Grove-Temperature Sensor V1.2 and M5StickC

Products & Technology Grove
#1

I bought the Grove-Temperature Sensor V1.2 and connected to M5StickC (https://m5stack.com/products/stick-c). I copied almost all the code from the specs page to convert the analog read to actual temperature, only adding the #include <M5StickC.h> and the M5.begin, but the temperature is way off and very oscillating. I am using pin 32 to read the data, Is it correct? Is it a sensor issue?

For example, a sample output is:

42.42
44.15
42.42
42.85
42.96
45.96
46.07
44.38
44.15
42.74
43.50
42.42
44.15
44.49
42.42
45.16
49.58
42.85

And the code is:

#include <M5StickC.h>
#include <math.h>

const int B = 4275; // B value of the thermistor
const float R0 = 100000;
const int PIN = 32;

void setup() {
M5.begin();
Serial.begin(9600);

}

void loop() {

int a = analogRead(PIN);

float R = 1023.0/a-1.0;
R = R0*R;

float temperature = 1.0/(log(R/R0)/B+1/298.15)-273.15; // convert to temperature via datasheet

Serial.println(temperature);
delay(500);
}

Thanks,
Fernando Gonzalez Sidders

#2

Sorry, we are not familiar with M5stack. This code is strange. This sensor only use the analog interface. M5.begin(); What does it do here?

#3

I solved the issue, I am getting the correct temperature now.

I changed the code to:

#include <M5StickC.h>
#include <math.h>

const int B = 4275;
const float R0 = 100000;
const int PIN = 33;

void setup() {
M5.begin();

Serial.begin(115200);

}

void loop() {

int a = analogRead(PIN);

float R = 4095.0/a-1.0;
R = R0*R;

float temperature = 1.0 / (log(R / R0) / B + 1 / 298.15) - 273.15;

Serial.println(temperature);

delay(500);
}

The correct pin was 33, and modified the 1023.0 to 4095.0 in the formula because esp32 is returning values between 0 and 4096. But anyway, the temperature readings were too high. Then, I modified the grove cable (as is explained here https://tinkerfarm.net/projects/the-m5stickc/the-5-volt-danger-with-the-m5stickc/) feeding the temperature sensor with 3.3v instead of 5v. And, now, (with no additional code changes) the temperature is correct.

Thanks,
Fernando