16x2 lcd screen crashes after a while

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1

I have built a simple temperature reader using Arduino UNO, and a NTC thermistor. It basically reads the voltage across the thermistor and converts into temperature. I also used an external volage reference IC. Internal interrupt is used to sleep the CPU during the measurement. Everything works well for a while, then LCD crashes and displays random characters. I am seeking help. I have checked the wiring, but everything been correct. External 9V-1A power supply is used.

Here is the sketch:

#include <avr/sleep.h>
#include <LiquidCrystal.h>
#include <math.h>

int const aREF = 0b00000000;
int ThermistorPin = 0;
int Vo;
float R1 = 20000;
float logR2, T, Tc, Vo_2, R2;
float c1 = 1.129241e-03, c2 = 2.341077e-04, c3 = 0.087755e-06;
LiquidCrystal lcd(12, 11, 5, 4, 3, 2);

void setup() {
ADMUX = aREF;
ADCSRA |= 1 << ADEN;
ADCSRA |= 1 << ADIE;
ADCSRA |= ((1 << ADPS2) | (1 << ADPS1) | (1 << ADPS0)); // Corrected ADPS setting
sleep_enable();
set_sleep_mode(SLEEP_MODE_ADC);
analogReference(EXTERNAL);
lcd.begin(16, 2); // Initialize LCD
}

void loop() {
sei();
sleep_cpu();
Vo = analogRead(ThermistorPin);
Vo_2 = ((float)Vo / 1023.0) * 5.0;
R2 = R1 * ((5.0 - Vo_2) / Vo_2);
logR2 = log(R2);
T = (1.0 / (c1 + c2 * logR2 + c3 * logR2 * logR2 * logR2));
Tc = T - 273.15;

lcd.setCursor(0, 0); 
lcd.print("Temp = ");
lcd.print(Tc);
lcd.print(" C");

delay(500);
lcd.clear();

}

ISR(ADC_vect) {}

2

What the point to sleep cpu in fraction of the millisecond during the ADC if you have a delay 500 ms in your CPU active state?

Remove all sleeping code from the sketch and test how it works. "Keep it clean and simple"

3

Search for "ratiometric".
If you power the NTC + resistor with the 5V pin and use the default reference of the 5V, then you get the maximum accuracy.
With averaging/oversampling you can get a higher resolution.
If the NTC has a datasheet with a table, then you get the best accuracy.

Can you show a photo, so we can see the wiring and the display ?

I made the circuit in Wokwi simulation. Wokwi has a common NTC module with a 10k resistor. I can not get the right temperature.

After starting the simulation, click on the NTC module to change the temperature.

4

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5

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