NEW:
IKA-TACH, the new version of this
tachometer! More accuracy, more compact design, AVR based!
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99 000 RPM Contact-Less Digital Tachometer
Featuring LCD display
and automatic DATA hold function
By Ibrahim
Kamal
Last update:
14/7/10
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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:
uttam
on:
30 Jan 2012 |
Re: 99 000 RPM Contact-Less Digital Tachometer |
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Quoting arunsaifi: hello sir, i had run the code using kiel. but a problem occuring in hardware and it not getting inturrept from sensor, so counter on lcd showing oooo value. off time sensor output voltage is 3.5v and on time voltage is 4.8. i think both is logic one i had used another circuit for sensor. but problem is due to sensor on command. i m trying to swich the sensor using transistor. is it not working if we provide ground to emmiter directly.
arun yadav |
M/S Arun, Then try the hexcode provided by Ika in his site, the check the hardware in each point. hope you get the fault. I made it , it works! regards- Uttam
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Posted
by:
arunsaifi
on:
30 Jan 2012 |
99 000 RPM Contact-Less Digital Tachometer |
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hello sir, i had run the code using kiel. but a problem occuring in hardware and it not getting inturrept from sensor, so counter on lcd showing oooo value. off time sensor output voltage is 3.5v and on time voltage is 4.8. i think both is logic one i had used another circuit for sensor. but problem is due to sensor on command. i m trying to swich the sensor using transistor. is it not working if we provide ground to emmiter directly.
arun yadav
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Posted
by:
joefliz
on:
15 Dec 2011 |
99 000 RPM Contact-Less Digital Tachometer |
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for "The modified IR proximity sensor" image, u use IR LED for sender, and also another IR LED for receiver. correct me if im wrong. what type of emitting diode u use at receiver which is D3? just to make sure before buying the component, ty
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Posted
by:
salleh
on:
07 Dec 2011 |
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Posted
by:
uttam
on:
06 Dec 2011 |
Re: 99 000 RPM Contact-Less Digital Tachometer |
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| Quoting joefliz: can u give a complete code that also included the display on lcd code? |
Joefliz, every thing is readymade available in the relevent topic, please download relevent Zip file and compile, for compilation see the basic topic available in this site (Home page) or readymade .file , only this you need to download, please patiently go through the different pages of this site , you get evey thing you are asking for, now question of understanding the code, you need C programming knowledge. Regards, Uttam
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Posted
by:
salleh
on:
05 Dec 2011 |
99 000 RPM Contact-Less Digital Tachometer |
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hello sir,may i ask u about the coding that u post in this discussion,,why i cant run the coding,,i try it many time but iit alway give an error like this,,"C:\MCC18\lkr\project3.c:1:Error [1027] unable to locate 'REGX51.h' ",,,may i know the name of software that u use to run the program?or can u give to me the software,,,
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Posted
by:
salleh
on:
05 Dec 2011 |
Re: 99 000 RPM Contact-Less Digital Tachometer |
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hello sir,i'm student and have many question to ask u,,, firstly may i get overall coding of this project ? 2.where do u compile the coding that u write in this project?i had write the half coding that u gave and i try build the coding at mplab but there has some error,,,the error about REG,,,
i need this answer urgently because i had take ur project to be my final year project,,and i'm sory because i take ur project to be my project,,,this semester i have to submit the hardware of this project,,,i'm very appreciate if u can help me,,, tq
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Posted
by:
herodientu1
on:
03 Nov 2011 |
99 000 RPM Contact-Less Digital Tachometer |
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[size=150>I wonder because I did not complete in C problem should only do what has to. but when writing to 89c51 programming error, the program too much programming data from the memory of the IC. I'm very in parcel and would not have solutions to experienced guidance or replaced with an IC containing a complete program. thank[/size>
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Posted
by:
uttam
on:
16 Oct 2011 |
Re: 99 000 RPM Contact-Less Digital Tachometer |
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Quoting aurelio: sir, good morning. i work a project about wind speed monitoring and it seems so hard to build a hall switching device...can a proximity sensor is fit to change that? and i used pic16f84a micro controller. is it ok to load your source code in mplab 8.50 and to program in icd2?
i am very appreciated your answers and reply... more power. |
Hello Aurelio, Same source code will not work for PIC16f84a, you need to develop completely separate source code for PIC micro, otherwise better to use atmel micro as mentioned, but I will suggest you to build "IKA-TACH: Our new contact less tachometer project" as per sensor part , I want to know how you are going to make your project for measurement of wind speed, I had some experience to work with hall sensor, it works flawlessly, but I want to know your project details. regards, Uttam Dutta
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Posted
by:
aurelio
on:
15 Oct 2011 |
99 000 RPM Contact-Less Digital Tachometer |
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sir, good morning. i work a project about wind speed monitoring and it seems so hard to build a hall switching device...can a proximity sensor is fit to change that? and i used pic16f84a micro controller. is it ok to load your source code in mplab 8.50 and to program in icd2?
i am very appreciated your answers and reply... more power.
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