excel by example a microsoft excel cookbook for electronics engineers phần 5 pot

Example 8: Resistor Color Code Decoder Using Speech InputFigure 8-7: Creating a customized toolbar.. Figure 8-10: The Resistor toolbar... Example 8: Resistor Color Code Decoder Using Spe

Example 8: Resistor Color Code Decoder Using Speech Input

Figure 8-7: Creating a customized toolbar.

Figure 8-8: Placing a button on the new toolbar.

Right-click on this smiley and on the pop-up menu (Figure 8-9), change the Name to

Commence, select Text Only (Always), and Assign Macro assigning the button to the

macro of the same name Irritatingly, this process may take several right-clicks

Figure 8-9: Changing button properties.

We repeat the process for all the colors and the Backup macros until we are left with a bar that looks like Figure 8-10

tool-Clicking on any one of the buttons should run the macro updating the bands on the resistor

We can get rid of the toolbar by clicking the “X” on the top right-hand corner, and make

it reappear (or disappear) by right-clicking on a toolbar and selecting (or deselecting) the

Resistor option Of course, it is possible to delete entirely by going into Tools | Customize

| Resistor | Delete but I don’t think we should do that just yet.

In Parenthesis: Exporting a Toolbar

Toolbars are normally associated with an Excel installation They can be inserted into

a workbook for transportation, which is what I hope will happen with this example In the customize dialog (Figure 8-7) having selected the Toolbars tab, click on the Attach

button In the next dialog box that appears, select the desired toolbar (in the “Custom Toolbars” panel) and click on the Copy>> button between the panels The toolbar should

be copied to the “Toolbars in Workbook” panel Click on OK.

Figure 8-10: The Resistor toolbar.

Example 8: Resistor Color Code Decoder Using Speech Input

Adding Speech

We now re-enable the Language toolbar using the menu selections Tools | Speech | Speech Recognition Ensure that the microphone is in the record state (also the mute button on the actual microphone, if there is one), click on the Voice Command button and then on the Tools button On the drop-down menu, select Add/Delete Words and you will be presented

with the dialog box of Figure 8-11 For each voice command that we are going to use, type

the command word (like “Commence” or “Red”) in the “Word” box, click on Record nunciation, and annunciate the word The software then adds the word to the dictionary

pro-It is more reliable to record the exact word to associate with the macro than to rely on the speech recognition algorithm to recognize a word by application of rules

Figure 8-11: Adding specific words to the word recognition database.

When all fifteen words (including Evaluate) have been added, close the box It is time to try out how this works Ensure that the Voice Command button is clicked on the Language toolbar and that the microphone is enabled Now say the words and the macro should be executed Simple enough!

By the way, as suggested by the Speech Recognition documentation, a good microphone ally does improve the performance

re-Evaluate the Color Code

The Evaluate function is far too lengthy to produce here in its entirety It evaluates a different set of circumstances for each number of bands An excerpt for the 4-band case is shown here:

Case 4

‘4 bands

nLegalValue = 0

‘preset value to indicate that the output is legal

‘if set to 1 then this is an illegal value

‘any other value

nForward = nForward * 10 ^ Range(“h7”).Value

‘now for the tolerance

Select Case Range(“j7”).Value

Case 11:

Example 8: Resistor Color Code Decoder Using Speech Input

‘any other value

nForward = nForward * 10 ^ Range(“f7”).Value

‘now for the tolerance

Select Case Range(“d7”).Value

Example 8: Resistor Color Code Decoder Using Speech Input

Since sometimes it is hard to figure out which is the first band and which is the last, the tine also reverses the process and evaluates the bands from right to left

rou-The results are saved in two cells reserved for the forward and the reverse readings

Obviously, the interpretation of five- and six-band resistors has a few more lines of code and uses a different series of resistor values, but in principle, they work exactly in the same way

Of some note in the software is the “exit for” statement Those of you with “C” experience will know this as the “break” statement used with a “for” loop in order to break out of the loop This is also the first time in this book we have used our own function call A function only differs from a procedure in that it returns a value

Now that the Evaluate macro is complete, we must add the button to the Resistor toolbar in

exactly the same way as before using the Tools | Customize | Commands tab & Macro

se-quence, dragging the button to the toolbar and then changing the name and associating the macro (There is a drop-down button on the Resistor toolbar that allows you to add a button instead of the above technique It was possibly finger problems on my part, but I could not get this approach to work with speech recognition.)

Now we are almost ready to roll You can try it out and see how it works Obviously you don’t need to use speech recognition; you can simply click on the toolbar buttons The toolbar must be visible in order for the speech recognition to work

Text to Speech

Not only do you get to talk to your computer, you can get your computer to talk back to you You can change the properties of the speaking voice and the output device from the Speech

icon in the Window Control Panel Click on the Text to speech tab Once this has been set

to your satisfaction, return to the workbook

Enable the Text To Speech toolbar by following the menus Tools | Speech | Show Text To Speech toolbar Click on the By Rows button (as seen from the pop-up description) on the

toolbar Then block cells A15 to C16 and click on the Speak Cells button The four cells

should be read back to you

It is simple enough to record this process to a macro called Speak, and the call to it is tucked

in as the last thing to do in the Evaluate function The only problem is that the Text to Speech function changes the active cell and that plays havoc with the backup function We need to insert a method to record the current location and then restore it after the “Speak” procedure We can do that using the following sequence:

espe-R T = R 0 + α R 0 [T – δ(T/100 – 1) –β (T/100 – 1)(T 3 /100)]

But normally, only the α coefficient is given and lookup tables are provided From this tion it is obvious that the relationship between resistance and temperature is nonlinear.One of the most common RTD types is made with platinum wire, with an α of 0.00385, which has a resistance of 100Ω at 0°C RTDs are available in 2-, 3- and 4-wire types The additional wires are used to null the effect of the resistance of the wires connecting the RTD

equa-to the electronics

As discussed in an earlier example, the 4–20 mA current loop is very popular as a means of transmitting an analog signal around a factory floor because of its high noise immunity to electrically induced noise and its ability to power the sensor (hence the 4 mA offset) while measuring the signal At the bottom end of the input range, the current through the loop driver is controlled to 4 mA, and it will increase to 20 mA at full scale input

The RTD and current loop are so common that Texas Instruments/Burr-Brown manufacture

an integrated circuit (XTR105) that does the conversion A basic circuit can be seen in Figure 9-1

The XTR105 provides two identical current sources to drive the RTD and a reference tor RZ The difference in voltages developed by these currents is amplified and conditioned

resis-to generate the 16 mA range at the output At the minimum input temperature RZ should

be equal to the RTD value so that the input voltage differential is zero The upper value

RTD to 4–20 mA Converter:

XTR105

is determined by the gain resistor RG, and the XTR105 also has the ability to linearize the output with the addition of another resistor, RLIN1.

The relationship between the resistor values is as follows:

RLIN = 1KΩ (internal to the XTR105)

Assuming we make this as a product where a customer can order any input temperature range, it would make an ideal model to implement in Excel

Acquiring RTD Tables

The first step is to generate the RTD tables in Excel After a search on the Internet, I cessed a table in HTML format from www.instrumentation.com (named for the company) for

ac-a plac-atinum RTD, in degrees Celsius In the browser, I selected Edit | Select All ac-and copied

the selection into a Wordpad file, where I gently massaged it and saved it as a text file which

is on the CD-ROM as table.txt An extract follows:

I 4–20mAO

Example 9: RTD to 4-20 mA Converter: XTR105

In order to get this into Excel, we follow the menu sequence Data | Import External Data | Import Data, and browse and select the “table.txt” file We will be faced with Figure 9-2.

Figure 9-2: Importing a text file.

Ensure that the Delimited radio button is selected and click on Next, proceeding to Figure 9-3.

Figure 9-3: Setting delimiters.

Make sure the Space option is checked as a delimiter and click on Finish The data will

ap-pear as in Figure 9-4

Figure 9-4: RTD data loaded.

Note that for negative temperatures, the change in the values from left to right corresponds

to the increase in the absolute value of the temperature and is inconsistent with the data presented for temperatures above zero in terms of a software lookup approach I looked at tables provided by several RTD suppliers and quite a few seemed to use this approach It is easy enough to use Excel to manipulate the data into a form that we need Initially we need

to mirror the data, so in cell N4 I entered the formula:

Figure 9-6 shows the results to date For the same selection, we cut (<Ctrl> + <X>) and

paste it into the range B4 to L23 overwriting the original order We block A3 to A22, cut it and shift it down a row We delete the last two columns (L and M), add a little formatting and we are left with Figure 9-7

Figure 9-7: Completed RTD table.

Lookup RTD Value

The INDEX function has the format:

INDEX(array,row_num,column_num)

We have to manipulate the temperature to locate the correct row and column number First,

we enter any temperature in cell N1, just to start the process off Let’s use 125

The rows increment by ten degrees, so we need to find the row based on the number of tens

in the temperature To do this we use the INT function In cell N3, we enter:

=INT(N1/10)

and this returns a number of 12 The columns are based on the remainder of the above sion In cell O3 we enter:

divi-=MOD(N1,10)

Example 9: RTD to 4-20 mA Converter: XTR105

and it returns 5 We still need to do some manipulation of this First, the table starts at –200°C, so we need to add a (200/10) for the offset and also the table (we will define later) starts at cell B4 For the INDEX function, row 1 column 1 defines cell B4, so we need to add

a 1 to the 20 on the row offset and a 1 to the column offset to align the lookup action with the actual table

If we put it all together, we enter in cell N5:

Go to the VBA editor (Macro | Visual Basic Editor or <Alt> + <F11>) Insert a module

(Insert | Module) Change the name of the Project to RTDproject, and the name of the

module to RTDmodule in the module properties window We need to do this because when

this function is accessed from another workbook, the name must be unique or there may be

a conflict In the code window for the RTDmodule, add the code as shown below The result appears in Figure 9-8

Function RTDvalue(nTemperature As Integer) As Variant

Dim nItermediate As Variant

Dim nItermediate2 As Variant

The first part of the code recreates the Excel MOD function The VBA Mod instruction does not perform in the same way and since they are named the same you cannot access the Excel function in this case But VBA can access the Excel INDEX function using the Application.WorksheetFunction construct.

Figure 9-8: Function to lookup the RTD resistance.

Example 9: RTD to 4-20 mA Converter: XTR105

Using the expand button, it is possible to actually click on the actual cell needed for the

argument of the function, and click on OK The cell now should have the same value as cell

N5, which was calculated directly in Excel Changing the temperature in N1 should lead to both cells N5 and N7 updating and showing the same value Notice that there is a preview

of the result in the lower part of Figure 9-10

It is possible to avoid this Insert Function utility by simply entering the formula in F7:

=RTDvalue(N1)

Figure 9-9: Insert a function.

Figure 9-10: Selecting the input range.

Adding a Help Description to a Function

In Figure 9-9 and Figure 9-10, the comment “No help available” can be changed to provide

something more informative In the RTD workbook, go through the menus Tools | Macros

| Macros (or <Alt> + <F8>) Only procedures will be found automatically, so we enter the

name RTDvalue manually We then click on the Options button and add descriptive text as

in Figure 9-11 Click on OK and then Cancel.

Figure 9-11: Adding a help description to a function.

Creating the Model in Excel

Open a new workbook and name it XTR105.xls using the File | Save as sequence Open

the VBA editor (<Alt> + <F11> or use the menus) In VBA, select Tools | References | Browse and select type of files to *.xls Search for and select the “RTD.xls” files (Figure 9-12) and click on Open, followed by Enter

We only need to do this if the worksheet containing the function (RTD.xls) is not open Nevertheless, this will open the worksheet since we require the worksheet to be open in one form or another during regular operation

Return to the new workbook and prepare the initial data, naming cells D4 to D7 for the descriptions in A4 to A7

Example 9: RTD to 4-20 mA Converter: XTR105

Figure 9-13 shows the formulas that are entered to calculate the resistor values (done by

selecting the Formulas option in the Tools | Options | View sequence) The CONVERT

function can be used to convert between many different kinds of units

Figure 9-12: Finding a function in another workbook.

Figure 9-13: Formulas behind the worksheet of Figure 9-14.

Example 9: RTD to 4-20 mA Converter: XTR105

Figure 9-14 is the actual worksheet with the resistor results shown The user is expected to choose Fahrenheit or Celsius, and the minimum and maximum temperature The resultant values of RZ, RG and RLIN1 are produced in response to these inputs

Figure 9-14: Initial worksheet.

Standard Resistor Values

Of course, you all know what the next step is going to be! Resistors are only made in crete values and so we would like to know what values to use Let’s put the current project

dis-on hold while we investigate a new workbook (NearestValue.xls) that will allow us to look

up the nearest resistor values The functions return a numeric value rather than text so that they can be used directly in calculations This is an interesting workbook since it does not need any entries on any of the sheets It is purely an exercise in VBA programming The four functions provided in the workbook allow for selection of resistors in the A (NearestValueA) and B (NearestValueB) series of values, for potentiometers (NearestPot), and a procedure that converts a number to the normal way of expressing the resistor value (LookupStan-dardResB)

By the way, if you don’t want to get into the programming, the four functions can be accessed

by simply using the module as an “add-in.” You should then skip to the section titled, ing the NearestValues Add-In.

Install-There are several ways of generating a standard value for a given resistor value The nique I adopted in the end, while it is a “brute force” approach, allows for simple expansion for other types of devices

tech-The code is too large to reproduce here, and anyway you have the source code on the CD, so

I will show a snippet or two in order to elucidate

The initial part of the function “NearestResistorA” defines the variables used I found that

I needed the double precision to prevent rounding errors in the value returned The value

under consideration, provided as an argument to the function, is called CalculatedValue The

first step in the process is to consider that the CalculatedValue must be greater than 1 Ω and less than 10 MΩ If the value is outside this range, an error value is returned In order for other Excel functions to interpret this as an error, the CVErr function must be invoked