Use Phidgets Wirelessly with the SBC

The project described here is a self-contained web server on the Phidget Single Board Computer (SBC). We compose and serve a complete HTTP page within C, and include Phidget data on it. We also accept data to control attached Phidgets in our request.

Practical concepts covered are (click on links to see other projects on that topic): Using the Phidget SBC Using Phidgets over the Webservice Using Phidgets Wirelessly Using Phidgets with C/C++

File:TBD

As with any of our described projects, Phidgets takes care of the electrical component design. Here, we also provide in-depth instructions on installing external libraries on the SBC from source, and from an SVN trunk. We then show how to use the microhttpd.h library within C code to communicate with and control attached Phidgets.

Note: This is a complex way of doing something that the SBC can do much more simply. This page uses the simple example of using an Interface Kit over the network to demonstrate the much more complex concept of using embedded C HTTP servers. An embedded server is a powerful beast, and wanting to create one probably means you've grown needs above and beyond our simple Application Guides. The simpler guides are:

• If you just want to get Phidget data over the network, the SBC already does this naturally from the time it ships. We show an application in the Use Phidgets Wirelessly with the SBC guide.

Time: About a day

Special Needed Tools: A Phidget SBC, Ethernet and power cords (or Wireless), an LED, and your computer.

You should have already worked through the 1072 - Getting Started page before this one to have set up the network on your SBC and obtained its IP or local link address.

Introduction

When the SBC is powered on and connected to a network, it automatically handles any network requests for the Phidgets attached to it. All sensor and other Phidget data is broadcast over the local network as it changes, and all incoming Phidget control requests to the SBC over the local network are directed to the appropriate Phidgets.

This Webservice system looks something like this:

To create these requests to control the attached Phidgets, or to receive incoming sensor data, we write code on the controlling and receiving computer. This application guide simply blinks an LED plugged in to the SBC, and does so over the network.

Code

#include <stdio.h>
#include <stdlib.h>
#include "phidget21.h"

int main(int argc, char* argv[]) {
 
    int result;
    int outputState;
    int i; 

	CPhidgetInterfaceKitHandle interfaceKit = 0;
    CPhidgetInterfaceKit_create(&interfaceKit);
 
    CPhidget_openRemoteIP((CPhidgetHandle)interfaceKit, -1, "phidgetsbc.local", 5001, NULL);
 
    result = CPhidget_waitForAttachment((CPhidgetHandle)interfaceKit, 10000);
    if (result) {
        printf("No Device!\n");
        return 0;
    }

    outputState = 1;
    CPhidgetInterfaceKit_setOutputState(interfaceKit, 0, outputState);

    for (i = 0; i < 1000; i++) {
    
        if (outputState) { outputState = 0; }
        else { outputState = 1; }

        CPhidgetInterfaceKit_setOutputState(interfaceKit, 0, outputState);
    }

    CPhidgetInterfaceKit_setOutputState(interfaceKit, 0, 0);

    CPhidget_close((CPhidgetHandle)interfaceKit);
    CPhidget_delete((CPhidgetHandle)interfaceKit);

    return 0;
}