Lab 6. Simon Says

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Lab 6: Simon Says—16 Push-Button Matrix Keyboard

Introduction Have you ever played the electronic version of Simon Says? A sequence of varied color lights in a 4 x 4 grid flash on one at a time. The game is to memorize the sequence and push switches in a 4 x 4 matrix in the same pattern. Each time the sequence is mastered, the sequence becomes longer.

Fig. 1 Simon Says Display

Purpose This lab shows how to use the myDAQ 8-bit port to read 16 switches arranged in a 4 x 4 matrix (Fig. 1). A LabVIEW program converts the switch pressed into a byte containing the row and column address. This byte is then converted into a 4-bit binary encoded nybble, which in turn is converted into a single ‘LED’ indicator in the same position as the switch.

Equipment NI myDAQ 4 x 4 Matrix Keypad Solderless Breadboard

Prerequisite Reference Materials NI ELVISmx Digital Reader (DigIn):

http://decibel.ni.com/content/docs/DOC-12944

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NI ELVISmx Digital Writer (DigOut): http://decibel.ni.com/content/docs/DOC-12945

______________________________________________________________________ Exercise 6-1: Getting Started

The first step is to make an interface between the matrix switch and the myDAQ 8-bit port. A 4 x 4 matrix switch places the switches into a square arrangement with four lines to address the rows and four lines to address the columns (Fig. 2).

Fig. 2 Schematic Diagram and Picture of a 4 x 4 Matrix Switch When you press on a switch position, a row address line is connected to a column address line. There is a unique address for each switch. Connect the row lines to myDAQ bits (0-3). Connect the column lines to myDAQ bits (4-7).

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From the NI ELVISmx Instrument Launcher strip, select DigOut, as shown in Fig. 3.

Fig. 3 NI ELVISmx Digital Writer Instrument Panel Select (0 - 3) in the [Lines To Write] box. Select (Manual) in the [Pattern] box. The [Run] button will output the pattern set on Lines: (3,2,1,0) to the lower nybble on the myDAQ port and hence activate the row address. HI corresponds to +4 volts and LO corresponds to 0 volts. From the NI ELVISmx Instrument Launcher strip, select DigIn, as shown in Fig. 4. Select (4 - 7) in the [Lines to Read] box. Pressing [Run] will read the pattern on myDAQ port bits (7, 6, 5, and 4) and hence will read the column address lines.

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Fig. 4 NI ELVISmx Digital Reader Instrument Panel [Run] both instruments and explore the interaction between the writer bit signals and the read bit signals. This is a simple method to determine the row and column addresses of the matrix switch. Note: Verifying the data sheet for the keypad is crucial, as different manufacturers may use different pin assignments.

Exercise 6-2: Scanning a Keyboard

For our 4 x 4 matrix switch to function properly, one row address is output at a time. After each row is activated, the digital reader gets the response from the myDAQ port (column address lines):

If no switch on the activated line is pressed, the response nybble would read (0000).

If one of the switches is pressed on the activated line, then the response would read (0001), or (0010), or (0100), or (1000). These codes correspond to switches 1, 2, 3, or 4.

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The next row activated corresponds to switches 5, 6, 7, or 8. The following row corresponds to switches 9, A, B, or C. And the final row codes correspond to switches D, *, #, or 0. Note: Different matrix keyboards may have different characters. The column value of a switch pressed is

{0001} = 1 then add 0 to the response number if row 1 {0010} = 2 then add 4 to the response number if row 2 {0100} = 3 then add 8 to the response number if row 3 {1000} = 4 then add 12 to the response number if row 4

Example: If the row code is {0100} and the column code is (0100), then switch 11 has been pressed. In Fig. 2, switch 11 is key [B].

Note: If no switch has been pressed, the column code is (0000). LabVIEW Scanning Program Open the LabVIEW program entitled Scanning.vi. Look at the block diagram in Fig. 5 (Windows/Show Block Diagram). A row activation and column response in the sequence structure is repeated over and over in the while…loop until a key is pressed. This stops the while…loop and displays the 4-bit row address, the 4-bit column address, and a [Key Pressed] flag on the front panel.

Fig. 5 LabVIEW Program to Scan the Matrix Switch for a Key Press and Deliver the Row and Column Address in a Boolean Array

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How It Works The scanning program is contained within a while…loop, which repeats until a key is pressed. The first row code is entered into the sequence structure. The first frame sends the row code via the DAQ Assistant configured to write bits (0-3) to the port. In the next frame, a second DAQ Assistant is configured to read the column states bits (4-7) from the port. These bits are now tested for a key press. Anytime a switch is pressed, a non-zero value for the column address is read. The value of the column nybble is tested with a LabVIEW compare (Not Zero |#0>). This generates a (True/False) flag, which signals a keypress:

If Key press = 1, then stop scanning and record the row and column address.

If Key press = 0, then continue scanning.

When no key is pressed, the row code is rotated to the next row (Rotate) and is used in the next iteration. This process repeats until a key is pressed. Returned from the program is the row address, the column address, and the key-pressed flag. Encoder The Data from the scanning program is passed to a LabVIEW program entitled Encoder.vi, which converts the row and column address nybbles into a single binary encoded nybble. Recall from Lab 5, a nybble has sixteen possible combinations (0 to 15), just the number of switches on the keypad. Open and click [Run Continuously] in the LabVIEW program entitled Encoder.vi, as shown in Fig. 6.

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Fig. 6 Encoder Front Panel Displays Conversion of a Row and Column Address into 1 of 16 Numeric Key Codes

The row and column address lines are represented by two 4-bit arrays containing Boolean switches. Click on the allowable row and column addresses to see the resulting ‘Display Nybble’ and ‘Key Code’. Example:

Row (0100), column (0010) is the key numbered 7, but the binary code is 6.

Notes: The array index 0 is the least significant bit.

Within a LabVIEW program, binary counting starts at zero. The keypad is labeled from (1-9, A, B, C, D, *, #, or O), but the `’Key Code’ is (1-16).

Look at the block diagram of the Encoder.vi program, as shown in Fig. 7.

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Fig. 7 Encoder.vi Block Diagram

The program Encoder.vi takes the address nybbles from the scanning program and delivers a 4-bit binary array to the decoder program. Decoder The purpose of the decoder program is to convert a 4-bit input array into a selection of one and only one display. There are many ways to write this program. Here we have chosen to emulate a 74154 digital IC, which is a 1 of 16 data distributor. Open and [Run Continuously] the LabVIEW program entitled Decode.vi, as shown in Fig. 8.

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Fig. 8 Conversion of a 4-bit Binary Array Value into 1 of 16 LED-type Indicators Operate the binary switches to verify that each 4-bit binary combination yields a unique switch number (#). At the lower left, there is a box containing eight indicators. These represent the internal bus of the simulated 74154 chip, bits (0 - 3) and complements (0 - 3). Each indicator is decoded with a 4-bit AND function. This yields a true output only when its inputs are (1111). With our eight bus lines, one can uniquely select one and only one of the 16 combinations. Example:

Input bits (0101) [#11] goes to the bus as bits (0101) and complementary bits (0101).

Switch #11 is decoded with (b1 - b3) and (b0 - b2).

Stop the program and look at the block diagram. Observe how the input array is converted into the four input lines (b0 - b3) by the index array function. Four Boolean inverters are used to generate the complement bus lines (b0 - b3). All eight lines are terminated with a bus line indicators (B0-B3 and B0-B3). On the right side of the

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wiring diagram, there are sixteen four-input AND functions, each requiring a unique set of binary inputs to light its indicator (#). You can check out the emulation by searching the Web for 74154 IC. To observe the 16 color display, you load and [Run] the program Light Show.vi.

Exercise 6-3: Simon Says Program Version 1.0

Open and look at the block diagram of the LabVIEW program entitled Simon.vi, as shown in Fig. 9.

Fig. 9 Block Diagram of Simon.vi

When a key is pressed, Scanning.vi passes the row and column address to Encoder.vi, which generates a unique 4-bit binary for Decoder.vi. From the decoder, one of 16 indicators is lit on the front panel. Take Simon for a run and create some light shows. LabVIEW Challenge: Build a complete Simon Says game. You now have all of the major subVIs and a great front panel display.

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Here is the recipe: Randomly pick a number from 0 to 15 and display it for three

seconds.

Repeat this operation, say, three more times.

Store each random number into an array.

Use Simon Says Version 1 as a basis to get four key presses and record them into another array.

Compare the random numbers array with the guessed numbers

array.

If the arrays agree, then try another round with five random numbers.

Have Fun!