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NEW: IKA-TACH, the new version of this tachometer! More accuracy, more compact design, AVR based!

99 000 RPM Contact-Less Digital Tachometer
Featuring LCD display and automatic DATA hold function
By Ibrahim Kamal
Last update: 14/7/10

Overview
This article describes how to build a contact -less tachometer (device used to count the revolutions per minute of a rotating shaft) using a 8051 microcontroller and a proximity sensor.

As the name implies, what makes this device special, is that it can very accurately measure the rotational speed of a shaft without even touching it. This is very interesting when making direct contact with the rotating shaft is not an option or will reduce the velocity of the shaft, giving faulty readings.

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.

A 600 mA.h Ni-Cd battery provides months of regular use of this device before it needs to be recharged.


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
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.

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;
         }
   }
}


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]

Discussion (Last 15 posts preview...)
Preview of the last 15 messages discussing this page. Messages are sorted from the newest to the oldest.
Posted by:
akashrg
on: 26 Jul 2010
99 000 RPM Contact-Less Digital Tachometer
['Quote ]
its very complicted
Posted by:
sumantaoo
on: 08 Jul 2010
Re: 99 000 RPM Contact-Less Digital Tachometer
['Quote ]
thank you sir for your help


now if i keep a reflecting object the red LED is glowing and when i remove it its not thats working fine as per your earlier reply.

but when i connect the 14,13 pin of mc to 3 , 7 pin respectively of 1st and 2nd lm358 and hold SW1 the lcd displays ". o 0 and ends with x" .and no rpm is displayed in both the line ie avg and max

i have oriented my IR led towards the white disk which is connected to a 300 rpm motor but still nothing works plzz help now .

sugest some future steps.


regards
sumanta roy
Posted by:
uttam
on: 01 Jul 2010
Re: 99 000 RPM Contact-Less Digital Tachometer
['Quote ]

Quoting sumantaoo: thank you i have done the same as u said and the LCD is working perfectly .


but my transmitter and reciever are not working .i have rechecked the connection , also i have read the article on IR proximity detector in this site .but i am unable to figure out the possible way to see that tran. and reci. are working or not

help me how should i check the IR transmission and reception ckt .and plzz tell how did you do it. also should the red led on the receptor ckt should always glow ???


regards
sumanta


No red LED will not glow always, keep some reflecting object infront of transmitter and receiver circuit and adjust the preset/Pot (10 K POT of receiver circuit) with patience ... if there is no any hardware mistake then it will work ! one thing -- try to understand how lm358 woking here as voltage comparator , You will get confidence to make it work, I made this circuit and it worked without any hardware modification. !
Regards,
Uttam
Posted by:
User avatar
ikalogic

on: 01 Jul 2010
Re: 99 000 RPM Contact-Less Digital Tachometer
['Quote ]
If the RED led on the receiver Ir circuit is always glowing, then you're in saturation. try playing with the potentiometer to change the sensitivity.

the red led should only glow when IR is reflected to the sensor.
Posted by:
sumantaoo
on: 01 Jul 2010
Re: 99 000 RPM Contact-Less Digital Tachometer
['Quote ]
thank you i have done the same as u said and the LCD is working perfectly .


but my transmitter and reciever are not working .i have rechecked the connection , also i have read the article on IR proximity detector in this site .but i am unable to figure out the possible way to see that tran. and reci. are working or not

help me how should i check the IR transmission and reception ckt .and plzz tell how did you do it. also should the red led on the receptor ckt should always glow ???


regards
sumanta
Posted by:
uttam
on: 01 Jul 2010
99 000 RPM Contact-Less Digital Tachometer
['Quote ]
Please .. publish Ikatach. soon, why delay.. loosing patience!!
regards,
Uttam
Posted by:
uttam
on: 30 Jun 2010
Re: 99 000 RPM Contact-Less Digital Tachometer
['Quote ]

Quoting sumantaoo: can some one explain me how to make the LCD connections with the port 0 pins on the bread board ???


You have to solder single strand wire with LCD terminal (be careful with LCD pin numbers) and then other side of the wire to be connected in breadboard ... if I understand your question,
in fact it is very comfortable to work in breadboard
regards,
Uttam Dutta
Posted by:
sumantaoo
on: 30 Jun 2010
Re: 99 000 RPM Contact-Less Digital Tachometer
['Quote ]
can some one explain me how to make the LCD connections with the port 0 pins on the bread board ???
Posted by:
User avatar
ikalogic

on: 17 Jun 2010
Re: 99 000 RPM Contact-Less Digital Tachometer
['Quote ]
Hello,

That's good news.. don't worry it happens to everybody!

ad for the counting problems, specially at low RPM, i am aware of this problem,

that's why i working on a new version:
viewtopic.php?f=17&t=935

You can follow it's development there, i am going to upload some video clips very soon.
Posted by:
uttam
on: 16 Jun 2010
99 000 RPM Contact-Less Digital Tachometer
['Quote ]
Finally it works, I am sorry to say that it was my blunder mistake of identifying LCD pin numbers, somehow it was in my mind that LCD pin starts from left side (keeping pins bottom side)and every time I was doing same mistake keeping other things ok. After normalizing the LCD connection it starts working ( program works without any modification)
I am really sorry you spend enough time for me and It was my fault.
circuit works perfectly, I am sending you some pics. by email.

I take out the blades from table fan and put a fully black colored CD with 1 inch by 1 inch white reflector, when rotates giving RPM but when I lowering the speed( by electronic fan regulator) display shows more rpm ( and when stopped rotation showing 0 rpm - it is ok) means in higher rpm it is giving steady and reliable rpm, but in lower speed why rpm showing more and very fluctuating also. Thanks and regards,
Uttam Dutta
Posted by:
User avatar
ikalogic

on: 13 Jun 2010
Re: 99 000 RPM Contact-Less Digital Tachometer
['Quote ]
Hummm i have only build this circuit 1 time :D, and i don't even have the hardware anymore.. does any one here have an idea to help our friend? :)
Posted by:
uttam
on: 13 Jun 2010
99 000 RPM Contact-Less Digital Tachometer
['Quote ]
I have used a very stable DC power supply.(http://jnaudin.free.fr/html/s_30vdc.htm), input is 220 , output variable DC, 1.2 to 30 V, I set it in 5V for this project.
I dismantle the complete hardware and assembled it again but problem became the same ,
only bot. line of LCD flashing like before !(all 5 X 7 dot matrix unit of the line become prominent and flashing), if width of "ena" is increased then flashing frequency decreased only.
Checked the voltage in pin 2 of LCD it is 4.99 V.
Again I checked the each and every point of hard ware, they are as per your schematic and no shorting / connection problem found,( this time I removed sensor i.e. the pin connection of 13 and 14 of micro) probably there is no hardware problem, I do not understand the software completely but it should work as you made it work.
Then where .....the problem... (I also put little delay with ini sequence and increased the width of ene -- but not worked)
I know you are busy with other project, but do you kindly give little time with my problem and suggest some solution.
Regards,
Uttam Dutta
Posted by:
User avatar
ikalogic

on: 11 Jun 2010
Re: 99 000 RPM Contact-Less Digital Tachometer
['Quote ]

Quoting uttam: Thank you for giving confidence and valuable guidence..
I increased the pulse width of "ena" as you told

like this
ena(){
P2_7 = 1;
[u][b]delay (50000); // delay (5);-- original
P2_7 = 0;
}
There was significant change in blinking pattern of LCD bot line, (blinking frequency become slow enough) but there was no character or any thing else in LCD
two more thing I want to tell you
1) there was voaltage change in pin 39 to 32(7 to 14 of LCD) of micro from 4.99 to 1.96 V(by multimeter)but no reflection in LCD.
2)there is always a 4.9V available in sensor's "ctrl" terminal and it is working without pressing the button connected with pin 21 of micro and ground.

Please tell me what should I do next
Regards,
Uttam Dutta


hmm... if the micro is working, and the software is the same.. there must be an issue in the hardware somewhere.. i assume you already double checked all the connections, and made sure there are no short circuits anywhere..

by the way, what do you mean by blinking? you mean a cursor (like this "_" ?)

your reset pin of the micro controller has a pull up? (you never know, maybe the micro is always resarting...)

what kind of power supply you are using? what is the voltage on pin 2 of the LCD? (i know it should be 5V, but again, there may be a wiring error, this happened to me before..)
Posted by:
uttam
on: 10 Jun 2010
99 000 RPM Contact-Less Digital Tachometer
['Quote ]
Thank you for giving confidence and valuable guidence..
I increased the pulse width of "ena" as you told

like this
ena(){
P2_7 = 1;
[u][b]delay (50000); // delay (5);-- original
P2_7 = 0;
}
There was significant change in blinking pattern of LCD bot line, (blinking frequency become slow enough) but there was no character or any thing else in LCD
two more thing I want to tell you
1) there was voaltage change in pin 39 to 32(7 to 14 of LCD) of micro from 4.99 to 1.96 V(by multimeter)but no reflection in LCD.
2)there is always a 4.9V available in sensor's "ctrl" terminal and it is working without pressing the button connected with pin 21 of micro and ground.

Please tell me what should I do next
Regards,
Uttam Dutta
Posted by:
User avatar
ikalogic

on: 10 Jun 2010
Re: 99 000 RPM Contact-Less Digital Tachometer
['Quote ]

Quoting uttam: This is what I got from LCD provider
"Standard 16x2 Character LCD Module with green backlight. These modules are based on standard HD44780 controller. Easy to connect with MCUs. Supports 4 or 8 bit data transfer. Can display 2 lines of 16 characters. "
Yes - I am confirming that 1k ohm pull up resitaces are properly connected (only thing I did not use netwaork resitance but separate 10 nos. of 1 k Ohm resitances -one terminal shoted with + ve bar and other connected with Micro pin 39, 38, 37, 36, 35, 34, 33 and 32.

and rest two are connected with pin 27 and 28.
I changed the crystal also, no difference, then again I checked the micro pin of different port by LEDBLINK program, they are working
What should I do next, Please suggest .
Regards,
Uttam Dutta


we're gonna make it work... next think i would suggest one more try on the source code: Can you add delays in the ena() function, to increase the pusle width of the ENABLE input?
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