problem in frequency counter using pic 16f877a

[sayf alawneh]

guys i really need help my project is to make a frequency counter (frequency meter) can cout frequency up to 5Mhz using TMR1 or TMR0 i am lookig since 2 weeks in every where but still cant understand cause every body explain it different way than the other ,,,, i just need to know the maximum frequency i can count using both timers and whatt is the relation between the max frequency i can count and the crystal oscillator ?
also lot of guys told me to use TMR1 but why TMR1 and not TMR0 ??? i know TMR1 is 16 bit and TMR0 is 8 bits
for my project i used TMR1 and i really dont know why
as a test i used PWM from pic16f877a and sent the pWM pulse to T1CkI in another 16f877a
but the accuracy wasnt good !! for example a pwm of 15 k HZ was read 15252 HZ an error of 252 HZ ???
also i couldnt read more than 30Khz i couldnt get the needed range from 1 hz to 5Mhz !! also i need good accuracy is the problem in the code??? here is the counter code guys

---

Code dot - [expand]
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
sbit LCD_RS at RB4_bit;
sbit LCD_EN at RB5_bit;
sbit LCD_D7 at RB0_bit;
sbit LCD_D6 at RB1_bit;
sbit LCD_D5 at RB2_bit;
sbit LCD_D4 at RB3_bit;sbit LCD_RS_Direction at TRISB4_bit;
sbit LCD_EN_Direction at TRISB5_bit;
sbit LCD_D7_Direction at TRISB0_bit;
sbit LCD_D6_Direction at TRISB1_bit;
sbit LCD_D5_Direction at TRISB2_bit;
sbit LCD_D4_Direction at TRISB3_bit;
void main() {
int c=0,i=0,n=0;
char txt[5],txt1[5],*res;;
lcd_init();
lcd_cmd(_LCD_CLEAR);
lcd_cmd(_LCD_CURSOR_OFF);
TRISC=1;
TRISB=0;
TRISD=0;
PORTD= 0;
TMR1L=0;
TMR1H=0;
LCD_OUT(1,1,"WORKING..");
delay_ms(500);
lcd_out(1,1," WORKING.");
delay_ms(500);
lcd_out(1,1," WORKING ");
T1CON= 0B00000011;delay_ms(1000);
T1CON= 0B00000010;
c= TMR1L;
i= TMR1H * 256;
n= c+i;
IntToStr(n,txt);
lcd_cmd(_LCD_CLEAR);
delay_ms(100);
lcd_out(1,1," FREQUENCY IS");
delay_ms(100);lcd_out(2,0,txt);
lcd_out(2,7," Hz ");
}

---

and the PWm code is simple just to generate a pulse with 15Khz
guys am really a newbie please i need help i really need it please explain to me as a newbie
i only have 5 days to finish this project

 

[esp1]

hi,
Look at this image, it suggests a external asynchronous 1imer clock period of 60nanosec, ~16MHz.

Use timer0 in conjunction with a timer0 interrupt clocked software counter to give a precise 1 second period for reading the Timer1 count.
Also use timer1 interrupt to clock a software counter, this will give a 24 bit value [ 8bit in software, 16 in timer1]

At the end of the 1 second period stop timer1, read timer1 and the timer1 interrupt counter.

Reset the timer 0 and timer1 counts to zero at the beginning each 1 second timer period.

E

 

[paulfjujo]

hello,

You can count over 30MHz with timers ..

What is your FOSC Quartz = ?

What accuracy has your delay of 1seconde (delay_ms(1000); ?

you said PWM is 15Khz ? are you sure it is ?

To cover a large range of frequency , You must handle overlap of timer ( TMR0IF or TMR1IF) ,
count number of overlaping and add NbOverlap*65536 to the last reading.
If you use a prescaler , you also must add pulses to count residual pulse in prescaler...

 

[D.A.(Tony)Stewart]

Counter accuracy is limited by accuracy of time interval of reference clock scaled down from OSC, measured in PPM. 1 ppm external TCXO crystal clocks are cheap these days. Max frequency only limited by HW counters of chip.

 

[sayf alawneh]

frequency meter code problem

this code is for frequency meter project
crystal oscillator is 12 Mhz
the external pulse is a square one with 300 Khz frequency
the code is designed to measure 524 Khz with prescalar value 1:8
but it only measure up to 63Khz only do u know the reason guys ?
am really lost in timers since 2 weeks
her is the code

---

Code C - [expand]
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
// LCD module connections
sbit LCD_RS at RB4_bit;
sbit LCD_EN at RB5_bit;
sbit LCD_D4 at RB0_bit;
sbit LCD_D5 at RB1_bit;
sbit LCD_D6 at RB2_bit;
sbit LCD_D7 at RB3_bit;
sbit LCD_RS_Direction at TRISB4_bit;
sbit LCD_EN_Direction at TRISB5_bit;
sbit LCD_D4_Direction at TRISB0_bit;
sbit LCD_D5_Direction at TRISB1_bit;
sbit LCD_D6_Direction at TRISB2_bit;
sbit LCD_D7_Direction at TRISB3_bit;// End LCD module connections
char i;
unsigned short cnt;
unsigned int freq_result;
// Define Messages
 
char message1[ ] = "Freq Hz";
 
char *freq = "00000";
 
void Display_Freq(unsigned int freq2write) {
 
freq[0] = (freq2write/10000)%10 + 48; // extrct hundred thousnads digit
freq[1] = (freq2write/1000)%10 + 48; //extract thousands digit
freq[2] = (freq2write/100)%10 + 48; //extract hundreds digit
freq[3] = (freq2write/10)%10 + 48; // Extract tens digit
freq[4] = freq2write%10 + 48; // Extract ones digit
Lcd_Out(1, 6, freq); // Display Frequency on LCD
 
}
void main()
{
TRISB = 0;
PORTB = 0xFF;
TMR1H = 0x00; // Initialize Timer1 register
TMR1L = 0x00; // Initialize Timer1 register
T1CON = 0B00110011; // Timer1 on, external input RC0 and 1:8 scalling
TMR1IF_bit = 0; // clear TMR1IF
 
TRISC = 0xff; // all input
//////////////////////#LCD INITIALIZATION#////////////////////
Lcd_Init(); // Initialize LCD
Lcd_Cmd(_LCD_CLEAR); // Clear display
Lcd_Cmd(_LCD_CURSOR_OFF); // Cursor off
/////////////////////////////////////////////////////////////
Lcd_Out(1,1,message1); // Write message1 in 1st row
do {
 
TMR1H = 0; // reset high byte of timer 1 (takes effect when low byte written)
TMR1L = 0; // reset low byte of timer 1 (also loads in high byte now)
 
Delay_ms(1000); // Delay 0.1 Sec
 
freq_result = TMR1L; // get low byte of timer 1 count (and read high byte to buffer)
freq_result += TMR1H*256; // add in the high byte from buffer
freq_result*=8;
Display_Freq(freq_result); // show the result on LCD
 
} while(1); // Infinite loop

---

 

[paulfjujo]

Re: frequency meter code problem

hello,

524KHz=> 524000 pulses per seconde !
divide by 8 => 65500 pulses per seconde
so 65,5KHz

it seems not multiply by 8.. did you activate Math library ?
try to display Freq_result before multiply by 8.
and try also with

T1SYNC: Timer1 External Clock Input Synchronization Control bit
When TMR1CS = 1:
1 = Do not synchronize external clock input

 

[paulfjujo]

hello,

I tested your programme on my Microchip IRDAboard 16F877
with Q=20Mhz
if i enter a TTL signal on RC0 25Khz
i get Freq= 25000 .. OK

tested OK , with output on LCD and UART.

Does your programme work correctly at this frequency ?
Is your signal correct (TTL level compliant at over 300Khz!)?

18:41:48.984> Freq= 24992
18:41:49.984> Freq= 24992
18:41:50.984> Freq= 24992
18:41:52.046> Freq= 25000
18:41:53.046> Freq= 24992
18:41:54.046> Freq= 25000
18:41:55.046> Freq= 24992
18:41:56.109> Freq= 24992
18:41:57.109> Freq= 25000
18:41:58.109> Freq= 24992
18:41:59.171> Freq= 25000

my 25KHz is comming from a Quartz 400KHz oscillator + CD4040 divider..

when i measure with
400Khz on RC0 ..i get a value of 6776 .
400000-5*65536=6784
like we get 5 overcount of timer1 ?

200Khz ...............................03384
200000-3*65536=3392
like 3 overtimer1 occured..



i printout the result before freqresult * by 8 ..measure it is correct!
i get 50000 for 400KHz

Probleme is on the size of Freq_result.. int 16bit ..up to 65535
need to use a long value to get over..

so 400Khz gives 400000 Hz

unsigned long LFreq;
...
Lfreq=(unsigned long) Freq_Result*8;

 

[sayf alawneh]

hello,

I tested your programme on my Microchip IRDAboard 16F877
with Q=20Mhz
if i enter a TTL signal on RC0 25Khz
i get Freq= 25000 .. OK

tested OK , with output on LCD and UART.

Does your programme work correctly at this frequency ?
Is your signal correct (TTL level compliant at over 300Khz!)?


my 25KHz is comming from a Quartz 400KHz oscillator + CD4040 divider..

when i measure with
400Khz on RC0 ..i get a value of 6776 .
400000-5*65536=6784
like we get 5 overcount of timer1 ?

200Khz ...............................03384
200000-3*65536=3392
like 3 overtimer1 occured..



i printout the result before freqresult * by 8 ..measure it is correct!
i get 50000 for 400KHz

Probleme is on the size of Freq_result.. int 16bit ..up to 65535
need to use a long value to get over..

so 400Khz gives 400000 Hz

unsigned long LFreq;
...
Lfreq=(unsigned long) Freq_Result*8;

ill try it and notify u with the result

 

[sayf alawneh]

Re: frequency meter code problem

hello,

524KHz=> 524000 pulses per seconde !
divide by 8 => 65500 pulses per seconde
so 65,5KHz

it seems not multiply by 8.. did you activate Math library ?
try to display Freq_result before multiply by 8.
and try also with

T1SYNC: Timer1 External Clock Input Synchronization Control bit
When TMR1CS = 1:
1 = Do not synchronize external clock input

man you are the best every thing worked perfect