Design of digital barometer based on MPX4105

The microcontroller can not only be used to measure temperature, but also to measure non-electrical signals such as air pressure, which requires the use of air pressure sensors. The principle of the air pressure sensor is to convert air pressure information into current or voltage output. The converted voltage or current is often an analog signal, so A/D conversion must also be performed to meet the interface requirements of the microcontroller. After learning the use of temperature sensors, combined with the MPX4105 air pressure sensor, we learned the design of a digital air compressor.

 

Main components:

1. AT89C52 single-chip microcomputer chip collects, controls and processes the air pressure information of the sensor.

2. MPX4105 integrated pressure sensor.

3. The voltage/frequency converter is LM331 high-precision V/F conversion chip.

4. The three-terminal low current linear voltage regulator chip MC78L05 outputs a stable +5v voltage.

 

Test flow chart: 

Test circuit diagram: 

Test program code:

//DigAirPress.h program

#ifndef _DIGAIRPRESS_H // Prevent DigAirPress.h from being referenced repeatedly

 

#define _DIGAIRPRESS_H

 

#include // Reference the header file of the standard library

#include

#include

#include

 

#define uchar unsigned char

#define uint unsigned int

 

#define K 2000 // K is the V/F conversion gain constant

 

uchar PressVal; // pressure value

uchar count; // counter

 

#endif

 

// DigAirPress.c program

#include "DigAirPress.h"

 

void display();

 

/* Timer 0 interrupt */

void timer0() interrupt 1 using 1

{

       uint x,y;

       uint fo;

 

       ET0 = 0; // Disable timer 0 interrupt

       count++;

       if (count == 10) // 500ms

       {

              TR1 = 0; // Stop counter 1

              count = 0;

              x = TH1;

              y = TL1;

             

              /* Calculate the frequency value. Since it is 500ms, multiply it by 2 */

              fo = (x*256+y)*2;

             

              /* Calculate the air pressure value according to the calculated formula P=20fo/K+9 */

              PressVal = (uint)(20*(float)(fo)/K+9);     

 

              /* Display function, display the calculated PressVal value through a 5-digit digital tube (4 digits and 1 decimal point)

              Displayed, the display precision is 0.1, that is, retain one decimal place. This function is omitted in this example. */     

              display();

             

              /* Clear counter 1 to 0 */

              TH1 = 0;

              TL1 = 0;          

    }

 

       /* Reset TH0 and TL0 */

       TH0 = -50000/256;

       TL0 = -50000%256;

 

       ET0 = 1; // Enable timer 0 interrupt

       TR1 = 1; // Start counter 1

 

       return;

}

 

/* Main program */

void main(void)

{

       EA = 1;

       ET0 = 1; // Enable timer 0 interrupt

      

       /* Set T1 to 16-bit counter and T0 to 16-bit timer */

       TMOD = 0x51;

      

       /* Timer 0 is 50ms timing */

       TH0 = -50000/256;

       TL0 = -50000%256;

      

       /* Timer 1 starts counting from 0 */

       TH1 = 0;

       TL1 = 0;

 

       TR0 = 1; // Start timer 0

       TR1 = 1; // Start counter 1

 

       count = 0;

      

       /* Start an infinite loop and wait for an interrupt to arrive */

       while (1);             

 

}

 

void display(void)

{

       //Omitted in this example

}