frequency counter using at89s51

[joajas]

Hi, I need to determined a square digital waveform's frequency. Any suggestions on how to do that?? I am thinking of using one of the i/o pins as input from and external source and determining that the frequency of the waveform on that input is 424hz. Please advice...

 

[whorse]

You can put the signal to the counter input pin, use the internal timer(for example, 1s interval) as the other resource. The working sequence is as follows:
i. start timer, at the same time, start the counter.
ii. check the timer's interrupt flag.
iii. when the timer's interrypt flag has been set (1s passed), stop the counter, read the counter number, then you got the frequency.

 

[joajas]

So.. How do I read the values from TH and TL??? :?: Please advice. Thank you and best regards.

 

[whorse]

It's quite easy to read TH and TL no matter using C or ASM code. If you can't do this now, you can do nothing on MCU, so just study the basic concept at first, a book on MCU will be suitible for you.

 

[amazonite]

You can use 12M Crystal in external Oscillator.Then the internal clock time is 1us/1clock (1(12M/12)).Use the Time0 in Mode 1.Than Set TR0=GATE0=1 and connect probe to P3.2. When the P3.2 is high level,the Time0(Conuter0) will count until the P3.2 change to low level.I suppose the count value is 100. the count value mean the 1 period is 200us.So the frequency is 1/200us.But the method must be high level equal low level of the square signal.

 

[ME]

Here's is a Frequency Counter based on Atmel ATmega8 AVR, with complete schematics and C source code.

Frequency Meter: www.microsyl.com/fmeter/fmeter.html

Main page with several other MCU projects www.microsyl.com