Wireless Phone Tic-Tac-Toe

Josh Morelli

Project Description

The purpose is to illustrate the interfacing of hardware and wireless phones using standard Dual-Tone Multi-Frequency (DTMF) signals.Because of delays associated with wireless phone transmissions, a time-insensitive project was necessary.Hence, Tic-Tac-Toe.

System Block Diagram

Operational Description

Player A presses a button 1-9.Player B’s phone receives the tone and sends it to the DTMF decoder through the 2.5mm headset jack.Player A’s phone does the same thing simultaneouslyDecoder outputs a 4-bit representation of button pressed to the HC12

Operational Description (cont)

HC12 immediately sends the same signal to a DTMF generatorGenerator sends identical tone back to Player A for acknowledgement (ACK)Once ACK is verified, HC12 processes the signal and illuminates the appropriate LED on the display board

Operational Description (cont)

HC12 then processes a simple algorithm to determine if a winning sequence has been litIf a winner is found, the winning sequence of LED’s is flashedPlay continues until a winner is found, or reset button is pressed

Algorithm Description

First checks one diagonal and all horizontal possibilities, then rotates pattern 90 degrees to check other diagonal and vertical possibilities.

Algorithm Description (cont)

HC12 will logically re-order board positions for pattern recognition. New order will allow rotation simply by bit-shifting one 8-bit register.

Original Re-ordered Rotated

Display Board

The display board will be the primary output component of the user interface.A 3x3 array of bi-color (red/green), three-leaded LED’s will be used to represent the traditional X’s and O’s.

Display Board (cont)

The LED array will be controlled by two 16-bit serial shift registers (74LS673) to reduce the number of HC12 pins used.Two 10-bit high-output buffers (TI P/N SN74ABT827) will provide the driving current for the LED array.Each LED will have a voltage divider attached to each of its 2 anodes to control proper voltages and currents.

Display Board SchematicSerial In

Shift Clock

16-b

it S

hift

Reg

iste

r (7

4LS

673)

10-b

it H

igh-

Out

put B

uffe

r (7

4AB

T82

7)

ParallelOut

x2 x2

DTMF Decoder

18-pin DIP IC (TDK P/N: TSC 75T202)No input signal filtering required4-bit output, binary representation of 12 possible standard phone buttonsUses a common, inexpensive reference crystal (3.579545 MHz)

DTMF Generator

16-pin DIP IC (TI P/N: TCM5089)4-bit row, 4-bit column input, combined to select output frequenciesOutput frequency error is ≤0.73%Also uses the 3.579545 MHz crystal

Cost EstimationQuantity Part # Description Cost Ext. Cost

2 68HC12 HC12 Evaluation Board $120.00 $240.002 V2010 4"x4" PC Board $6.66 $13.32

18 67-1327 3mm Red/Green LED $0.63 $11.342 TCM5089 DTMF Generator $1.25 $2.502 TSC 75T202 DTMF Decoder $4.50 $9.002 crystal 3.579545 MHz crystal $0.60 $1.202 LM7805 5V Regulator IC $0.40 $0.802 CAP1041 10uF capacitors $0.10 $0.20

36 resistors 270-ohm resistors $0.10 $3.6018 resistors 180-ohm resistors $0.10 $1.8018 resistors 220-ohm resistors $0.10 $1.804 74F675 16-bit shift register $6.83 $27.322 CAB1089 2.5mm stereo audio cables $0.69 $1.382 battery 7.2V battery packs $24.99 $49.982 phone Wireless phone $100.00 $200.00

Total $564.24