How to Connect a reed sensor to a PIC24 or any PIC?

[Pat ondo]

I am working on a project where I have to use two reeds sensors in order to get the velocity of a object travelling horizontally. The reed sensors are switches that close or open when they are near of a magnet. I was planing to use the ADC on the PIC but I read somewhere that in my case I do not have to do it because I would not need any voltage values between 0V and 5V. I will only need the minimum voltage and the maximum voltage value. So, I want to know how I can actually connect those sensors to the micro controller. And what can I do to get the time between the two microcontroller when they close or open?

Thanks

[AJISH ALFRED]

Hi,

You can make any IO pin as input and conncet the Reed swicth just like any normal switch.

[Pat ondo]

Thank you,

 

I did it that way but my I am trying to get the time between the two events. I am using timer and timer interrupt. what will be the best way to do it?

[Pat ondo]

This is the code that I am using to get the time between reed sensor 1 and 2 and reed sensor 2 and 3.

 

 

#include “p24fj64ga002.h”

#include <stdio.h>

 

_CONFIG1( JTAGEN_OFF & GCP_OFF & GWRP_OFF & 

          BKBUG_ON & COE_OFF & ICS_PGx1 & 

          FWDTEN_OFF & WINDIS_OFF & FWPSA_PR128 & WDTPS_PS32768 )

 

_CONFIG2( IESO_OFF & SOSCSEL_SOSC & WUTSEL_LEG & FNOSC_PRIPLL & FCKSM_CSDCMD &  

 

OSCIOFNC_OFF &IOL1WAY_OFF & I2C1SEL_PRI & POSCMOD_XT )

 

#define XTFREQ 7372800 // On board Crystal frequency

#define PLLMODE 4 // On Chip PLL setting (Fosc)

#define FCY (XTFREQ*PLLMODE)/2 // Intruction Cycle Frequency

#define BAUDRATE 115200

#define BRGVAL ((FCY/BAUDRATE)/16)-1

 

int main(void)

{

            LATA = 0;

            LATB = 0;

 

//TRISB controls direction for all PortB pins, where 0 -> Output, 1 -> input.

TRISAbits.TRISA0 = 1;

TRISAbits.TRISA1 = 1;

TRISBbits.TRISB0 = 1;

int time1; int time2;

TMR1 = 0; TMR2 = 0;

 

// Setup Timer 1 control register (T1CON) to:

//     TON           = 1     (start timer)

//     TCKPS1:TCKPS2 = 00    (set timer prescaler to 1:1)

//     TCS           = 0     (Fosc/2)

T1CON = 0x1000;

  T2CON = 0x1000;

while(1)

{

if(TRISAbits.TRISA0 == 1) //Switch on reed 1 opens

{    

TMR1 = 0;

PR1  = 0;

if(TRISAbits.TRISA1 == 1) //Switch on reed 2 opens

{

PR1  = time1;

}

}

if(TRISAbits.TRISA1 == 1)                       //Switch on reed 2 opens

{

TMR2 = 0;

PR2  = 0;

if(TRISBbits.TRISBO == 1) //Switch on reed 3 Opens 

{

PR2  = time2;

}

}

 

}

}

 

is it the right way to write it? I want to get the time between three switches. 

[AJISH ALFRED]

Hi,

Make your code to wait till the switch open like the following;

 

while(1)

{

while (TRISAbits.TRISA0 == 0); //wait till Switch on reed 1 opens    

TMR1 = 0;

PR1  = 0;

 

while(TRISAbits.TRISA1 == 0) //wait till Switch on reed 2 opens

PR1  = time1;

 

 

while(TRISAbits.TRISA1 == 0) //wait till Switch on reed 2 opens

TMR2 = 0;

PR2  = 0;

 

while(TRISBbits.TRISBO == 0); //wait till Switch on reed 3 Opens 

PR2  = time2;

 

}

 

I hope this may work!!

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