A simple touch based gui for small instruments. Developed using Python and PyQt. The aim was to have a simple lightweight library for integration with single board computer systems. This code has been tested on Raspberry Pi with a 7 in touchscreen. This has also been tested on desktop computer running Linux or Windows.

The package consists of a group of Python classes for

1. Displaying realtime data and measured quantities
2. Capturing user inputs through a touchscreen
3. Displaying and managing alarms

The screenshot below shows basic buttons and labels. The components and their functionality is described below.

Unlike conventional text labels, the puropose of the text label is to display process parameters. Hence they are designed for display name and value pair. In the image above the name (Message) is shown in the top left. The value (Hello World) is shown right. The text label is defined in ICTextLabel class. A text label can be created by calling its constructor. The class inherits from the QWidget.

lbl = ICTextLabel("Message", "Hello World")
# get the name of the label
print (lbl.name)
# set a new value of the label
lbl.value = str(1.25)

The class exposes several properties to get and set displayed values, its apperance and behaviour. The follwoing properties are exposed

# set new background colors
lbl.back_colors = (QtGui.QColor(200, 200, 200), QtGui.QColor(100, 100, 100)) 

This is used to display the time. The clock label is defined by ICClockLabel. The class inherits ICTextLabel. The .value property of the ICTextLabel class stores the current time. The displayed time is updated using a timer.

clk_lbl = ICClockLabel("Time")
# get current time.
current_time = clk_lbl.time_now

A linear gauge is used to graphically display changing values of parameters. In the animation below, we show its use for tracking pressure. The ICLinearGauge allows definiation of two alarm limits, an upper limit and a lower limit. It also allows tracking of cycle maximum and cycle minimum. This is again a compound widget, which consists of the

• gauge bar defined in the class ICGaugeBar
• a title label at the top, and
• a value label at the bottom

The code below shows creation and manipulation of a linear gauge

# ICLinearGauge(name: str, unit: str, min_val: float, max_val: float, display_steps: int)
# min_val is the minimum value displayed on the bar
# max_val is the maximum value displayed on the bar
gauge = ICLinearGauge("Pressure", "Pa", 0, 120, 6)

# gauge.gauge_bar is of type ICGaugeBar and implements the gauge bar 
gauge.gauge_bar.lower_alarm = ("low", 20)
gauge.gauge_bar.upper_alarm = ("high", 100)

# set the value of the gauge bar
gauge.value = 40

# start cycle max and min tracking 
gauge.gauge_bar.start_max_tracking()
gauge.gauge_bar.start_min_tracking()

The following properties are avaiable from the ICLinearGauge object

The ICLinearGauge object initiates a ICGaugeBar object to represent the gauge bar. The following properties are implemented and can be accessed through the .gauge_bar member. The ICGaugeBar object can also be used independently in a GUI.

Min and max tracking are enabled through fuctions. To track cycle maximum, every cycle the tracking can be reset to restart the tracking.

A value change event is emitted by this class. changed event passes the current value.

Two basic buttons are shown in the figure above. The ICBaseButton class inherits the QWidget class. The puropse of the class is to capture the click events. The button is created by calling

# constructor ICBaseButton(name: str, button_id: int)
but = ICBaseButton("Ok", 0)

The following properties are implemented by the class

The different possible states defined in ICWidgetState are

On clicking the button emits clicked event. The clicked event has two formats

1. If the .button_id is defined then the raised event passes both .name and .button_id with the event
2. If the .button_id is not defined then the raised event passes .name only

# in the user code the event can be captured by connecting to the event
but.clicked.connect(on_ok_click)

# the function to be called in the case of a button click event
@pyqtSlot(str, int)
def on_ok_click(name: str, id: int):
  print("button clicked")

A toggle button is a state maintaining button. They represent the mechanical swithces. One example is an start-stop switch for any instrument. The toggle button class ICToggleButton inherits the ICBaseButton class. The toggle button shows a label on the top left. It is used to indicate what type of parameter is being toggled. The main text in the centre changes with the state. There is a LED button to distinguish the two states as shown in the images below.

The toggle button can be created by

# ICToggleButton(label: str, off_text: str, on_text: str, init_state: bool, led_type: ICLEDType)
btn = ICToggleButton("Operation", "Pause", "Resume", False, ICLEDType.ToggleNormal)

The follwoing properties are available to modify the button behaviour

The toggle button emits the toggled signal. There are two variants

1. If the button id is define then the emitted signal passes .state and .button_id
2. If the button id is not defined then the emitted signal passes the .state of the toggle button.

Alarms and error messages are an integral part of any instrument control panel. This widget provides a simple way of showing alarms and error codes. The widget consists of a text which displays the error message with the time at which the alarm was raised. The widget also incorporates a toggle button to acknowledge and silent the alarma as seen in the image below. In the image below, three alarm widgets have been added in the dialog box.

The alarm widget is created in the activated state

# ICAlarmWidget(alarm_id: int, alarm_message: str, alarm_description: str, led_type: ICLEDType)
alrm1 = ICAlarmWidget(0, "critical alarm", "This is a critical alarm.", ICLEDType.AlarmCritical)

The widget can be manipulated using the following properties exposed by the class

The widget emits the acknowledged event, when the alarm is acknowledged by the user. The event passes the alarm id as its parameter.