Tutorial guide to using a spreadsheet to graph data

Transcription

1 Tutorial guide to using a spreadsheet to graph data Preamble: This appendix is meant to be a guide, not a set of rigid instructions. Follow it, and you will get a result, but feel free to deviate from the instructions and experiment. There is no single correct method for producing a graph, and no one correct graph. If you are stuck, please ask. 1 Spreadsheet overview The Spreadsheet is a calculating tool which can used for manipulation of numerical data. Spreadsheet tools are available from various different sources: Excel from Microsoft, StarOffice from Sun, OpenOfice from OpenOffice.org. In this lab we will use OpenOffice. If you are familiar with using Excel then you will notice only minor differences. Possible uses for spreadsheets range from scientific and statistical work to financial planning. It normally consits of a table of cells, arranged in rows and columns. After information is inserted into the rows and columns of a spreadsheet, one can: Insert formulae so that the spreadsheet performs calculations. Display information by making and printing charts and graphs. Change the appearance of the spreadsheet and charts/graphs. A spreadsheet is created by typing information into cells: the rows and columns intersect to form cells. The information can be text, numbers, dates, or time. When the data has been entered, formulae which use the entered data can be entered into further cells. Once a formula is entered, you can change the information in the cells it refers to and the formula will automatically recalculate the numbers and give you a new value. 2 How to enter experimental data and create a graph. 1 Start the spreadsheet Details of how to do this will be given in the Lab but generally the spreadsheet can be accessed either from an icon in a desktop folder (e.g., EE2) or e.g., from: Start -> All Programs -> Spreadsheets -> OpenOffice.org Calc This will open up the Open Office desktop. This will open an empty spreadsheet for you to work with. Electronics 2 Project Laboratory 1

2 2 Type in your data, headings, name, date, title, etc Type in all data and labels, and formulae to make the spreadsheet look something like this: The entries are typed into each cell. Where there is a repeated value (e.g., the column Vin) edit -> fill -> down can be used to avoid repetitious typing. Experiment with this, so you know how to do it. 3 Formulae The Gain and Gain in db can be calculated for you, by using formulae. Formulae have the following structure (e.g): =D6/C6 =LOG10(E6) =20*F1 =2*PI*B1 In formulae, you reference numbers in other cells of the spreadsheet (e.g. C6), and manipulate those values (with either constants, other cell values, or built-in formulae) to create new values. Spreadsheets have many built-in functions. Electronics 2 Project Laboratory 2

3 The following may be useful: * / + - ^ COS(x) EXP(x) INT(x) LN(x) LOG10(x) PI() SIN(x) SQRT(x) TAN(x) To find more about functions you can use the search tool from the Help icon in the Main Toolbar. 4 Creating regular repetitions Once you have entered the formula, click the cell to select it and place the cursor over the lower right corner so it changes in to a plus sign, in this position click and drag down the column. This will auto repeat the regular pattern of formulae, and save you typing the similar formulae repeatedly. 3 Graphing your results 1 Create a new graph (or chart) To graph your data, use the mouse to select all of the frequency values, in their column, including the title. Then hold down the control key on the keyboard and select all the Gain (in db) values, in their column, including the title (by dragging the mouse, with the L.H. button held down). From the main toolbar, select: Insert -> Chart This will display the AutoFormat Chart window. Click the button marked: Next >> Electronics 2 Project Laboratory 3

4 2 Make the chart a scatter plot. You will now see a dialog box like this: Select the XY chart ( icon, in the 2 nd row, 2 nd column) and click Next>>. This will display the following window: Select the lines with symbols variant (2 nd entry) and Next>> button. Electronics 2 Project Laboratory 4

5 3 Label the axes and give the graph a title The next window gives you the option to define titles for the chart. Remember any graph must have a definition of what each axis represents and the units used. Select the Chart Title and Axis Title check boxes and enter suitable captions. Then click the Create button. This will create the chart and display it on the spreadsheet. 4 Modify the X-axis scale To get the correct Bode Plot shape both the y-axis and x-axis data need to be represented as logarithms. For the y-axis data this happens because of the LOG10 function. For the x-axis we need to do this by choosing the graph x-axis scale to be logarithmic, as follows: Double click the horizontal axis on the graph. This should open the following window: Electronics 2 Project Laboratory 5

6 Select the Logarithmic scale check box and click OK. Your graph should look something like this: 5 Print you graph, and save your work. It is important to save your data, and to print your graph. Both will be an important part of your final project report. ALWAYS KEEP YOUR WORK ON YOUR SMS ACCOUNT. Electronics 2 Project Laboratory 6