Saturday, 24 June 2017

Input frequency measurement using LPC2148

Today I am going to discuss 'how to measure input frequency using LPC2148'. This is helpful in case when u don't have an oscillator and still want to measure frequency.

The process is very straight forward, you have to measure the number of times input pin goes high and low in 1 second. This measure will give you the frequency.

1.) Set a pin as input and make sure you connect a pull-up register to it. Pull-up is necessary otherwise pin will not go to high state.
2.) Give  in the frequency input to the pin and display the frequency on the serial terminal via UART.

Some Insight into the Code:-

IODIR1 |= (1<<18);    // will select the Port1.18 as input

while (1)
    if (!(IOPIN1&(1<<18)))    // if the pin is low
         while (!(IOPIN1&(1<<18)))    // wait until the pin is low
    else if (IOPIN1&(1<<18))    // if the pin is high
         while (IOPIN1&(1<<18))    // wait until the pin is high

     counter++;    // increment the counter by 1
     freq = increment/2;
     counter = 0;

#include <lpc214x.h>
#include <stdint.h>
#include "pll.h"
#include "timer0.h"
#include "uart0.h"
#include <stdio.h>

static uint32_t increment = 0;
uint32_t  time, freq;
char converted[6];
int main ()
PINSEL1 = 0;
IODIR0|= (0<<18);    // set P0.18 as input
pll_init ();    // initialsise pll clocks
VPBDIV = 0x00;    // set pclk = 15 MHz
timer0_init (15000000);    // initialize timer with 1 sec base 
Uart0_init ();    // initialize uart
while (1)
T0TC=0;    // set 0 to TC counter
T0TCR=(1<<1);    //reset timer
        T0TCR=(1<<0);    // enable timer 
while (T0TC<1)     // while loop for a delay of 1 second
if (!(IOPIN0&(1<<18)))    // if the pin is low
while(!(IOPIN0&(1<<18)));    // wait until the pin is low
else if ((IOPIN0&(1<<18)))     // if the pin is high
while (IOPIN0&(1<<18));     // wait until the pin is high
increment++;    // increment the counter
freq = increment/2;
increment = 0;

sprintf (converted, "%u", freq);
Uart0_Tx_string (converted);     // send via UART
Uart0_Tx_string (" Hz   \n");
while (*converted)
int i =0;
converted[i++] = 0;

That's it. You can change the frequency input in the clock and see the output in the debugger.
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Download full code with simulation HERE

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