Dials & Gauges Blockset

Simulating a Multiple-Needle Stopwatch

This example model simulates a typical sailing stopwatch. The model uses the Stop Watch block, which displays three needles on individual angular scales. The needles mark simulation time simultaneously, as follows:

• The large needle spans 1 minute.
• The small needle on the left spans 1 second.
• The small needle on the right spans 15 minutes.

To open this example, enter dng_stopwatch in the MATLAB Command Window. Run the simulation and watch how the three needles move.

These sections describe how the model works:

• How NeedleID Values Correspond to Needles
• Configuration of the Stop Watch Block
• Preparing the Input Signal for the Stop Watch Block

How NeedleID Values Correspond to Needles

To explain how the model controls three needles, this section first explains how the block makes its needles accessible to you. Each needle on the block has an associated pair of NeedleID and Value parameters, where

• NeedleID is a number that distinguishes that needle from other needles on the block.
• Value is the numerical value for that needle along its angular scale.

You can view or control these parameters via the Needles panel of the block's ActiveX Control Properties dialog box.

To find out which needle and range of values correspond to a given ID number, use this procedure:

1. Right-click on the Stop Watch block and choose Control Display Properties.
2. Click on the Needles tab.
3. Set NeedleID to the ID number you want to investigate: 0, 1, or 2 in this case.
4. Change the Value parameter while watching which needle on the block moves. By dragging the Value slider to its extremes, you can also find out the minimum and maximum values for the needle with that NeedleID number.

The table below summarizes what the procedure reveals.

NeedleID	Needle on Block	Range of Values
0	Large needle	[0, 60] seconds
1	Small needle on right	[0, 15] minutes
2	Small needle on left	[0, 5] fifths of a second

For more information about ID properties, see Understanding ID Properties.

Configuration of the Stop Watch Block

After you run the model, the number 6 appears near the connector line that represents the input to the Stop Watch block. This indicates that the signal on that line is a vector of length 6. To understand why, first right-click on the Stop Watch block and choose Block Parameters.

Then notice that the Input property field in the dialog box is set to

• NeedleID,NeedleValue,NeedleID,NeedleValue,NeedleID,NeedleValue
  

By contrast, the default value for this property is NeedleValue, which you can see by examining the block in the Angular Gauges library.

The comma-separated list in this example model causes the Stop Watch block to use the six values in its vector input signal to assign these parameters to the block, in sequence:

• The ID number, 0, of the large needle
• The numerical value for the large needle
• The ID number, 2, of the small needle on the left
• The numerical value for the small needle on the left
• The ID number, 1, of the small needle on the right
• The numerical value for the small needle on the right

Note    It is important that each needle's ID number precede its numerical value. Referring first to the ID number tells the block which needle to apply changes to.

Preparing the Input Signal for the Stop Watch Block

The model aims to reflect the time on the Stop Watch block. However, it is necessary to process the Clock block's output somewhat to prepare it for the Stop Watch block. Double-click on the Subsystem block to open it. The subsystem accomplishes two key tasks:

• Processing the Clock block's output value, measured in seconds, to make it an appropriate numerical value for each needle. To do this, the block performs these computations:
• Reduces modulo 60, to get the large needle's value.
• Reduces modulo 1 and then multiplies by 5, to get the left needle's value. Recall that values for the left needle range between 0 and 5.
• Reduces modulo 15*60 and then divides by 60, to get the right needle's value. Recall that values for the right needle range between 0 and 15.
• Forming a six-element vector corresponding to the comma-separated list in Configuration of the Stop Watch Block. To form this vector, the subsystem uses three Constant blocks, the three processed Clock block signals, and a Mux block.

  

Controlling Multiple Graphical Elements

Updating Multiple Portions of a Pie Chart