Using Multiple Phidgets

Before opening a channel, it is important to set enough of the matching properties to ensure the desired device channel is matched. By default, the matching code in the Phidget library will match the first available device channel that is of the correct class. For example, if two temperature sensor devices are connected to a computer, it is undefined which will attach when the device serial number is not specified before the channel is opened.

Using the Channel ID

Each channel exported by a Phidget device has an id, normally starting at 0. The channel property must be set to ensure the device channel the Phidget software library matches is right one. If a 4-channel temperature sensor is connected, and the channel property is not specified, the matching code will attach to channel 0 if available, and the next available channel if not.

Set the channel id with the Channel property.

Using the Hub Port

VINT hubs have a number of ports that VINT devices can be connected to. To ensure the correct VINT device is attached, the hub port must be specified. If two temperature sensors are attached to the same hub, and the hub port is not specified prior to opening a channel, it is undefined which temperature sensor will be attached.

Set the hub port with the HubPort property.

Using the Serial Number

Each Phidget has a unique serial number (VINT devices inherit the serial number of the hub). When there is more than one device that exports the same channel class, the device serial number must be specified to ensure the channel on the desired device is matched. The device serial number can be found on a label on the bottom of the Phidget, or determined by reading the DeviceSerialNumber property.

Set the device serial number with the DeviceSerialNumber property.

Using the Label

Most Phidgets can be assigned a label that may be used as a human-readable way to reference them (VINT devices inherit the serial number of the hub). In software that will be distributed, or cannot easily be modified it is useful to attach to channels based on the label of the device. This way, the device can be labelled prior to running the software, and the new device will be matched

Set the device label with the DeviceLabel property.

Some limitations are:

In Windows, label can be read on any Phidget that has a serial number, but label can only be written for Phidgets that support firmware upgrading.
Some programming languages do not support writing to labels. See the Phidget22 API.

Code Examples

For example, in Java, this would be:

 ch.setDeviceSerialNumber(12345);  // match device 12345
 ch.setHubPort(4);                 // match hub port 4
 ch.setChannel(1);                 // match channel 1 port 4 dev 12345
 ch.open();                        // start matching

Or in C:

 Phidget_setDeviceSerialNumber((PhidgetHandle)ch, 12345);  // match device 12345
 Phidget_setHubPort((PhidgetHandle)ch, 4);                 // match hub port 4
 Phidget_setChannel((PhidgetHandle)ch, 1);                 // match channel 1 port 4 dev 12345
 Phidget_open((CPhidgetHandle)ch);                         // start matching

Distinguishing Events

If you are using event-driven code, once you have correctly opened multiple Phidgets of different types, they will have different event handlers and hence you will know what Phidget triggered which event. If you are using multiple Phidgets of the same type, or you are trying to determine within general events (such as Attach Events) which Phidget triggered the event, you can then check the serial number (or device type) of the triggering device and act accordingly.

For example, in Java, your attach event handler might look like this:

    detachHandler = new DetachListener() { 
        public void detached(DetachEvent event) {
            int serialNumber = ((Phidget)event.getSource()).getSerialNumber();
            // Do something according to serialNumber
    }    }

Or in C:

    int AttachHandler(CPhidgetHandle device, void *userptr) {
	int serialNo;
	CPhidget_getSerialNumber(device, &serialNo);
         // Do something according to serialNumber
    }

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