Use Phidgets Wirelessly with the SBC

The project described here is a basic network control program for an LED plugged in to an SBC.

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 with C/C++

As with any of our described projects, Phidgets takes care of the electrical component design. This project demonstrates what the SBC already does naturally from the time it ships. If you want something more powerful and flexible to control Phidgets over a network, you may be interested in these other Application Guides:

• Web Page on the SBC - Controlling Phidgets over the web using CGI
• Web Server on the SBC - Controlling Phidgets over the web using a full self-contained webserver embedded in C code

Time: About an hour

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 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.

Phidgets

For this, you will need:

• A 1072 0 - PhidgetSBC2, set up as per the 1072 - Getting Started guide
  • This is the SBC that this guide used; others will probably work fine as well
• An LED, such as one of the ones from Phidgets (many part numbers starting at 3600), attached to digital output port 0 (long wire) and ground (short wire)

Code

On your external computer, you can use this code to control the Interface Kit (which is attached to the SBC) over the network:

#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;
}

Some highlights:

• Line 14 is the line that actually opens the Interface Kit over the network.
  • Notice that there is no mention of the SBC, or any SBC object.
  • The SBC will simply act as a transparent pipe between the Phidget and your computer.
• Lines 25-31 blink the LED quickly; however, the flashing will barely be visible and the LED will simply appear to be on