Frequency measurement

[hemnath]

I have measured the frequency using PIC micro-controller, but the accuracy is not good at higher frequency.

I have an idea for the better accuracy. I'm going to measure the no. of pulses occurred in a specific time duration(say about 100msec). That will give the frequency with better accuracy.

But i don't know how to count the rising edges during the 100 msec time interval. Please help

Thanks in advance

 

[udhay_cit]

Use one AND gate & connect a 100mS pulse generated from a uC port pin. Connect the output to the microcontroller Timer 1 clock input & configure the timer1 as a counter... reset the timer before you apply the 100mS pulse...

 

[hemnath]

I'm measuring the frequency from the function generator.

 

[jayanth.devarayanadurga]

**broken link removed**

 

[M.Imran Ali]

use external interrupt
use timer1 and load it with a value and scale it to form a sub multiple of 1 second and timer 1 overflow interrupt
on each ext_int increase variable frequency
after one second read variable frequency and it should be actual if you are using exact calculations

 

[paulfjujo]

hello,

.....
it should be actual if you are using exact calculations

if you are using prescaler different of 1/1
don't forget to add remaining counts inside prescaler to the global counting.
and survey timer overflow counting wich can occurs for high frequency...
you must add nb of overflow x 65536 to the final counting.

 

[M.Imran Ali]

yes that is thanx

 

[paulfjujo]

try to measure your Quartz itself !

What error do you get and at what frequency...

for comparaison it's what i get with mine

wct7_LCD.asm
avec correction +20 nop dans la boucle "Gate" et +16 nop en final
Ref . Affichage Mesure Gamme Error
4.000.000 Hz 4000065 Hz FREQ (1) -0.0016%
25.000 Hz 25000 Hz FREQ (1) 0
234.375 Hz 234374 Hz FREQ (1) 0.0004%
60,0 Mhz 59.9993 MHz VHF (2) 0.0012%
20,0 Mhz 19.9998 MHz VHF (2) 0.0010%