Using Multiple Phidgets

Chances are your project with Phidgets it going to involve more than one Phidget channel. Luckily, making a program that deals with multiple Phidgets is done in much the same way as making a program that only deals with one. If you haven't read them yet, we recommend first reading the pages on What is a Phidget? and Phidget Programming Basics to better understand the contents of this page.

This video explains the process of using multiple Phidgets in your program:

The Basics

To use more than one Phidget channel in you program, simply repeat the Create, Address, and, Open process for each channel, and remember to Close them all when done.

Addressing Channels

When you are using more than one Phidget channel in your program, you are going to have to specify some addressing parameters to ensure each software channel connects to the right Phidget.

Full descriptions of all the addressing parameters can be found on the Addressing Phidgets page.

Example

For example, to open two Phidgets, the code might be:

//Set up the first channel as normal
TemperatureSensor ch = new TemperatureSensor();
ch.setDeviceSerialNumber(12345);
ch.setHubPort(4);
ch.setChannel(0);
ch.open(5000);

//For a second channel, simply repeat the process with different addressing information
TemperatureSensor ch1 = new TemperatureSensor();
ch1.setDeviceSerialNumber(12345); 
ch1.setHubPort(3);
ch1.setChannel(0);
ch1.open(5000);
 
//Do stuff with your Phidgets here...

//Remember to close the channels when done
ch.close();
ch1.close();

//Set up the first channel as normal
ch = TemperatureSensor()
ch.setDeviceSerialNumber(12345)
ch.setHubPort(4)
ch.setChannel(0)
ch.openWaitForAttachment(5000)

//For a second channel, simply repeat the process with different addressing information
ch1 = TemperatureSensor()
ch1.setDeviceSerialNumber(12345)
ch1.setHubPort(3)
ch1.setChannel(0)
ch1.openWaitForAttachment(5000)
 
//Do stuff with your Phidgets here...

//Remember to close the channels when done
ch.close()
ch1.close()

//Set up the first channel as normal
TemperatureSensor ch = new TemperatureSensor();
ch.DeviceSerialNumber = 12345;
ch.HubPort = 4;
ch.Channel = 0;
ch.Open(5000);

//For a second channel, simply repeat the process with different addressing information
TemperatureSensor ch1 = new TemperatureSensor();
ch1.DeviceSerialNumber = 12345; 
ch1.HubPort = 3;
ch1.Channel = 0;
ch1.Open(5000);
 
//Do stuff with your Phidgets here...

//Remember to close the channels when done
ch.Close();
ch1.Close();

//Set up the first channel as normal
PhidgetTemperatureSensorHandle ch;
PhidgetTemperatureSensor_create(&ch);

Phidget_setDeviceSerialNumber((PhidgetHandle)ch, 12345);
Phidget_setHubPort((PhidgetHandle)ch, 4);
Phidget_setChannel((PhidgetHandle)ch, 0);
Phidget_openWaitForAttachment((PhidgetHandle)ch, 5000);

//For a second channel, simply repeat the process with different addressing information
PhidgetTemperatureSensorHandle ch1;
PhidgetTemperatureSensor_create(&ch1);

Phidget_setDeviceSerialNumber((PhidgetHandle)ch1, 12345);
Phidget_setHubPort((PhidgetHandle)ch1, 4);
Phidget_setChannel((PhidgetHandle)ch1, 0);
Phidget_openWaitForAttachment((PhidgetHandle)ch1, 5000);
 
//Do stuff with your Phidgets here...

//Remember to close the channels when done
Phidget_close((PhidgetHandle)ch);
Phidget_close((PhidgetHandle)ch1);
PhidgetTemperatureSensor_delete(&ch);
PhidgetTemperatureSensor_delete(&ch1);

Distinguishing Events

When using events, you can either create separate events for each device, or handle multiple devices with the same event (or some combination of both). In the case where multiple devices are handled by the same event handler, the addressing properties of the channel can be read to determine what device channel the event is from.

The channel that fired the event will always be available in the event handler, regardless of language, though its exact form changes from language to language. In most languages, it is the first parameter in the parameter list, whether it's called source or sender or ch. In Java, you will need to call getSource() on the event parameter to get the Phidget that caused the event. In JavaScript, you will use the this keyword in your event handler.

Referencing Other Phidgets from Events

When using multiple Phidgets in the same program, you may want to access one Phidget from the within an event caused by another. To do so, there are three basic methods of making the Phidget available, depending of the programming language you are using:

C# and Java

In C# and Java, chances are your event handlers are defined in the same namespace (or class) as the Phidget handles. In this case, you can simply reference Phidgets in the event handlers the same way as you would in the rest of your code.

Python and JavaScript

Python and JavaScript are both dynamically interpreted, and objects follow a less rigid structure than in other languages. In these languages, to access another Phidget from an event handler, you can add the second Phidget's handle to the Phidget triggering the event. Then, you may access the second Phidget using the self parameter of the event.

For example:

def onStateChangeHandler(self, state):
    #Be sure the other Phidget you are trying to access is attached before using it
    if(self.output.getAttached()):
        self.output.setState(state)
    print("State %f" % state)
    return 0

button = DigitalInput()
output = DigitalOutput()

#Addressing info here

#Here we create an attribute of input called "output", and assign it the handle for output
#You can use this exact line in JavaScript
button.output = output
button.setOnStateChangeHandler(onStateChangeHandler)

output.openWaitForAttachment(5000)
button.openWaitForAttachment(5000)

function stateChange(state) {
    //Be sure the other Phidget you are trying to access is attached before using it
    if(this.output.getAttached())
        this.output.setState(state);
    console.log("State " + state)
}
...
    var input = new phidget22.DigitalInput();
    var output = new phidget22.DigitalOutput();
...
    //Here we create an attribute of input called "output", and assign it the handle for output
    input.output = output;
    input.onStateChange = stateChange;

    output.open();
    input.open();

C

In C, all event handler declarations have a context pointer that can be pointed at any object you choose. This can be a set of relevant data, or even a Phidget handle. If you pass a Phidget handle as the context pointer as a event, you can access the passed Phidget from the event as follows:

static void CCONV onStateChangeHandler(PhidgetDigitalInputHandle pdih, void *ctx, int state) {
    int attached;
    //Extract our output handle from the context pointer
    PhidgetDigitalOutputHandle out = (PhidgetDigitalOutputHandle)ctx;

    //Be sure the other Phidget you are trying to access is attached before using it
    Phidget_getAttached((PhidgetHandle)out, &attached);

    if(attached)
        PhidgetDigitalOutput_setState(out, state);

    printf("[State Event] -> State: %d\n", state);
}

int main() {
    PhidgetDigitalInputHandle ch = NULL;
    PhidgetDigitalOutputHandle out = NULL;

    PhidgetDigitalInput_create(&ch);
    PhidgetDigitalOutput_create(&out);
    
    //Addressing info here

    //Here we pass the handle for "out" as the context pointer so we can access it from the event
    PhidgetDigitalInput_setOnStateChangeHandler(ch, onStateChangeHandler, out);


    if (SetAttachDetachError_Handlers((PhidgetHandle)ch))
        goto error;
    
    Phidget_openWaitForAttachment((PhidgetHandle)out, 5000);
    Phidget_openWaitForAttachment((PhidgetHandle)ch, 5000);

    //The rest of your code here

}

Further Reading

Phidget Programming Basics - Here you can find the basic concepts to help you get started with making your own programs that use Phidgets.

Data Interval/Change Trigger - Learn about these two properties that control how much data comes in from your sensors.

Polling vs. Events - Your program can gather data in either a polling-driven or event-driven manner. Learn the difference to determine which is best for your application.

Logging, Exceptions, and Errors - Learn about all the tools you can use to debug your program.

Phidget Network Server - Phidgets can be controlled and communicated with over your network- either wirelessly or over ethernet.

Best Phidgets Practices - Good programming habits that will save you from common problems when writing code for your Phidgets.