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5hz
to 500 Khz Frequency-Meter
Home-made, accurate, and simple
solution!
By Ibrahim
Kamal
Last update:
4/4/08
 Overview
Based on the famous AT89C52 microcontroller , this 500
Khz frequency-Meter will be enough to trace and debug most
of your circuits, to adjust 555 timers frequency and perform
all kind of frequency measurements in Digital circuits.
And once you have this tool between your hand, you will
get used to it to the point of no-return! and you will say
"remember the days we adjusted the
frequency by trial and error till we get it..!"
Note: This tutorial assumes you already have some
basic notions about microcontrollers and general electronics
skills.
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To understand the block diagram below, you should recall the simplest
definition of frequency: "the number of occurrences
within a given time period". What we are trying to
do is to count the number of electric pulses during a time of one
second. To do this we need a counter, to count the pulses, and a
timer so that every 1000 milliseconds, the processor stop counting,
calculate the frequency and display it, then start counting again
from zero.
This is the principle of operation of a frequency meter, however,
to build a reliable frequency meter, we will need to do some more
mathematical operations. For example: Some operations will accurately
predict the frequency before waiting for a whole second to elapse,
which will also increase the refresh rate. Another minor upgrade
is to to display the average of the last 5 reading rather than displaying
the frequency instantaneously (which can cause lot of display flickering
if the frequency being measured is not very stable).
This project will be discussed in two Parts, the Hardware
and the Software.
The
Hardware Parts
Lets start by this
easy part,to make the project look far-or-less like a profession
lab equipment, well I simply built it in an old Avo-Meter,
one of those you find in stores for less than $5! (god bless
china!), and then painted it all in black. (it was originally
yellow!)
And by the way, after I hacked that poor Avo-Meter, I also
used the same leads for our frequency meter.
As you can notice in the picture, there are 4 seven segments
display
Finally you can also notice the 2 connections
for the leads (Blue shaded area).
those connectors are standard for the test leads of most AVO
meters and testing devices. |
 |
 The
Display
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Before Getting into the electronics,
here is a final trick: To make the display look even
neater and Protect it from dust and scratches, simply
add a thin plastic film on top of it (it will be
firmly held in its place when the frequency meter is
re-assembled). |
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The
electronics
I am sure that you understand that to accomplish
this project, we will need to perform some mathematical operations,
as mentioned before, to increase the performance of the device.
Thus we will rely on an AT89C52 microcontroller to perform all
the required tasks in this project.
The
Display system:
While being very
simple (as you can see in this diagram), the display system
can seem complicated due to the high number of connections
(as you can see in the schematic below).
The main idea for this display system, is to connect all the
7-segment cells together in parallel, but only power one of
them in the same time.
for example, here is the sequence to show the number "1984": |
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1-Send
the number "1" though the data lines
2-Energize the first cell while all other cells are off
3-wait for a short time delay (in my code i paused for 0.6
Millisecond)
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7-Send
the number "8" though the data lines
8-Energize the third cell while all other cells are off
9-wait for a short time delay..
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4-Send
the number "9" though the data lines
5-Energize the second cell while all other cells are off
6-wait for a short time delay.. |
10-Send
the number "4" though the data lines
11-Energize the fourth cell while all other cells are off
12-wait for a short time delay..
13-Start over from the step No: 1. |
Believe it or not, the human
eye wont notice anything wrong, because, with the given delays the
display will refresh at the rate of 375 cycles per second
(375 Hz!) and the human eye can hardly notice some flickering in
a display refreshing at 24 Hz.
Now That you understand the display process, you
should be able to easily follow the schematic above.
Here is a brief description:
| Q1,Q2,Q3,Q4 |
2N2222 switching transistors
to drive the 7-segment displays. |
| DD1 to DD4 |
7-segmets display, common Anode
type.
Note that it is called 7 segments, but
actually each cell contain 8 leds (7 leds for the digit, and
1 led for the decimal point) |
| R21 to R24 |
1Kohm pull up resistors |
| R35 to R38 |
100Kohm pull down resistors |
| U1 |
The AT89C52 Micro-Controller
(actually you can only see the Port 0 and the 4 used pins
of PORT 1) |
Input
leads connections:
Nothing
really critical about this part, since we only intend to measure
TTL frequencies, the input is directly fed to the TO pin of
the AT89C52, which will be used as a counter (more details
about this in the software part).
P1 and P2 are simply the 2 connections for
the test leads. Note that in order to make any kind of measurements
on another circuit, the ground of the Measurement device and
of the circuit being tested must be connected together,
this is why there are at least 2 leads in any testing device
(one for the Ground and one for the measured signal). |
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Power
Supply, clock generator, and reset button:
| The Power supply here is not
critical either, because the device will be powered from a
9V alkaline battery, so we don't need any filter capacitors,
we just need to reduce 9V to 5V, and this is simply the job
of the IC 7805 (Usually we add decoupling and filter capacitors
when there is a lot of disturbance like in motor controllers,
or AC to DC power supplies) |
Power supply |
This part is standard in any circuit
containing an AT89C52.
-The switch SW1 will reset the micro-controller and
start the program from the beginning.
-C1 and C2 are 27pF, any nearby value between 20 and
40 pF will work just fine.
-X is a 24 Mhz crystal. it is imperative to use a
crystal of this frequency, which is the maximum frequency
the AT89C52 can respond to. using a |
Clock generation, and reset button
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12Mhz crystals will result in maximum measurable
frequency of 250 Khz instead of 500Khz.
Don't forget to connect the PIN 31 to the 5V, otherwise the
microcontroller wont work. |
NOTE:
While I tried to make things as clear as i could, this is
not a tutorial to explain to beginners what is a microcontroller
and how to use it... |
Now you have to bear in mind the simple block diagram
of a frequency meter shown at the top of the
page. You can download the whole code in one file here,
but even a professional programmer would easily get lost in someone's
else code, so my advice is to try to understand how it is working,
and then write your own version of the code.
The
Main loop
Now, here is a simplified flow chart of the main
loop. next to each box, you can see the corresponding source code,
this can help you to understand how each step is programmed.
 |
setup_interrupts(){
EA = 1;
ET0 = 1; //Enable the Timer/counter
0 interrupt
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
TL0 = 0; //empty the counting
registers
TH0 = 0; //empty the counting
registers
TH1 = 100; //start timer 1
from 0
ET1 = 1; //enable timer 1 interrupt
TR1 = 1; //Enable Timer/counter
1 to count
PT0 = 1; // Lower priority
for timer 0
PT1 = 0; // higher priority
for timer 1
} |
calc_del++;
if (calc_del > (2248/scale)){ //
update data
calc_del = 0;
f = (TL0 + (TH0* 256));
sample[4] = sample[3];
sample[3] = sample[2];
sample[2] = sample[1];
sample[1] = sample[0];
sample[0] = f;
TL0 = 0; // reset the two registers
of
TH0 = 0; //
the 16 bit counter |
f = floor(
(sample[0] + sample[1]
+ sample[2]+ sample[3]+ sample[4]) /5
)*scale; |
void int_to_digits(unsigned
long number){
float itd_a,itd_b;
itd_a = itd_a = number / 10.0;
dig[3] = floor((modf(itd_a,&itd_b)* 10)+0.5);
itd_a = itd_b / 10.0;
dig[2] = floor((modf(itd_a,&itd_b)* 10)+0.5);
itd_a = itd_b / 10.0;
dig[1] = floor((modf(itd_a,&itd_b)* 10)+0.5);
itd_a = itd_b / 10.0;
dig[0] = floor((modf(itd_a,&itd_b)* 10)+0.5);
} |
if (f < 1000){
pt[0] = 128;
pt[1] = 0;
pt[2] = 0;
pt[3] = 0;
}else if ((f > 999) & (f < 10000)){
f = f / 1;
pt[0] = 128;
pt[1] = 0;
pt[2] = 0;
pt[3] = 0;
}else if ((f > 9999) & (f < 100000)){
f = f / 10;
pt[0] = 0;
pt[1] = 128;
pt[2] = 0;
pt[3] = 0;
}else if ((f > 99999) & (f < 1000000)){
f = f / 100;
pt[0] = 0;
pt[1] = 0;
pt[2] = 128;
pt[3] = 0;
}else if ((f > 999999)){
f = f / 1000;
pt[0] = 0;
pt[1] = 0;
pt[2] = 0;
pt[3] = 128;
}
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The
Counter and the Timer.
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function count_pulses() , which is linked
to the "Interrupt 1", will be executed
each time the TIMER 0 overflows. Actually
this should never happen, because the counting registers are
emptied every 1/5 second (if scale = 5, by default), but in
case the timer overflows, we should increase the variable:
"scale", hence the counting variables will be emptied
every 1/6 second, and if the the TIMER 0 still overflows,
scale will be increased to 7, and so on, until the system
stabilizes at a point where the counting registers are being
emptied fast enough, then the calculated frequency is correct. |
count_pulses()
interrupt 1 //counter 0 interrupt
{
if (scale < 200)
scale++;
}
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The function calc_and_disp()
will be executed every 0.66 millisecond (this is defined
by the variable TH1 in the setup_interrrupts()
function) Each time this function is executed, one of
the 4 7-segments is energized, and a corresponding digit is
being sent, then, next time the function is called, the next
digit is energized to show the next corresponding number...
And the sequence goes on as explained before in the display
system
Note: dcnt is the variable used to select
on of the 4 display cells. |
calc_and_disp()
interrupt 3 {
P0 = (bcd[dig[3-dcnt]] - pt[3-dcnt]) ;
P1 = ord[3-dcnt];
dcnt++;
if(dcnt > 3){
dcnt = 0;
}
} |
Now you should be able to build your own Frequency meter. To help
you a litle more, I'm giving you a zip file containing the full
schematic, the PCB design and the source 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:
ikalogic
on:
03 Nov 2009 |
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Re: 500 Khz Frequency meter (using AT89S52) |
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Quoting chats: Can this meter be used to verify output of a frequency generator.?
what are TTL frequencies? |
TTL = Transistor to Transistor logic, it is the most basic 0V / 5V logic levels.
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Posted
by:
chats
on:
03 Nov 2009 |
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Posted
by:
chats
on:
03 Nov 2009 |
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Posted
by:
ikalogic
on:
07 Jan 2009 |
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Re: 500 Khz Frequency meter (using AT89S52) |
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| Quoting tomhat: PLS can you tell me haw many ?m is the R20 R25 R27 R28 R29 R30 R31 R32 ???THNKS...thomas |
Depend on the desired intensity of the display.
Anything from 220 ohms to 2.2 kohms will do just fine.
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Posted
by:
tomhat
on:
07 Jan 2009 |
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Posted
by:
maddy
on:
25 Dec 2008 |
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Re: 500 Khz Frequency meter (using AT89S52) |
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hi, ibrahim actually i have made this frequency meter and when i try to measure the frequencies lower than 1khz than it reads wrong values. also its last digit always flicker on each frequency. plz tell me the reason and solution too. And tell me if i connect this frequency meter with 8038 output to measure frequency than it will work precisely or not. thanx for last reply. reply soon.
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Posted
by:
maddy
on:
26 Nov 2008 |
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Posted
by:
ikalogic
on:
22 Sep 2008 |
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Re: 500 Khz Frequency meter (using AT89S52) |
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Quoting rifnasahd: can i use this projects materials to make a digital tachometer to measure the rpm, with pic 16F84. and also i should use the 7-segment displays.
plz giv some explanations.
regardz,
rifnas ahamed |
Yes you can us this material for your project, but i can't give you much explanation about using PICs...  that's not my cup of tea!
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Posted
by:
rifnasahd
on:
22 Sep 2008 |
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500 Khz Frequency meter (using AT89S52) |
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can i use this projects materials to make a digital tachometer to measure the rpm, with pic 16F84. and also i should use the 7-segment displays.
plz giv some explanations.
regardz,
rifnas ahamed
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Posted
by:
ikalogic
on:
10 May 2008 |
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Re: 500 Khz Frequency meter (using AT89S52) |
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Quoting ingbaja: Thanks again for your answer.
OK, I canīt make the measuremenet on the wheels or the drive sahft becausse it rotates at a diferent speed that the engiene, and also itīs variable. The kart doesnīt have a shifting transmision, but you can change (prior to racing) the ratio between engine and drive shaft to optimize performance at each track.
Also I donīt have to put a magnetic sensor, the magnet is already there, it is used for the spark timing and since itīs a 1 piston two stroke engine, every pulse the magnet sends to the spark generator represents 1 revolution so i figured I could use that same pulse (since it is low voltage) |
Well you convinced me! good luck then!
Let me know how if you need help
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Posted
by:
ingbaja
on:
10 May 2008 |
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500 Khz Frequency meter (using AT89S52) |
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Thanks again for your answer.
OK, I canīt make the measuremenet on the wheels or the drive sahft becausse it rotates at a diferent speed that the engiene, and also itīs variable. The kart doesnīt have a shifting transmision, but you can change (prior to racing) the ratio between engine and drive shaft to optimize performance at each track.
Also I donīt have to put a magnetic sensor, the magnet is already there, it is used for the spark timing and since itīs a 1 piston two stroke engine, every pulse the magnet sends to the spark generator represents 1 revolution so i figured I could use that same pulse (since it is low voltage)
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Posted
by:
ingbaja
on:
09 May 2008 |
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Re: 500 Khz Frequency meter (using AT89S52) |
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Thanks for your answer. Actually I read the other article, but i donīt need a contach less feature (I canīt open the engine, well, I can but the shaft is very thin, an also it is very crouded in that part of the kart to put an optical mark and receiver) so i would prefer a "permanent" tachometer if you know what I mean and i think that using the magneto signal (wich is very easy to get) could save me some trouble. I need the tachometer not just for static testing, i need it in order to "take care" of my engine, since the kart has no gears and no rpm regulator and itīs quite common to "blow up" engines in long straights, so i figured out i could mount it on the steering wheel. Ther are some gadgets in the market wich could take care of my problem, but down here (Iīm from Mexico) theīre pretty expensive.
Thanks again
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