3x3 Matrix Keyboard using AT89C2051 microcontroller


Project Name: 3x3 Matrix Keyboard

Objective of Project:

Showing 0 to 8 on a 7 segment display by using matrix theory connected to P3.0 to P3.5

Circuit Diagram:




List of components:

SL
Name and Description
Quantity
1
MCU 89C2051
1
2
7 segment display ( Common Anode )
1
3
Resistance 1K Ohm
10
4
Capacitors 30pf
(10 uf 50Volt(1), 100uf 50Volt(1))
2
5
Crystal Q11.059A1
1
6
Voltage regulator 7805
1
7
Bread board
1
8
Connecting wires

9
Battery 9 Volt
1
10
Micro Push Type Switch
9



Flow Chart:



Program:
ORG 00h
                MOV P1, #0FFh

                Starter:                
                MOV P3, #00111000b
                MOV A, P3
                ANL A, #00111000b
                CJNE A, #00111000b, Starter
               
                KeyCheck:          
                CALL Delay
                MOV A, P3
                ANL A, #00111000b
                CJNE A, #00111000b, Debonc
                SJMP KeyCheck
               
                Debonc:              
                CALL Delay
                MOV A, P3
                ANL A, #00111000b
                CJNE A, #00111000b, FindRow
                SJMP KeyCheck
               
                FindRow:            
                MOV P3, #11111110b
                MOV A, P3
                ANL A, #00111000b
                CJNE A, #00111000b, Row_0
                MOV P3, #11111101b
                MOV A, P3
                ANL A, #00111000b
                CJNE A, #00111000b, Row_1
                MOV P3, #11111011b
                MOV A, P3
                ANL A, #00111000b
                CJNE A, #00111000b, Row_2
                LJMP KeyCheck
               
                Row_0:
                MOV DPTR, #Row_0_Data
                SJMP Find_Col
               
                Row_1:
                MOV DPTR, #Row_1_Data
                SJMP Find_Col
               
                Row_2:
                MOV DPTR, #Row_2_Data
                SJMP Find_Col
               
                Find_Col:            
                MOV R2, #03
                CLR C
               
                Get_col:              
                RRC A
                DJNZ R2, Get_col
               
                Find_Main:        
                RRC A
                JNC Matched
                INC DPTR
                SJMP Find_Main
               
                Matched:           
                CLR A
                MOVC A, @A+DPTR
                MOV P1, A
                LJMP Starter
               
                Delay:   MOV R5, #50h
                Del_1:   MOV R6, #10h
                Del_2:   DJNZ R6, Del_2
                DJNZ R5, Del_1
                RET
               
                Row_0_Data: db 0C0h, 0F9h, 0A4h
                Row_1_Data: db 0B0h, 99h, 92h
                Row_2_Data: db 82h, 0F8h, 80h
END

Brief Description of Program:

Rows are connected to Port P3.0, P3.1, and P3.2 respectively. And Columns are connected to P3.3, P3.4, and P3.5 respectively.
In the ‘start’ we put some value in accumulator register through port p3. Then we make an AND operation and run a loop ranges from 00111000b to the new value of accumulator register. After that, inside ‘check’, we call a delay and here we start to get the value of row0, row1 and row2 respectively. In the look up table data are kept within three rows.

Matrix Keyboard Connection to ports
  • •         Rows are connected to Port P3.0, P3.1, and P3.2 respectively.
  • •         Columns are connected to P3.3, P3.4, and P3.5 respectively.
  • •         If all the rows are grounded and a key is pressed, one of the columns will have 0 since the key pressed provides the path to ground.
  • •         If no key has been pressed, reading the input port will yield 1s for all columns since they are all connected to high (Vcc).


Detect a key press
  • •         To detect a pressed key, the microcontroller grounds all rows by providing 0 to the output           latch,
  • •         Then it reads the columns
Ø  If the data read from columns is D2 – D0 =111, no key has been pressed and the process continues till key press is detected
Ø  If one of the column bits has a zero, this means that a key press has occurred
For example, if D2 – D0 = 101, this means that a key in the D1 column has been pressed.

Detect row of key press
  • •         To detect which row key press belongs to, it grounds one row at a time, reading the columns each time.

Ø  If it finds that all columns are high, this means that the key press cannot belong to that row
Ø  Therefore, it grounds the next row and continues until it finds the row the key press belongs to
  • •         Upon finding the row that the key press belongs to, it sets up the starting address for the look-up table holding the scan codes (or ASCII) for that row




Identify the key press
  • •         To identify the key press, it rotates the column bits, one bit at a time, into the carry flag and checks to see if it is low

•         Upon finding the zero, it pulls out the ASCII code for that key from the look-up table         otherwise, it increments the pointer to point to the next element of the look-up table .

Achievements (Result):
It is showing 0 t 8 on a 7 segment display by using matrix theory connected to P3.0 to P3.5.



See the project at https://youtu.be/xmYHmVd1MFY

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