is well documented and more mainstream.

There are some good installation procedure for installing Apache and PHP on the Raspberry Pi. A minimalist installation would be:

sudo apt-get install apache2 -y
sudo apt-get install php5 libapache2-mod-php5 -y

If everything is installed correctly the Apache home directory should be: /var/www/html.

To test that your installation is working open a browser on the Pi and go to: http://localhost. If the default (index.html) page comes up then you’ve install Apache correctly.

ExplorerHat Pro GPIO Pinouts

Typically we use the Python interface to talk to the ExplorerHat Pro. If you use PHP you will need to address the ExplorerHat Pro GPIO pins directly.

ExplorerHat  BCM wPi
Motor 1 Forward 19 24
Motor 1 Backward 20 28
Motor 2 Forward 21 29
Motor 2 Backward 26 25
LED 1 4 7
LED 2 17 0
LED 3 27 2
LED 4 5 21
Output 1 22 31
Output 2 26 32
Output 3 23 33
Output 4 27 36

PHP Interfacing to Pi GPIO

There are a few ways to access the GPIO pins in PHP:
1. use a PHP library
2. shell to the gpio command

Using a PHP library allows for a standard PHP interface, with an object model.

From testing I found that the PHP libraries were not as flexible as the standard gpio command. For example you could not access extended GPIO pin numbers (i.e. 200).

GPIO Command Line Utility

PHP can shell out to the gpio command line utility. I liked this approach because I could test the actions manually before putting them into a PHP web page.

A simple gpio read example would be:

<html lang="en">
<head>
</head>
<body>
<?php
$ret = shell_exec('gpio read 7');
echo "Pin 7 status = " . $ret;
?>
</body>
</html>

And a gpio write example (with reading back the result) would be:

<html>
<head>
</head>
<body>
<?php
exec("gpio write 7 1");
$ret = shell_exec('gpio read 7');
echo "Pin 7 status = " . $ret;
?>
</body>
</html>

 

PHP Forms

For many Pi projects button interfaces are all that is required. In the Web design this is not typical so it is important to determine which button is pushed. One approach to this problem is to give all the buttons the same name:


  
  
  
  


Then in the PHP code look for a value for this form variable:

<?php
// define the GPIO pins for the motor ouptput (Note: PiFace pins start at 200)
$leftpin = 24;
$rightpin = 29;

if (isset($_POST['submit'])) {
	switch ($_POST['submit']) {
		case "go":
			exec("gpio write " . $leftpin . " 1");
			exec("gpio write " . $rightpin . " 1");
			break;
		case "stop":
			exec("gpio write " . $leftpin . " 0");
			exec("gpio write " . $rightpin . " 0");
			break;
		case "left":
			exec("gpio write " . $leftpin . " 1");
			exec("gpio write " . $rightpin . " 0");
			break;
		case "right":
			exec("gpio write " . $leftpin . " 0");
			exec("gpio write " . $rightpin . " 1");
			break;
	}
}
?>

Mobile CCS Templates

There are quite a few good mobile templates to choose from. [Bootstrap](http://getbootstrap.com/) is one of the most popular frameworks, and for Pi applications it seems to be a good fit. A simple four button example would be:

<!DOCTYPE html>
<html lang="en">
<head>
  <title>PHP/Pi Rover Controls</title>
  <meta charset="utf-8">
  <meta name="viewport" content="width=device-width, initial-scale=1">
  <link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.7/css/bootstrap.min.css">
  <script src="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.7/js/bootstrap.min.js"></script>
</head>
<body>
<div class="container">

  <h2>PI Four Button Example</h2>
  <form action="" method="post">
    <div class="form-group">

    <button type="submit" name="submit" class="btn-success btn-lg" style="width:100%" value="go">Forward</button>
    <button type="submit" name="submit" class="btn-info btn-lg" style="width:49%" value="left">Left</button>
    <button type="submit" name="submit" class="btn-info btn-lg" style="width:49%" value="right">Right</button>
    <button type="submit" name="submit" class="btn-danger btn-lg" style="width:100%" value="stop">Stop</button>
  </form>
</div>

</body>
</html>

Some of the key items are:

  • Add references in to the bootstrap ccs and js files
  • Add tags with the required class definitions:
    • the btn-lg class will make a large button, instead of standard sized btn 
    • different button colours are possible using btn-info, btn-success. btn-danger
    • Button width is defined with style=”width: xx%” . For multiple buttons the sum of the width needs to <100%

 

bootstrap4btns

Further Examples

Below are some pictures of a mobile rocket launcher project.  The Web page had two sections. The top section controlled bi-directional motors that were connected to a Explorer HAT Pro shield. The bottom section controlled the rocket launcher turret. The missile launcher was connected via a USB cable to the Pi. For the missile launcher program we created a Python app with command line options to set the action.

Screenshot

OLYMPUS DIGITAL CAMERA

Le gocart (Python Tkinter GUI)

For this project we wanted to control a Lego vehicle with a Python Tkinter app. Next we added a short cut to the Pi desktop and then we used VNC to see the Pi desktop and our app on a tablet.

Hardware Setup

Our hardware components were:

  • Raspberry Pi 3
  • Pimoroni ExplorerHat Pro – supports bi-directional DC motors
  • Dexter Connectors – allow 2 wire connections to Lego Mindstorms parts
  • 2 Lego Mindstorms motors
  • Portable USB charger
  • lots of Lego parts
  • 4 jumpers

le_gocart_parts

The Lego Mindstorms parts are little pricey but they allow you to make some pretty funky contraptions. The other thing that we like about the Mindstorms motors is that they have a lot of torque for a 5V DC motor.

There are a few options for the cabling (like cutting the cable and exposing the individual wires) we used the Dexter connectors that are breadboard friendly. ANA and GND connections on the Dexter side go to Motor + and Motor – on the ExplorerHat Pro board.

le_gocart_wiring

 

Python Tkinter

The Tkinter library allows you to create a simple graphic user interface (GUI) with components like: buttons, sliders, lists, text, labels etc.

For our interface we created a grid of 3 rows and 2 columns with 5 buttons. We made a simple motor function where we passed the speed and direction of the wheels. A negative speed is backwards, zero is stop, and a positive speed is forward.

import Tkinter
import explorerhat 

top = Tkinter.Tk()
top.title("Car Control")

explorerhat.motor.one.speed(0)
explorerhat.motor.one.speed(0)

#Define the buttons

def motor(Left,Right):
 explorerhat.motor.one.speed(Right)
 explorerhat.motor.two.speed(Left)

B_Left = Tkinter.Button(top, text ="Left", bg = "green", fg = "white", width= 15, height= 5, command = lambda: motor (50,0)).grid(row=1,column=1)
B_Right = Tkinter.Button(top, text ="Right", bg = "green", fg = "white", width= 15, height= 5, command = lambda: motor (0,50)).grid(row=1,column=2)
B_Forward= Tkinter.Button(top, text ="Forward", bg = "green", fg = "white", width= 15, height= 5, command = lambda: motor (50,50)).grid(row=2,column=1)
B_Backward = Tkinter.Button(top, text ="Backward", bg = "green", fg = "white", width= 15, height= 5, command = lambda: motor (-50,-50)).grid(row=2,column=2)
B_Stop = Tkinter.Button(top, text ="Stop", bg = "red", fg = "white", width= 33, height= 3, command = lambda: motor (0,0)).grid(row=3,column=1,columnspan=2)

top.mainloop()

VNC1

Pi Shortcut

To create a Pi shortcut, create a file:

nano $HOME/desktop/pi.desktop

Inside this file define the name, path, and icon info for your new application:

[Desktop Entry]
Name=Car Controls
Comment=Python Tkinter Car Control Panel
Icon=/home/pi/car1.png
Exec=python /home/pi/mycarapp.py
Type=Application
Terminal=false
Categories=None;

VNC (Virtual Network Computing)

VNC is install on the Raspbian image. To enable VNC run:

sudo raspi-config

Then select the interfacing option, and then select VNC and enable.

raspi-config-vnc

Finally you will need to define a VNC password and load some VNC software on your Tablet. There are a lot of packages to choose from. We have an Android table and we used RemoteToGo without any problems.

Note, when your Pi boots without a HDMI monitor connected the desktop resolution will be at a low setting (probably 800×600) this can be adjusted. For us we simply resized the desktop to fit our tablet screen.

Pi/Node-Red Car

The goal of the Pi/Node-Red car project was to create a small vehicle that can be controlled from a smart phone . For the project we used:

  • 1 Car chassis for Arduino ($15)
  • 1 Pimoroni Explorer HAT Pro  ($23)
  • 1 Portable microUSB charger
  • 1 USB WiFi Adapter
  • 4 short alligator clips and 4 connectors
  • Duct tape

The Arduino car chassis may require a small amount of assembly. Rather than soldering connections we like to use short alligator clips. It is not recommended to wire DC motors directly to a Raspberry Pi so the Pimoroni Explorer HAT Pro is used to connect the 2 DC motors.

The Raspberry Pi and the portable microUSB charger are secured to the top of the car chassis with duct tape. The left motor is wired to the motor 1 connectors on the Explorer Hat, and the right motor is wired to motor 2 connectors. Note you may have to do a little trial and error on the Explorer HAT “+” and “-” motor connections to get both wheels spinning in a forward direction.

The Explorer HAT Node-Red library is installed by:

 cd $HOME/.node-red
npm install node-red-dashboard 

The Web dashboard presentation is configured in the “dashboard” tab. For this example we create 2 groups: a control group to drive the vehicle, and a light group to turn on the Explorer Pro lights. Use the “+group” button to add a group, and the “edit” to change an existing group.
dash_conf

To control a motor, an “Explorer HAT” node and a dashboard button node are dropped and connected together. All the configuration is done in the button node . The button configure options are:

  • the group the button will appear in (Controls)
  • the size of the button (3×1 = 50% of width and narrow)
  • Topic, motor.one or motor.twois used for motor control
  • Payload, -100 = reverse, 0=stop, 100 = forward

Control_conf

The Explorer HAT has 4 colored LEDs. To toggle the LEDS, the topic is light.color with 1=ON, and 0=OFF . We thought that it would be fun to also add some Web dashboard button to control the colored lights.

light_conf

The Node-Red dashboard user interface is accessed by: ipaddress:1880/UI, so for example 192.168.1.102:1880/ui. Below is a picture that shows the final vehicle logic and the Web dashboard.

 

final_logic2