Setting Switch And Permanent Connection Resistance

No measurement equipment is 100% accurate. When setting properties for switches and permanent connections it's important to keep the specifications of the Mistral in mind to insure the keypad meets your requirements. Several examples will help illustrate the point.

Say you have a keypad with a switch whose resistance must be 50 Ohms or less. If you set the switch item in your Keypad File to have a Max Res of 50 Ohms and a Min Res of 0 you may pass keypads that are bad and fail keypads that are good. For resistances less than 100 Ohms the Mistral has an accuracy of +/- 2 Ohms. This means a switch whose real value is 49 Ohms could be measured by the Mistral as 51 Ohms and failed. Or a switch that is really 51 Ohms could be measured as 49 Ohms by the Mistral and considered good. To be absolutely certain that only switches with a resistance of 50 Ohms or less are passed, set the Max Res property of the switch to 48 Ohms. Note that there is a chance this may result in some parts that are actually good being failed, but you will know that all the parts that passed are definitely good.

Mistral specifications are also important when measuring resistors. Assume you have a keypad with a 2.0k Ohm, 5% resistor. For resistances between 100 Ohms and 50k Ohms the Mistral has an accuracy of +/-2%. In order to insure that the resistor on the keypad is within tolerance you need to create a permanent connection with a resistance of 2.0k Ohms, +/-3%. Again, this may result in good parts being failed but you will be sure that all the parts that passed are good.

See Specifications for complete Mistral accuracy information.

Testing Duplicate Switches

In some cases your keypad may contain two or more switches that connect the same two pins. To test these switches properly you will need to take some extra steps.

Start by creating a new file. When the Edit Info window opens go to the Testing tab and check "Switches must be pressed in sequence". Click "Save" to close the window.

Connect a good keypad to the Mistral and begin learning the keypad automatically (See Learning A Keypad File Automatically for more information about how learning works). When prompted, press the first switch you would like the operator to check when testing keypads. When the switch item pops up in the window, click on it. You should immediately give the switch a name (if you click on an item and just start typing the Label will be edited in the Item Properties). After you name the item, use the mouse to place it on the screen in a location that matches where it is on the keypad.

Continue pressing new switches and naming and placing the items as they pop up. You should press the switches in the order you want the operator to test them. At some point you will press a new switch but instead of a new item popping up, a dialog box will appear telling you that there is already a switch that connects the pins and asking if you want to create another switch item. The reason this happened is that the two switches connect the same two pins. Click on "Yes" and a new switch will be created. Make sure you give it a name and place it on the screen in a location that matches where it is on the keypad so you know which switch it represents. Repeat this process until you've pressed all the switches and then click the "Stop Learning" button.

Note that software versions prior to V3.1.2 behave differently than described above. Please see the Help that came with that software to see how to create duplicate switches.

When testing with the file you've just created, the operator will need to press the switches in order. The switch item for the next switch to press will flash. You can view the order they will need to be pressed by selecting "Show Test Sequence" from the "File" menu. A number will appear in the upper right corner of each switch and LED item indicating its Test Sequence. You can change the order using the Set Test Sequence tool.

The Keypad File is now complete. When testing it is the responsibility of the operator to press the switch that corresponds to the switch item flashing on the screen. If the operator presses another switch that connects the same two pins, the Mistral has no way of detecting that the wrong switch was pressed.

Testing Multi-Pole Switches

We're defining a multi-pole switch as a single switch that connects more than two pins together when pressed. Since the idea behind multi-pole switches is to reduce the number of pins on the keypad, they usually make use of duplicate switches. You might find it helpful to read the above section that describes how to create Keypad Files with duplicate switches before proceeding.

For the purposes of this discussion we'll assume that we want to test a keypad that contains only "3-pole" switches, that is switches that connect three pins together when pressed. The Mistral is capable of testing keypads that contain a mix of switch types, LED's, Permanent Connections, etc. as well as switches that connect more than three pins when pressed.

A 3-pole switch creates three electrical paths. For example if the switch connects pins 1, 2 and 3 then there are paths from 1 to 2, 1 to 3 and 2 to 3 when the switch is pressed. Each path is represented in the Keypad File by a switch item so it takes three switch items to define a 3-pole switch. Note that it would take six switch items to define a 4-pole switch and ten items for a 5-pole switch.

Start by creating a new file. When the Edit Info window opens go to the Testing tab and check "Switches must be pressed in sequence". This option is required for testing multi-pole switches. Click "Save" to close the window.

To save space in the window you may want to set the switch item size to medium or small. To set the size of switches that will be added, use the right mouse button to click on the switch tool and select the size from the pop up menu. You can use extra small but it is difficult to see the Test Sequence numbers which we will be referring to later.

Connect a known good keypad to the Mistral and begin learning the keypad automatically (See Learning A Keypad File Automatically for more information about how learning works). When prompted, press the first switch. When the switch items pop up in the window, click on them. You should immediately give the switches names (if you click on an item and just start typing the Label will be edited in the Item Properties). After you name the items, use the mouse to place them on the screen in a location that matches where it is on the keypad. For example if you have a switch called "Power" you may want to name the three switch items for it "Power 1", "Power 2" and "Power 3" and arrange them into a small triangle.

For a 3-pole switch you should get three new switch items for the first switch you press. If you don't get all three items, press the switch again. The items you've already added will turn yellow and any new items will be gray. Click on the new items and name them.

Continue pressing new switches and naming and placing the items as they pop up. At some point you will press a new switch but instead of three new items popping up, one or more of the items already in the window will turn yellow indicating the switch is down. The reason this happened is that the two switches connect the same two pins. Make a note of which switch you pressed and the name or names of all the corresponding switch items that turned yellow. Repeat this process until you've pressed all the switches and then click the "Stop Learning" button.

You will now need to manually add a switch item for each of the items that just turned yellow when a new switch was pressed. So if when you pressed a new switch, two existing switch items turned yellow and one new one popped up you will need to add two new switch items with the same pin numbers as the two items that turned yellow.

To manually add a switch, click and drag the switch tool onto the window. Now, referring to your notes, click on the item that turned yellow when you pressed the switch you want to complete. Make a note of its pin numbers (they're shown in the Item Properties in the lower left corner). Now click on the new, grey item you created. Change the pin numbers (they're both initially "0") to the numbers from the other switch item. You now have two switch items with the same pin numbers. Repeat this for each switch you pressed during learning that turned another item yellow. After you have the three switch items for each switch, make sure you name each item and place them together on the screen so you can keep track of them.

Now you need to define the sets of three switch items as a single, physical switch. To do this we'll put the switch's items into a "Group". A Group is defined as a number of items that have the same Test Sequence number. The easiest way to create Groups is to use the Set Test Sequence tool. Click on the tool and then click "Yes" when asked if you want to proceed. Now click on one of the items for the first switch you want the operator to press when testing. The number "1" will appear in the upper right corner of the item. Now hold down the shift key while clicking on the other two items for the first switch. The will also get a "1" in the upper right corner. Next, release the shift key and click on a switch item for the second switch you want the operator to press when testing. A "2" will appear in the upper right corner. Again hold down the shift key and click on the other two items for that switch. Continue until all the switch items have been given a Test Sequence number and then click the "Stop Set Sequence" button.

There is another way to define Groups but this method doesn't easily allow you to set the order the switches will be tested. In the edit mode select three items that make up one of the switches. You can select multiple items either by clicking on the first one and then holding the shift key down while clicking on the other items or by clicking and holding the mouse button down while dragging the select rectangle over the items you want to select. Then pick "Group" from the "Edit" menu. You'll notice that the Test Sequence numbers now appear in all the switches (and LED's if there are any) in the upper right corner of each item. You'll also notice that for the Group of three items you have selected, the number is the same. This indicates that these items will be treated as one by the Mistral. Continue Grouping until all the switches are done.

The Keypad File is now complete. When testing the Mistral will make sure that all three electrical paths that make up the switch are good when a switch is pressed. If the items remain red after the switch is release place the mouse over each item and the tool tip will pop up indicating what's wrong. It is the responsibility of the operator to press the switch that corresponds to the switch items flashing on the screen. If the operator presses another switch that connects the same two pins, the Mistral has no way of detecting that the wrong switch was pressed.

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