Shift Register: Exercise # 1: Shift Register Example VI. 1. Build the following front panel. Figure (8.1): Shift register exercise front panel

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1 Experiment # 8: Shift Register and arrays Shift Register: Use shift register on for loops and while loops to transfer values from one loop to the next, create a shift register by right clicking the left or right border of a loop and selecting add shift register from the shortcut menu. You can use shift register to remember values from previous iterations. This technique is useful for averaging data points. To configure a shift register to carry more than one value to the next iteration, right click the left terminal and select add element from the shortcut menu. To initialize a shift register, wire any value from outside the loop to the left terminal. If you don't initialize the register, the loop uses the value written to the register when the loop last executed or the default value for the data type if the loop has never executed. For example, if the shift register data type is Boolean, the initial value is false. Similarly, if the shift register data type is numeric, the initial value is 0. Exercise # 1: Shift Register Example VI. 1. Build the following front panel. 2. Display the following block diagram: Figure (8.1): Shift register exercise front panel Figure (8.2): Shift register exercise block diagram 1

2 * The Xi indicator displays the current value), which shifts to the left terminal at the beginning of the next iteration. The X (i-1) indicator displays the value one iteration ago, the X (i-2) indicator displays the value two iterations ago, and so on. * The 0 wired to the left terminal initializes the elements of the shift register to 0. * Click the highlight Execution button to enable execution step by step. *In each iteration of the while loop, the VI transfers the previous values through the left terminals of the shift register. Each iteration of the loop adds 5 to the current data, Xi.this value shifts to the left terminal, X (i-1), at the beginning of the next iteration. The values at the left terminal tunnel downward through the terminals. This VI retains the last three values. *The output of the first iteration is: Xi=5,X(i-1) =0,X(i-2) =0,X(i-3) =0.The second iteration is: Xi=10,X(i-1) =5,X(i-2) =0,X(i-3) =0 and so on. Exercise # 2: Temperature running Average VI. Complete the following steps to modify the temperature monitor VI (exercise#3 in exp# 8) to average the last three temperature measurements and display the average on a waveform chart. 1. Front Panel: open the temperature monitor VI you built in exercise 3, exp#8. 2. Display the block diagram. 3. Right click the left or right border of the while loop and select add shift register. 4. Right click the left terminal of the shift register and select add element. 5. modify the block diagram as follows: Figure (8.3): Temp running average block diagram 2

3 The thermometer VI (inside the loop) returns one temperature measurement every second and the outside one initializes the left shift registers before the loop starts. The compound arithmetic function returns the sum of the current temp X(i) and the two previous temp readings X(i-1) and X(i-2). Divide function returns the average of the last three temp readings (current value X(i), one iteration ago value X(i-1)and two iteration ago value X(i-2)). *Run the VI, during each iteration of the while loop, the thermometer VI takes one temperature measurement. The VI adds this value to the last two measurements stored in the left terminals of the shift register, the VI divides the result by three to find the average of the three measurements. Case structure: A case structure has two or more sub diagrams or cases. Only one sub diagram is visible at a time. And the structure executes only one case at a time. An input value determines which sub diagram executes. The case selector identifier at the top of the case structure contains the case selector identifier in the center and decrement and increment arrow buttons on each side. Use the decrement and increment arrow buttons to scroll through the available cases. Wire an input value or selector to the selector terminal to determine which case executes. You can wire an integer, Boolean value or string. If the selector terminal is Boolean, the structure has a TRUE case and a FALSE case. *Right click the case structure border to add duplicate, remove or rearrange cases and to select a default case (you must specify a default case). Exercise #3: Boolean Case Structure. In the following example, the numbers a and b are either added or subtracted depending on the value wired to the selector terminal. 3

4 Figure (8.4): Boolean Case Structures If the Boolean control wired to the selector terminal is true, the VI adds the numbers, otherwise the VI subtracts the numbers. 4

5 Arrays: Arrays group data elements of the same type. An array consists of elements and dimensions. Elements are the data that make up the array; a dimension is the length, height or depth of an array. An array can have one or more dimensions. An array uses an index so you can readily access any particular element. The index is zero based, which means it is in the range 0 to n-1.where n is the number of elements in the array. *Creating 1D array of random numbers (0-1). Front Panel: Select an array on the controls>>arrays and cluster palette, place it on the front panel and drag a control or indicator into the array shell. Figure (8.5): 1D array front panel Block diagram: Build the following block diagram Figure (8.6): 1D array block diagram 2D array stores elements in a grid, it requires a column index and a row index to locate an element, both of which are zero based. 5

6 0 1 Row Index 2 3 Column Index To add dimension to an array one at a time, right click the index display and select add dimension. Auto-indexing: If you wire an array to a for loop or while loop input tunnel, you can read and process every element in that array by enabling auto indexing. When you auto index an array output tunnel, the output array receives a new element from every iteration of the loop. Disable auto indexing by right clicking the tunnel and selecting disable indexing from the shortcut menu. For example, disable auto indexing if you need only the last value Passed to the tunnel. *Creating 2D arrays of random numbers (0-1): You can use two for loops, one inside the other to create a 2D array. The outer loop creates the row elements and the inner loop creates the column elements. Exercise #4: Array functions. Figure (8.7): 2D array examples Build a VI that first accumulates an array of temperature values using the digital thermometer VI. Incorporate these items: * Set the array size with a control on the front panel. * Initialize an array using the initialize array function of the same size where all values are equal to 10. * add the two arrays, calculate the size of the final array and extract the middle value from the final array. * display the temperature array, initialized array, final array and mid value. 6

7 Exercise #5: Build a VI that measures temperature every 0.25s for 10s, during the acquisition, the VI displays the measurements on a waveform chart. After the acquisition is complete the VI plots the data on a graph and calculates the minimum, maximum and average temperatures. 7

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