Virtual Soldering （2）

Published:2011/8/2 2:39:00 Author:Amy From:SeekIC

Dr. Thomas Scherer

What is LabVIEW?

The first version of LabVIEW (1.0) appeared in 1986, ini­tially only for the Apple Macintosh computer. At that point the Mac itself was already two years old and repre­sented a revolution in user-friendliness in the history of personal computing. Text-based entry was replaced by graphical metaphors, including a desktop with windows, waste basket and mouse. High-resolution bit-mapped dis­plays replaced the chunky graphics we were accustomed to from DOS and its cousins. Nl translated this metaphor into the field of measurement and test.

At that time various computer-controlled instruments had already been available for some time, although they were very expensive. They were based on the GPIB (gen­eral purpose interface bus). The essence of Nl’s idea was to create a graphical programming interface where these instruments were represented by icons. In addition, math­ematical functions, input units (such as switches) and out­put units (such as LEDs or oscilloscope displays) were also represented using graphical symbols. The icons were linked not by a couple of lines of code, but by a kind of ’wire’. Following the metaphor, the corresponding tool is represented in the user interface by a wiring pen, as frequently used in prototyping.

Figure 1 shows the appearance of a very simple arrangement of data source, data processing and data display units, forming a ’wired circuit’. The program does simply this: the input value entered on the control panel (2.5) is multiplied by a factor (2), and the result (5) is dis­played on the scale of a simulated analogue meter. The function is displayed in the diagram using an amplifier symbol with the factor 2 shown. Wires run from the numeric input unit and the constant to the two inputs of a multiplier unil, and from the output of the multiplier to the input of the output unit.



Data and numeric values, rather than currents, flow through these virtual wires, in this example from left lo right. A module or icon executes its function v/hen data are present at all its inputs. The sequence of processing operations is therefore not like that in normal program­ming languages where the flow of the text is followed from top to bottom (except where jumps occur), but depends instead on the flow of data. This is called a data flow driven architecture and gives great flexibility. Nl generally refers lo the individual modules as Virtual Instru­ments (Vis). An important further consequence of the architecture is that a number of independent (that is, not interconnected) Vis can be placed in a diagram and they will be processed in parallel: multitasking is thus a built-in feature of LabVIEW.

Further, it is possible to select either a part or the whole of such a module, along with its wiring, and with the click of the mouse bring it into a new module which can have its own icon. In this way code can be written once and then easily reused. This process is analogous to the organization of code in normal programming languages into functions and procedures. In LabVIEW, by compari­son, things are much more transparent.

From our example we can clearly see that program­ming in this style is the most natural process imagina­ble. It is very similar to drawing a circuit diagram, where the individual Vis represent electronic compo­nents. It is an easy intuitive step to go from constructing electronic circuits to programming in LabVIEW. For classically-trained pro­grammers and computer scientists, on the other hand, accustomed to the tra­ditional methods of writing software, this technology takes some getting used to. A completely new way of thinking is required. Perhaps they would find it worth changing?

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