#include <reg51.h>
#include <stdio.h>
 
#define ADC_CS P1_0
#define ADC_DIN P1_1
#define ADC_DOUT P1_2
#define ADC_CLK P1_3
 
sbit MPX_SEL = P2^0;
 
void delay(unsigned int count);
void send_command(unsigned char command);
unsigned char read_adc(void);
void init_serial(void);
void transmit_data(unsigned char data);
void transmit_string(char *string);
 
void main()
{
    unsigned int adc_value;
    float voltage, pressure;
    char output_string[50];
 
    init_serial();
 
    while(1)
    {
        MPX_SEL = 1; // select MPX6115A6U sensor
        delay(10);
        adc_value = read_adc();
        voltage = adc_value * 5.0 / 4096.0;
        pressure = (voltage - 2.5) * 60.0;
        sprintf(output_string, "Pressure: %.2f kPa\n\r", pressure);
        transmit_string(output_string);
 
        delay(500); // wait for half a second
 
        MPX_SEL = 0; // select ADC121C021 sensor
        delay(10);
        adc_value = read_adc();
       voltage = adc_value * 5.0 / 4096.0;
        sprintf(output_string, "Weight: %.2f kg\n\r", voltage);
        transmit_string(output_string);
 
        delay(500); // wait for half a second
    }
}
 
void delay(unsigned int count)
{
    unsigned int i;
    for(i = 0; i < count; i++);
}
 
void send_command(unsigned char command)
{
    unsigned char i;
    ADC_CS = 0;
    for(i = 0; i < 8; i++)
    {
        ADC_DIN = command & 0x80;
        command <<= 1;
        ADC_CLK = 1;
        ADC_CLK = 0;
    }
}
 
unsigned char read_adc(void)
{
    unsigned char i, adc_data = 0;
    ADC_CS = 1;
    send_command(0x81); // start conversion
    delay(1); // wait for conversion to complete
    send_command(0x01); // read conversion result
    for(i = 0; i < 12; i++)
    {
        adc_data <<= 1;
        ADC_CLK = 1;
        adc_data |= ADC_DOUT;
        ADC_CLK = 0;
    }
    ADC_CS = 0;
    return adc_data;
}
 
void init_serial(void)
{
    TMOD = 0x20;
    TH1 = 0xFD;
    SCON= 0x50;
    TR1 = 1;
}
 
void transmit_data(unsigned char data)
{
    SBUF = data;
    while(TI == 0);
    TI = 0;
}
 
void transmit_string(char *string)
{
    while(*string != '\0')
    {
        transmit_data(*string);
        string++;
    }
}