| 99
000 RPM Contact-Less Digital Tachometer
Featuring LCD display
and automatic DATA hold function
By
Ibrahim Kamal
Last update:
4/4/08
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Key Features:
Measures up to 99 000 RPM
Instantaneous measurement
Automatic DATA Hold Function
LCD display
Ni-Cad Rechargeable battery |
Important:
this tachometer uses a proximity sensor. In case you don't
know how to make a proximity sensors, and/or how to operate
them, please refer to this
article first. |
Contact
less tachometer principle of operation
The idea behind
most digital counting device, frequency meters and tachometers,
is a micro-controller, used to count the pulses coming from
a sensor or any other electronic device.
In the case of this tachometer, the counted pluses will
come from proximity sensor, which will detect any reflective
element passing infront of it, and thus, will give an output
pulse for each and every rotation of the shaft, as show
in the picture. Those pulses will be fed to the microcontroller
and counted.
To understand how a micro |
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controller counts pulses, and deduce the frequency
of those pulse, please refer to this
tutorial about building a frequency meter, that elaborates
the process of frequency counting.
The main difference between this tutorial about
tachometer and frequency meters, is that we need the reading in
pulses per minutes (to count revolutions per minutes), but in
the same time, we don't want to wait a whole minute before getting
a correct reading. Thus we need some additional processing to
predict the number of revolutions per minute in less than a second.
Instantaneous
measurement algorithm
To
be able to deduce an RPM reading in less than second, while constantly
refining the reading's accuracy, a simple algorithm have been
developed, where a counter and a timer are used. Counter and timers
are part of the internal features of a micro-controller, (like
the AT89C52 used in this project) and they can be easily configured
through programming.
The schematic below, shows how the timer and the
counter are used for this task; The counter is connected i such
a way to count pulses coming from the proximity sensor, while
the timer is used to precisely feed the counted value to the microcontroller every filth of a second, and
reset
the counter to 0. The microcontroller can now take an
average of the last 3 readings (saved in C1, C2 and C3)
and calculate the average numbers of pulses per fifth
second, then multiply this value by 5, to get the number
of pulses per second, then multiply this value by 60 to
get the number of pulses per minute, which represents
the measured RPM. The only purpose of calculating an average
reading is that it will allow to get more |

C1, C2 and C3 are used to store the last 3 reading |
stable reading and prevent display flickering.
The
electronic Circuits
This device is composed of 2 electronic circuits: the
Sensor, which is a slightly modified proximity
sensor, and the microcontroller board, which analyses pulses
coming from the sensor, process them and display the result on
the LCD display.
The microcontroller board:
Circuit explanation:
The LCD connections
in the green shading is a standard for most of
alpha numeric LCDs, the only feature I added is to be able to
control the back light via the 80c52 microcontroller. The LCD
protocol can seem complicated to some of you, and an article should
be released soon to explain it.
The part in the blue shading
is also standard in any 8051 microcontroller circuit, which includes
the reset circuitry along with the crystal resonator that generates
the clock pulses required.
The power supply, shaded in light
red, regulates a 9V rechargeable Ni-CD battery
and also provides a very simple battery monitor, with a green
and a red LED, showing whether the battery need to be recharged
or not.
The switch SW1, shown in the upper yellow circle, is used to enable/disable
the measurement or the counting process. When the switch is pressed,
the device measures the RPM of the shaft under test, and constantly
updates the reading on the LCD, when the switch is released, the
last reading is held unchanged on the display, as long as the
device stays on. When the switch is pressed again the old reading
is replaced by the new one.
The wire connection P1, which is connected to
the output of the sensor, is connected to the pin 3.4 of the microcontroller, this pin has a dual function which is to count incoming
pulses and increment a 8, 13, or 16 bit register according to
the configuration of the timer T0.
As you may have noticed, this schematics misses tow important
items to be called a tachometer: The C code loaded into the microcontroller, which will be discussed later, and the proximity sensor,
which will feed the pulses to be counted.
The modified IR proximity sensor:
This schematic show the slight modification over
the one proposed in this tutorial,
which is the fact that the emitter LED uses a current limiting
resistor of a higher value, to allow it to be turned on for a
long period of time, because in this specific application, we
need to turn the IR emissions on or off, but we don't need to
inject high currents to reach high ranges... I recommend the reading
of this article that fully covers
all the aspects of this sensor.
The CTRL line, is an input coming from the microcontroller (at
the wire connection: P4), turning the IR emissions ON and
OFF, and the OUT line, is the output of the sensor, which is fed
to the microcontroller (at the wire connection: P1).
After analyzing both the main board holding the microcontroller
and the sensor, here is a simple
diagram
showing how they are connected together. You will have
to refer to the above schematics to see where P1, P2,
P3 and P4 goes in the main board, as well as the other
lines concerning the sensor.
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This
picture also shows what is meant by the connection of
the sensor to the main board. The reason for separating
the sensor from the main board, is to allow better performance
sensors, or even other types of sensors to be connected
to the device. In general, modular designs cost more,
but is more useful in the prototyping phase... |
The
software
Here are only small relevant parts
of the full C program, that was loaded into the microcontroller
after being compiled to a HEX file. Those part of the code were
selected as the ones that emphasize the main purpose of a microcontroller in such an application. For examples, function dealing
with the LCD operation are not included in this description. Comments
in green explains the program. The full code is available in the
Project folder, downloadable at the bottom of this article
.
#include
<REGX51.h>
#include <math.h>
unsigned
int clk_tmp,clk_tmp2,clk_sec,clk_sec2;
unsigned intex_pulses,rps,rps_tmp,temp,rps_avg,rps_max;
unsigned int rps_his[5];
char a,b,c,d,e;
unsigned char count1,count2;
unsigned char scale = 4;
delay(y){ // A function to make software
delays
unsigned int i;
for(i=0;i<y;i++){;}
} setup_interrupts(){
// This function initialises the
TIMER and the COUNTER to
EA = 1; //
be used in in the trachometre
ET0 = 1; //set
the Timer/counter 0
TR0 = 1; //Enable
Timer/counter 0 to count
TMOD = 0X25; //counter 0 in
mode 1 (16 bit counter),
//timer
1 in mode 2 (auto reload from TH1)
TH1 = 0; //start
counter from 0
ET1 = 1; //enable
timer 1
TR1 = 1; //Enable
Timer/counter 1 to count
PT0 = 1; //Setup
the priorities of timer 1 and timer 0, a 0 gives a
PT1 = 0; //higher
priority.
}
void int_to_digits(unsigned int number){ //store
the 5 digits of an integer
float itd_a,itd_b; //number
in the variable a,b,c,d,e
itd_a = number / 10.0;
e = floor((modf(itd_a,&itd_b)* 10)+0.5);
itd_a = itd_b / 10.0;
d = floor((modf(itd_a,&itd_b)* 10)+0.5);
itd_a = itd_b / 10.0;
c = floor((modf(itd_a,&itd_b)* 10)+0.5);
itd_a = itd_b / 10.0;
b = floor((modf(itd_a,&itd_b)* 10)+0.5);
itd_a = itd_b / 10.0;
a = floor((modf(itd_a,&itd_b)* 10)+0.5);
}
clk() interrupt 3 //timer
1 interrupt
{
clk_tmp++; //Software
counter for the timing of the tachometer readings
clk_tmp2++; //Software
counter for the display refresh rate
if (clk_tmp2 > (1236)){ //
update display
clk_tmp2 = 0;
rps_avg = floor(((rps_his[0] + rps_his[1] + rps_his[2]
+ rps_his[3] + ___
___rps_his[4])/5)*60);
}
if
(clk_tmp > (6584/scale)){ //
update the measured RPM
clk_tmp = 0;
if (P2_0 == 0){
rps = TL0;
temp = TH0;
temp = temp * 256;
rps = (rps + temp)* scale;
rps_his[4] = rps_his[3];
rps_his[3] = rps_his[2];
rps_his[2] = rps_his[1];
rps_his[1] = rps_his[0];
rps_his[0] = rps;
}
TL0 = 0;
TH0 = 0;
}
}
count_pulses() interrupt 1 //counter
0 interrupt
{
if (scale < 10) //
If the pulses are so fast that the internal counter
scale++; //
overflows, increase the variable 'scale' so that
} //
so that readings are recorded at a higher rate
void main(){
scale = 10 ;
P3_3 = 0; // ini
proximity sensor, OFF
P3_4 = 1; // ini
sensor input
P1_1 = 0; //turn
LCD backlight ON
P2_0 = 1; //ini
count/hold button
ini_lcd(); //
ini the LCD
setup_interrupts();
while(1){
P3_3 = ~P2_0;
if
(P2_0 == 1){
scale=
4;
}
}
}
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To understand the functioning of this source code, you must have
some basic microcontroller and C language skills.
The variable scale is used to control
the rate at which the tachometer reads and resets the counter.
The
housing of the tachometer
For the housing, an old floppy disk drive case is used,
where the tachometer and the battery fits perfectly. Here,
those few pictures are worth a thousands words.
(click on a picture to enlarge)
Download
the zip file for the project.
containing the PCB, Schematic and Example
8051 C51 code.
[note: i use ExpressPCB(FREEWARE)
to design the schematics and the PCB]
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Preview of the last 15
messages discussing this page. Messages are sorted from the newest to
the oldest. |
Posted
by:
yesindia
on:
07 Mar 2010 |
99 000 RPM Contact-Less Digital Tachometer |
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what is the meaning of ani??? what is the meaning of this below part???? pls. reply me fast if (ani == 0){ ani = 1; lcd_send (32); lcd_send (32); lcd_send (32); }else if(ani == 1){ ani = 2; lcd_send (46); lcd_send (32); lcd_send (32); }else if(ani == 2){ ani = 3; lcd_send (46); lcd_send (111); lcd_send (32); }else if(ani == 3){ ani = 0; lcd_send (46); lcd_send (111); lcd_send (79); } }else{ lcd_send (32); lcd_send (32); lcd_send (88); }
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Posted
by:
easycorps
on:
28 Feb 2010 |
99 000 RPM Contact-Less Digital Tachometer |
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This device is built on an AT89S52 (or AT89C52) microcontroller, an alpha-numeric LCD module and and a proximity sensor to detect the rotation of the shaft whose speed is being measured. Sory, my mistake, I did not correct read a given text.
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Posted
by:
j2th
on:
30 Jan 2010 |
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Posted
by:
elroes
on:
25 Jan 2010 |
99 000 RPM Contact-Less Digital Tachometer |
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I am working on a tachometer that will measure the rpm of a wind turbine. This article has been very helpful but there is a variation that I would like to try and was wondering if you had any input to give.
Instead of using an LCD display, I wish to output the RPM reading of the controller to a PC where other measurements are being made (power output of the turbine, current, voltage, etc). I am very new to microcontrollers and from what I understand this can be done relatively easily using a Serial (RS232) output. I know I will have to handle the output on the PC using some sort of program (either Labview or some homemade Visual Basic), but wanted some insight on what changes to the C-code on the controller might be. Thanks for your time!
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Posted
by:
tarak
on:
20 Jan 2010 |
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Posted
by:
meraj
on:
17 Jan 2010 |
99 000 RPM Contact-Less Digital Tachometer |
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hey IKA... its urjent n important... pls go through this... m unable to get proper output on the LCD display (only the light is turned on with checkered boxes on it)..... i doubt if the LCD interfacing code is present in the HEX code provided. please help me out...
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Posted
by:
nitishsingla1234
on:
16 Jan 2010 |
Re: 99 000 RPM Contact-Less Digital Tachometer |
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Hi......... first of all i would like to thank you for showing the simple and cost effective way to design and customize circuits. 1) I have a bike on which i wanna fit a tacho, but the problem is of collecting the pulses, where IT sensor cannot be mounted with ease. i have heard about collecting the pulses from ignition coil using optocoupler like MST2E. Can you please post an article based on this kind of application? 2) On vehicles, it becomes quite difficult to read the LCD. Infact, it isn't even required in many cases. So can you give another version of tachometer which consists of LED's glowing corresponding to RPM instead of LCD.
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Posted
by:
meraj
on:
15 Jan 2010 |
99 000 RPM Contact-Less Digital Tachometer |
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hii Ibrahim!!!! i have assembled whole ckt but m unable to get proper output on the LCD display (only the light is turned on with checkered boxes on it)..... i doubt if the LCD interfacing code is present in the HEX code provided. please help me out...my final deadline for the project submission is due now... it's urjenttt!!!!
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Posted
by:
vudiepdh1
on:
12 Jan 2010 |
Re: 99 000 RPM Contact-Less Digital Tachometer |
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Oh no ! A stupid mistake ! I ve been solved this problem ! So sorry Ika ! this is first time i use Keil I must to recognize that my c language is bad and English too ! =_< I have a question need help !Your project are using crystal 24mhz but i am using crystal 12mhz for cycle = 1 microsecond ! What i need to modify ur code to suit with it ! Thanks !
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Posted
by:
ikalogic
on:
11 Jan 2010 |
Re: 99 000 RPM Contact-Less Digital Tachometer |
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| Quoting vudiepdh1: Hi ika ! i have a problem with your code ! i try to recompile your c code into hex file by using keil! but i received a hex file 0 kB so what wrong ! or Keil c error ? |
what is the output of the compiler?
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