Engineers Garage

Tachometer using microcontroller

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Here is a trial of building a tachometer using AT89S52 Microcontroller. This is a digital tachometer which works using infrared rays. The tachometer designed here can measure rotational speed up to 4200 rpm which is sufficient for small scale use. If the speed goes beyond 4200 rpm, it gives a message on the display screen as “OUT OF RANGE”.

 
COMPONENTS:
 
1.      AT89S52 Microcontroller
2.      11.0592 MHz Crystal
4.      5V Power Supply
5.      Speed Sensor Module
 
Speed sensor module:
 
The speed sensor module is a completely home-made module to detect speed of a rotational body. The picture of the module that I have made is shown below. The function of this module is that it converts the speed of a rotational body to pulses. These pulses are fed to a microcontroller. The microcontroller counts them and displays them with a unit of rpm.
 
The components required to make the module are:
1.      Wheel of an optical mouse
2.      Plywood
3.      Screw bearing
4.      Steel rod (1 mm diameter, 10 cm long)
6.      Infrared Receiver (TSOP1738)
7.      Capacitor (47uF)
8.      Resistor (100R)
 
Take out the wheel of a damaged optical mouse and make a hole at the center of the wheel. Put the steel rod at the hole and glue it tightly so that the rod and the wheel rotate simultaneously. Make the plywood frame as shown in figure and screw the screw bearings on both sides so that the rod with the wheel can be mounted. After mounting the rod (with the wheel) on the screw bearings, try rotating the wheel with your finger. While rotating, the rod should have a minimum friction with the screw bearings. This will help measuring the exact speed. Then make the connections of the Infrared Transmitter and the Infrared Receiver as shown in the circuit diagram. Place the Infrared Transmitter on one side of the wheel and the Infrared Receiver on another side both facing each other. Here is a top view of the arrangement.
 
Don’t forget to make a hole on the wheel as shown in the picture below. It is extremely important. The hole will allow passing the infrared rays from the infrared transmitter to the infrared receiver.
 
Now you have your speed sensor module ready. This module should have four wires coming out of it. They are:- +5V Power Supply, Power Ground, wire connecting the  –ve terminal of the Infrared Transmitter and the wire connecting the output terminal of the TSOP1738 Infrared Receiver.
Let us now discuss how to connect this above made module to the microcontroller.
CIRCUIT DIAGRAM:
The circuit diagram should be connected as shown in the Circuit Diagram tab. The 5V Power and Ground of the speed sensor module should be connected to the Power supply to the circuit. The –ve terminal of the infrared transmitter and the output terminal of the infrared receiver should be connected to the specified pins of the microcontroller (see circuit diagram).
 

 OPERATION & PROGRAM STRUCTURE

OPERATION:               
 
OPERATION.jpg
 
To measure speed of a rotational body, you need to hold the speed sensor module by its frame and make contact of the wheel with the rotating body. Soon the wheel will start rotating at the speed of the rotational body. Holding the module in that position, press the reset button of the microcontroller. The speed of the rotational body will be displayed on the LCD screen.
 
Now let us go inside the process and discover what happens during the whole process. When the wheel of the module has no contact with any rotating body, it remains in a still position. So the infrared rays coming out from the transmitter are restricted by the wheel from entering the Infrared receiver. So the output of the infrared receiver is also still and not pulsating. The output of the infrared receiver is connected to COUNTER1 of the microcontroller and it can count only pulsating signals (not a still signal). So no pulses are generated by the infrared receiver and consequently no counting occurs. The display shows 00 rpm in this position.
When the user makes contact of the wheel of the module with a rotational body, the wheel starts rotating at the speed of the rotational body and the hole in the wheel will allow infrared rays to pass from the transmitter to the receiver once in a rotation. This will form a pulsating output of the infrared receiver and the counter in the microcontroller now can count the pulse. As these pulses are proportional to the speed, the counted pulse will represent the speed of the rotational body. That is what happens during the process.   
 
PROGRAM STRUCTURE:
 
The program first sets the TIMER2 of the microcontroller to generate 38 KHz frequency. This frequency is then supplied to the Infrared Transmitter so that the Infrared Transmitter LED sends out infrared rays at the same frequency. It is because the TSOP1738 Infrared Receiver can receive infrared rays of 38 KHz only.
The program then starts the COUNTER1 of the microcontroller for one second so that the pulses coming from the Infrared Receiver can be counted. After one second, the counter is stopped again. It is because of the fact that a tachometer generally gives out reading with a unit of ROTATION PER MINUTE (RPM). So for the process someone needs to hold the speed sensor module in contact with a rotational body for a whole minute and then the counted value to be displayed with a unit of RPM. This process will be too tedious. But if the number of rotation in one second can be counted then multiplying the value with 60 will give rotation in one minute. So the counter is opened for one second by the program and the pulses are counted during the second. The counted value is then multiplied by 60 and then the final value is displayed on the LCD screen with a unit of RPM.
It is to mention here that though the words PULSE and ROTATION are used alternately during the description, they actually mean the same. Because for one rotation of the wheel, the hole in the wheel will allow the rays of the infrared transmitter to pass to the receiver once and consequently one pulse will be formed by the receiver. So the total numbers of pulses denote total number of rotation.
 

Video

 
Video

 

 

 

Project Source Code

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ORG 00H
HARDWARE_CONNECTION:
                        LCD_DATA  EQU P2
                        LCD_RS    EQU P3.6
                        LCD_EN    EQU P3.7                       
                       
SOFTWARE_VARIABLE:             
                        TEMPVAR_1 EQU R0
                        TEMPVAR_2 EQU R1
                        TEMPVAR_3 EQU R2
                        TEMPVAR_4 EQU R3
                        TEMPVAR_5 EQU R4
                        TEMPVAR_6 EQU R5
                        TEMPVAR_7 EQU R6
                        TEMPVAR_8 EQU R7
                       
LCD_INITIALIZATION:                
                        MOV A,#38H                                                                        
                        ACALL LCD_COMND_WRT
                        MOV A,#0CH
                        ACALL LCD_COMND_WRT
                        MOV A,#01H
                        ACALL LCD_COMND_WRT                    
                        MOV A,#80H                                                               
                        ACALL LCD_COMND_WRT
 
CLOCK:
                        MOV 0C9H,#02H  ;T2MOD
                        MOV 0CAH,#0B7H ;RCAP2L
                        MOV 0CBH,#0FFH ;RCAP2H
                        MOV 0CCH,#0B7H ;TL2        
                        MOV 0CDH,#0FFH ;TH2
                        MOV 0C8H,#04H  ;T2CON
 
ORIGIN:
                        MOV TH1,#00H
                        MOV TMOD,#60H
                        SETB TR1                 
                        ACALL DELAY_ONESEC
                        CLR TR1
                        MOV A,TL1
 
CMPR_0: CJNE A,#00H,CMPR_1
                        MOV A,#00H
                        ACALL BCD_TO_ASCII
                        LJMP RPM_DISPLAY
CMPR_1: CJNE A,#01H,CMPR_2
                        MOV A,#60H
                        ACALL BCD_TO_ASCII
                        LJMP RPM_DISPLAY
CMPR_2: CJNE A,#02H,CMPR_3
                        MOV A,#01H
                        ACALL BCD_TO_ASCII
                        MOV A,#20H
                        ACALL BCD_TO_ASCII
                        LJMP RPM_DISPLAY
CMPR_3: CJNE A,#03H,CMPR_4
                        MOV A,#01H
                        ACALL BCD_TO_ASCII
                        MOV A,#80H
                        ACALL BCD_TO_ASCII
                        LJMP RPM_DISPLAY
CMPR_4: CJNE A,#04H,CMPR_5
                        MOV A,#02H
                        ACALL BCD_TO_ASCII
                        MOV A,#40H
                        ACALL BCD_TO_ASCII
                        LJMP RPM_DISPLAY
CMPR_5: CJNE A,#05H,CMPR_6
                        MOV A,#03H
                        ACALL BCD_TO_ASCII
                        MOV A,#00H
                        ACALL BCD_TO_ASCII
                        LJMP RPM_DISPLAY
CMPR_6: CJNE A,#06H,CMPR_7
                        MOV A,#03H
                        ACALL BCD_TO_ASCII
                        MOV A,#60H
                        ACALL BCD_TO_ASCII
                        LJMP RPM_DISPLAY
CMPR_7: CJNE A,#07H,CMPR_8
                        MOV A,#04H
                        ACALL BCD_TO_ASCII
                        MOV A,#20H
                        ACALL BCD_TO_ASCII
                        LJMP RPM_DISPLAY
CMPR_8: CJNE A,#08H,CMPR_9
                        MOV A,#04H
                        ACALL BCD_TO_ASCII
                        MOV A,#80H
                        ACALL BCD_TO_ASCII
                        LJMP RPM_DISPLAY
CMPR_9: CJNE A,#09H,CMPR_10
                        MOV A,#05H
                        ACALL BCD_TO_ASCII
                        MOV A,#40H
                        ACALL BCD_TO_ASCII
                        LJMP RPM_DISPLAY
CMPR_10: CJNE A,#0AH,CMPR_11
                        MOV A,#06H
                        ACALL BCD_TO_ASCII
                        MOV A,#00H
                        ACALL BCD_TO_ASCII
                        LJMP RPM_DISPLAY
CMPR_11: CJNE A,#0BH,CMPR_12
                        MOV A,#06H
                        ACALL BCD_TO_ASCII
                        MOV A,#60H
                        ACALL BCD_TO_ASCII
                        LJMP RPM_DISPLAY
CMPR_12: CJNE A,#0CH,CMPR_13
                        MOV A,#07H
                        ACALL BCD_TO_ASCII
                        MOV A,#20H
                        ACALL BCD_TO_ASCII
                        LJMP RPM_DISPLAY
CMPR_13: CJNE A,#0DH,CMPR_14
                        MOV A,#07H
                        ACALL BCD_TO_ASCII
                        MOV A,#80H
                        ACALL BCD_TO_ASCII
                        LJMP RPM_DISPLAY
CMPR_14: CJNE A,#0EH,CMPR_15
                        MOV A,#08H
                        ACALL BCD_TO_ASCII
                        MOV A,#40H
                        ACALL BCD_TO_ASCII
                        LJMP RPM_DISPLAY
CMPR_15: CJNE A,#0FH,CMPR_16
                        MOV A,#09H
                        ACALL BCD_TO_ASCII
                        MOV A,#00H
                        ACALL BCD_TO_ASCII
                        LJMP RPM_DISPLAY
CMPR_16: CJNE A,#10H,CMPR_17
                        MOV A,#09H
                        ACALL BCD_TO_ASCII
                        MOV A,#60H
                        ACALL BCD_TO_ASCII
                        LJMP RPM_DISPLAY
CMPR_17: CJNE A,#11H,CMPR_18
                        MOV A,#10H
                        ACALL BCD_TO_ASCII
                        MOV A,#20H
                        ACALL BCD_TO_ASCII
                        LJMP RPM_DISPLAY
CMPR_18: CJNE A,#12H,CMPR_19
                        MOV A,#10H
                        ACALL BCD_TO_ASCII
                        MOV A,#80H
                        ACALL BCD_TO_ASCII
                        LJMP RPM_DISPLAY
CMPR_19: CJNE A,#13H,CMPR_20
                        MOV A,#11H
                        ACALL BCD_TO_ASCII
                        MOV A,#40H
                        ACALL BCD_TO_ASCII
                        LJMP RPM_DISPLAY
CMPR_20: CJNE A,#14H,CMPR_21
                        MOV A,#12H
                        ACALL BCD_TO_ASCII
                        MOV A,#00H
                        ACALL BCD_TO_ASCII
                        LJMP RPM_DISPLAY
CMPR_21: CJNE A,#15H,CMPR_22
                        MOV A,#12H
                        ACALL BCD_TO_ASCII
                        MOV A,#60H
                        ACALL BCD_TO_ASCII
                        LJMP RPM_DISPLAY
CMPR_22: CJNE A,#16H,CMPR_23
                        MOV A,#13H
                        ACALL BCD_TO_ASCII
                        MOV A,#20H
                        ACALL BCD_TO_ASCII
                        LJMP RPM_DISPLAY
CMPR_23: CJNE A,#17H,CMPR_24
                        MOV A,#13H
                        ACALL BCD_TO_ASCII
                        MOV A,#80H
                        ACALL BCD_TO_ASCII
                        LJMP RPM_DISPLAY
CMPR_24: CJNE A,#18H,CMPR_25
                        MOV A,#14H
                        ACALL BCD_TO_ASCII
                        MOV A,#40H
                        ACALL BCD_TO_ASCII
                        LJMP RPM_DISPLAY
CMPR_25: CJNE A,#19H,CMPR_26
                        MOV A,#15H
                        ACALL BCD_TO_ASCII
                        MOV A,#00H
                        ACALL BCD_TO_ASCII
                        LJMP RPM_DISPLAY
CMPR_26: CJNE A,#1AH,CMPR_27
                        MOV A,#15H
                        ACALL BCD_TO_ASCII
                        MOV A,#60H
                        ACALL BCD_TO_ASCII
                        LJMP RPM_DISPLAY
CMPR_27: CJNE A,#1BH,CMPR_28
                        MOV A,#16H
                        ACALL BCD_TO_ASCII
                        MOV A,#20H
                        ACALL BCD_TO_ASCII
                        LJMP RPM_DISPLAY
CMPR_28: CJNE A,#1CH,CMPR_29
                        MOV A,#16H
                        ACALL BCD_TO_ASCII
                        MOV A,#80H
                        ACALL BCD_TO_ASCII
                        LJMP RPM_DISPLAY
CMPR_29: CJNE A,#1DH,CMPR_30
                        MOV A,#17H
                        ACALL BCD_TO_ASCII
                        MOV A,#40H
                        ACALL BCD_TO_ASCII
                        LJMP RPM_DISPLAY
CMPR_30: CJNE A,#1EH,CMPR_31
                        MOV A,#18H
                        ACALL BCD_TO_ASCII
                        MOV A,#00H
                        ACALL BCD_TO_ASCII
                        LJMP RPM_DISPLAY
CMPR_31: CJNE A,#1FH,CMPR_32
                        MOV A,#18H
                        ACALL BCD_TO_ASCII
                        MOV A,#60H
                        ACALL BCD_TO_ASCII
                        LJMP RPM_DISPLAY
CMPR_32: CJNE A,#20H,CMPR_33
                        MOV A,#19H
                        ACALL BCD_TO_ASCII
                        MOV A,#20H
                        ACALL BCD_TO_ASCII
                        LJMP RPM_DISPLAY
CMPR_33: CJNE A,#21H,CMPR_34
                        MOV A,#19H
                        ACALL BCD_TO_ASCII
                        MOV A,#80H
                        ACALL BCD_TO_ASCII
                        LJMP RPM_DISPLAY
CMPR_34: CJNE A,#22H,CMPR_35
                        MOV A,#20H
                        ACALL BCD_TO_ASCII
                        MOV A,#40H
                        ACALL BCD_TO_ASCII
                        LJMP RPM_DISPLAY
CMPR_35: CJNE A,#23H,CMPR_36
                        MOV A,#21H
                        ACALL BCD_TO_ASCII
                        MOV A,#00H
                        ACALL BCD_TO_ASCII
                        LJMP RPM_DISPLAY
CMPR_36: CJNE A,#24H,CMPR_37
                        MOV A,#21H
                        ACALL BCD_TO_ASCII
                        MOV A,#60H
                        ACALL BCD_TO_ASCII
                        LJMP RPM_DISPLAY
CMPR_37: CJNE A,#25H,CMPR_38
                        MOV A,#22H
                        ACALL BCD_TO_ASCII
                        MOV A,#20H
                        ACALL BCD_TO_ASCII
                        LJMP RPM_DISPLAY
CMPR_38: CJNE A,#26H,CMPR_39
                        MOV A,#22H
                        ACALL BCD_TO_ASCII
                        MOV A,#80H
                        ACALL BCD_TO_ASCII
                        LJMP RPM_DISPLAY
CMPR_39: CJNE A,#27H,CMPR_40
                        MOV A,#23H
                        ACALL BCD_TO_ASCII
                        MOV A,#40H
                        ACALL BCD_TO_ASCII
                        LJMP RPM_DISPLAY
CMPR_40: CJNE A,#28H,CMPR_41
                        MOV A,#24H
                        ACALL BCD_TO_ASCII
                        MOV A,#00H
                        ACALL BCD_TO_ASCII
                        LJMP RPM_DISPLAY
CMPR_41: CJNE A,#29H,CMPR_42
                        MOV A,#24H
                        ACALL BCD_TO_ASCII
                        MOV A,#60H
                        ACALL BCD_TO_ASCII
                        LJMP RPM_DISPLAY
CMPR_42: CJNE A,#2AH,CMPR_43
                        MOV A,#25H
                        ACALL BCD_TO_ASCII
                        MOV A,#20H
                        ACALL BCD_TO_ASCII
                        LJMP RPM_DISPLAY
CMPR_43: CJNE A,#2BH,CMPR_44
                        MOV A,#25H
                        ACALL BCD_TO_ASCII
                        MOV A,#80H
                        ACALL BCD_TO_ASCII
                        LJMP RPM_DISPLAY
CMPR_44: CJNE A,#2CH,CMPR_45
                        MOV A,#26H
                        ACALL BCD_TO_ASCII
                        MOV A,#40H
                        ACALL BCD_TO_ASCII
                        LJMP RPM_DISPLAY
CMPR_45: CJNE A,#2DH,CMPR_46
                        MOV A,#27H
                        ACALL BCD_TO_ASCII
                        MOV A,#20H
                        ACALL BCD_TO_ASCII
                        LJMP RPM_DISPLAY
CMPR_46: CJNE A,#2EH,CMPR_47
                        MOV A,#27H
                        ACALL BCD_TO_ASCII
                        MOV A,#80H
                        ACALL BCD_TO_ASCII
                        LJMP RPM_DISPLAY
CMPR_47: CJNE A,#2FH,CMPR_48
                        MOV A,#28H
                        ACALL BCD_TO_ASCII
                        MOV A,#40H
                        ACALL BCD_TO_ASCII
                        LJMP RPM_DISPLAY
CMPR_48: CJNE A,#30H,CMPR_49
                        MOV A,#29H
                        ACALL BCD_TO_ASCII
                        MOV A,#00H
                        ACALL BCD_TO_ASCII
                        LJMP RPM_DISPLAY
CMPR_49: CJNE A,#31H,CMPR_50
                        MOV A,#29H
                        ACALL BCD_TO_ASCII
                        MOV A,#60H
                        ACALL BCD_TO_ASCII
                        LJMP RPM_DISPLAY
CMPR_50: CJNE A,#32H,CMPR_51
                        MOV A,#30H
                        ACALL BCD_TO_ASCII
                        MOV A,#20H
                        ACALL BCD_TO_ASCII
                        LJMP RPM_DISPLAY
CMPR_51: CJNE A,#33H,CMPR_52
                        MOV A,#30H
                        ACALL BCD_TO_ASCII
                        MOV A,#80H
                        ACALL BCD_TO_ASCII
                        LJMP RPM_DISPLAY
CMPR_52: CJNE A,#34H,CMPR_53
                        MOV A,#31H
                        ACALL BCD_TO_ASCII
                        MOV A,#40H
                        ACALL BCD_TO_ASCII
                        LJMP RPM_DISPLAY
CMPR_53: CJNE A,#35H,CMPR_54
                        MOV A,#32H
                        ACALL BCD_TO_ASCII
                        MOV A,#00H
                        ACALL BCD_TO_ASCII
                        LJMP RPM_DISPLAY
CMPR_54: CJNE A,#36H,CMPR_55
                        MOV A,#32H
                        ACALL BCD_TO_ASCII
                        MOV A,#60H
                        ACALL BCD_TO_ASCII
                        LJMP RPM_DISPLAY
CMPR_55: CJNE A,#37H,CMPR_56
                        MOV A,#33H
                        ACALL BCD_TO_ASCII
                        MOV A,#20H
                        ACALL BCD_TO_ASCII
                        LJMP RPM_DISPLAY
CMPR_56: CJNE A,#38H,CMPR_57
                        MOV A,#33H
                        ACALL BCD_TO_ASCII
                        MOV A,#80H
                        ACALL BCD_TO_ASCII
                        LJMP RPM_DISPLAY
CMPR_57: CJNE A,#39H,CMPR_58
                        MOV A,#34H
                        ACALL BCD_TO_ASCII
                        MOV A,#40H
                        ACALL BCD_TO_ASCII
                        LJMP RPM_DISPLAY
CMPR_58: CJNE A,#3AH,CMPR_59
                        MOV A,#35H
                        ACALL BCD_TO_ASCII
                        MOV A,#00H
                        ACALL BCD_TO_ASCII
                        LJMP RPM_DISPLAY
CMPR_59: CJNE A,#3BH,CMPR_60
                        MOV A,#35H
                        ACALL BCD_TO_ASCII
                        MOV A,#60H
                        ACALL BCD_TO_ASCII
                        LJMP RPM_DISPLAY
CMPR_60: CJNE A,#3CH,CMPR_61
                        MOV A,#36H
                        ACALL BCD_TO_ASCII
                        MOV A,#20H
                        ACALL BCD_TO_ASCII
                        LJMP RPM_DISPLAY
CMPR_61: CJNE A,#3DH,CMPR_62
                        MOV A,#36H
                        ACALL BCD_TO_ASCII
                        MOV A,#80H
                        ACALL BCD_TO_ASCII
                        LJMP RPM_DISPLAY        
CMPR_62: CJNE A,#3EH,CMPR_63
                        MOV A,#37H
                        ACALL BCD_TO_ASCII
                        MOV A,#40H
                        ACALL BCD_TO_ASCII
                        LJMP RPM_DISPLAY
CMPR_63: CJNE A,#3FH,CMPR_64
                        MOV A,#38H
                        ACALL BCD_TO_ASCII
                        MOV A,#00H
                        ACALL BCD_TO_ASCII
                        LJMP RPM_DISPLAY
CMPR_64: CJNE A,#40H,CMPR_65
                        MOV A,#38H
                        ACALL BCD_TO_ASCII
                        MOV A,#60H
                        ACALL BCD_TO_ASCII
                        LJMP RPM_DISPLAY
CMPR_65: CJNE A,#41H,CMPR_66
                        MOV A,#39H
                        ACALL BCD_TO_ASCII
                        MOV A,#20H
                        ACALL BCD_TO_ASCII
                        LJMP RPM_DISPLAY
CMPR_66: CJNE A,#42H,CMPR_67
                        MOV A,#39H
                        ACALL BCD_TO_ASCII
                        MOV A,#80H
                        ACALL BCD_TO_ASCII
                        LJMP RPM_DISPLAY
CMPR_67: CJNE A,#43H,CMPR_68
                        MOV A,#40H
                        ACALL BCD_TO_ASCII
                        MOV A,#40H
                        ACALL BCD_TO_ASCII
                        LJMP RPM_DISPLAY
CMPR_68: CJNE A,#44H,CMPR_69
                        MOV A,#41H
                        ACALL BCD_TO_ASCII
                        MOV A,#00H
                        ACALL BCD_TO_ASCII
                        LJMP RPM_DISPLAY
CMPR_69: CJNE A,#45H,CMPR_70
                        MOV A,#41H
                        ACALL BCD_TO_ASCII
                        MOV A,#60H
                        ACALL BCD_TO_ASCII
                        LJMP RPM_DISPLAY
CMPR_70: CJNE A,#46H,EXIT
                        MOV A,#42H
                        ACALL BCD_TO_ASCII
                        MOV A,#20H
                        ACALL BCD_TO_ASCII
                        LJMP RPM_DISPLAY
 
EXIT:  MOV DPTR,#NO_RANGE                
                        ACALL STRING_DISPLAY
                        SJMP $
 
RPM_DISPLAY:
                        MOV A,#' '
                        ACALL LCD_DATA_WRT
                        MOV DPTR,#RPM                  
                        ACALL STRING_DISPLAY
                        SJMP $
 
LCD_COMND_WRT:                                                                                                 
                        MOV LCD_DATA,A
                        CLR LCD_RS
                        SETB LCD_EN
                        ACALL DELAY_NINE
                        CLR LCD_EN
                        RET
 
LCD_DATA_WRT:                                                                                      
                        MOV LCD_DATA,A
                        SETB LCD_RS
                        SETB LCD_EN
                        ACALL DELAY_NINE
                        CLR LCD_EN
                        RET
 
BCD_TO_ASCII:
                        MOV TEMPVAR_4,A
                        ANL A,#0FH
                        ORL A,#30H
                        MOV TEMPVAR_3,A
                        MOV A,TEMPVAR_4
                        ANL A,#0F0H
                        SWAP A
                        ORL A,#30H
                        ACALL LCD_DATA_WRT
                        ACALL DELAY_NINE
                        MOV A,TEMPVAR_3
                        ACALL LCD_DATA_WRT
                        ACALL DELAY_NINE
                        RET
 
DELAY_NINE:        
        MOV TEMPVAR_5,#16                                                          
                        NINE_BACK:MOV TEMPVAR_6,#250    
                        DJNZ TEMPVAR_6,$                      
                        DJNZ TEMPVAR_5,NINE_BACK
                        RET
 
DELAY_ONESEC:
                        MOV TEMPVAR_5,#10         
BK_C: MOV TEMPVAR_6,#255       
BK_B: MOV TEMPVAR_7,#179       
BK_A:            DJNZ TEMPVAR_7,BK_A
                        DJNZ TEMPVAR_6,BK_B
                        DJNZ TEMPVAR_5,BK_C
                        MOV TEMPVAR_6,#50
BK_E: MOV TEMPVAR_5,#9
BK_D:            DJNZ TEMPVAR_5,BK_D
                        DJNZ TEMPVAR_6,BK_E
                        RET
 
STRING_DISPLAY:                                                                                                
        DIS_BACK:CLR A
                        MOVC A,@A+DPTR
                        JZ DIS_OUT
                        ACALL LCD_DATA_WRT
                        INC DPTR
                        SJMP DIS_BACK
                DIS_OUT:RET
 
RPM: DB 'RPM',0
NO_RANGE: DB 'OUT OF RANGE',0
 
                        END
 
###
 

Circuit Diagrams



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