This code implements the functionality of reading a temperature sensor...

September 1, 2025 at 04:09 PM

#include <xc.h>
#include <stdio.h>
#include "mcc_generated_files/mcc.h"

// Assume 20 MHz crystal
#define _XTAL_FREQ 20000000

// SSD digit control pins
#define DIGIT1 LATCbits.LATC0
#define DIGIT2 LATCbits.LATC1

// Buttons
#define STORE_BTN PORTDbits.RD0
#define READ_BTN  PORTDbits.RD1

unsigned int readADC(void) {
    ADCON0bits.GO = 1;
    while(ADCON0bits.GO);
    return ((ADRESH<<8) + ADRESL);
}

int readTemperature() {
    unsigned int adc_val = readADC();
    float voltage = (adc_val * 5.0) / 1024.0;
    int tempC = voltage * 100;   // LM35 => 10mV per °C
    return tempC;
}

void displayNumber(int num) {
    int tens = num / 10;
    int ones = num % 10;
    
    // Multiplexing
    DIGIT1 = 1;
    sendToSSD(tens);
    __delay_ms(5);
    DIGIT1 = 0;
    
    DIGIT2 = 1;
    sendToSSD(ones);
    __delay_ms(5);
    DIGIT2 = 0;
}

void main(void) {
    SYSTEM_Initialize(); // MCC init
    int temp;

    while(1) {
        temp = readTemperature();
        displayNumber(temp);

        if(STORE_BTN == 0) {
            saveToSD(temp);
            __delay_ms(500);
        }
        if(READ_BTN == 0) {
            int last = readFromSD();
            displayNumber(last);
        }
    }
}

This code implements the functionality of reading a temperature sensor using an ADC, displaying the read temperature on a 7-segment display, and interacting with the user via buttons to store or retrieve a temperature value. Below is a breakdown of what the code does:

1. Initial Setup:

The code configures the ADC (Analog-to-Digital Converter) and digital I/O pins through the SYSTEM_Initialize() function (called at the start of main).
It uses a 20 MHz crystal oscillator (#define _XTAL_FREQ 20000000) to calculate delays and timing.

2. ADC Conversion:

The readADC() function performs an analog-to-digital conversion by triggering the ADC (ADCON0bits.GO = 1) and waits until the conversion is complete.
The ADC result is returned as a 10-bit value by combining the high (ADRESH) and low (ADRESL) register contents ((ADRESH << 8) + ADRESL).

3. Temperature Reading:

The function readTemperature() calculates the temperature in °C based on the ADC conversion result.
- It assumes the use of an LM35 temperature sensor, which outputs 10 mV per degree Celsius.
- The ADC result is converted into a corresponding voltage and then multiplied by 100 to determine the temperature in °C.

4. Displaying the Temperature:

The displayNumber() function handles the multiplexed display of two digits on 7-segment displays.
It splits the input num into its tens and ones place values.
It sequentially activates one display (DIGIT1 or DIGIT2), sends the appropriate digit using a function sendToSSD() (presumably translating the digit into segment control signals), and then disables the display before moving to the next digit.
A short delay (__delay_ms(5)) ensures stable display timing via persistence of vision.

5. Button Functionality:

The main loop (while(1)) checks for button presses to perform specific actions:

STORE_BTN (button connected to PORTDbits.RD0):
- If pressed (STORE_BTN == 0), the current temperature is stored by calling the saveToSD(temp) function (presumably saving data to an SD card or similar storage device). A delay of 500 ms is applied to debounce the button.
READ_BTN (button connected to PORTDbits.RD1):
- If pressed (READ_BTN == 0), retrieves the last stored temperature using readFromSD() and displays it on the 7-segment display.

6. Repetition:

The loop continues indefinitely to continuously read, display, and respond to button inputs.

Notes:

Functions like sendToSSD(), saveToSD(), and readFromSD() are not provided in the code, but they are assumed to handle the task of sending digits to the 7-segment display and interacting with storage (e.g., SD card).
Multiplexing is handled efficiently by activating and deactivating the relevant digit control pins (DIGIT1 and DIGIT2) and updating the displayed content rapidly.

Summary of Functionality:

Reads temperature from an LM35 sensor.
Displays temperature on a 2-digit 7-segment display using multiplexing.
Allows storing and retrieving a temperature value using two buttons.
Handles timing and debouncing.

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