KY-028 Temperature sensor (thermistor)

This module contains an NTC thermistor, which can measure temperatures in the range of -55°C up to +125°C. The resistance value of the thermistor decreases with increasing temperatures.

Note on use

This sensor is ideally suited for threshold measurement. This means that the sensor emits a digital high signal as soon as a threshold value set by the user is exceeded. However, this also means that the analog measured values are not suitable for conversions, as the analog signal is also influenced by the rotary potentiometer.

Digital output: If a temperature is measured above a limit value, this is output here - the limit value can be set using the potentiometer.

Analog output: Direct measured value of the sensor unit

LED1: Indicates that the sensor is supplied with voltage.

LED2: Indicates that the limit value has been exceeded

Functionality of the sensor

This sensor has three functional components on its circuit board: The front sensor unit, which physically measures the environment and outputs it as an analog signal to the second unit, the amplifier. This amplifies the signal depending on the resistance set on the rotary potentiometer and sends it to the analog output of the module.

Here it is to be noted: The signal is inverted. If a high value is measured, this results in a lower voltage value at the analog output.

The third unit represents a comparator, which switches the digital output and the LED when the signal falls below a certain value. This value (and thus the sensitivity of the module) can be adjusted via the rotary potentiometer:

Pin assignment

Code example Raspberry Pi

Pin assignment Raspberry Pi

Analog sensor, therefore the following must be considered: The Raspberry Pi has, in contrast to the Arduino, no analog inputs or there is no ADC (analog digital converter) integrated in the chip of the Raspberry Pi. This limits the Raspberry Pi, if you want to use sensors, which do not output digital values, but a continuously changing value (example: potentiometer -> different position = different voltage value).

To avoid this problem, our sensor kit X40 contains the KY-053, a module with a 16-bit ADC, which you can use on the Raspberry to expand it with 4 analog inputs. This module is connected to the Raspberry Pi via I2C, takes over the analog measurement and transfers the value digitally to the Raspberry Pi.

So we recommend to connect the KY-053 module with the mentioned ADC in between for analog sensors of this set. You can find more information on the KY-053 Analog Digital Converter information page.

The program uses the corresponding ADS1x15 and I2C Python libraries from Adafruit to control the ADS1115 ADC. These have been published at the following link https://github.com/adafruit/Adafruit_CircuitPython_ADS1x15 under the MIT license. The required libraries are not included in the download package below.

The program reads the current values of the input pins and outputs them to the console as a value in [mV].

Please note that you need to enable I2C on your Raspberry Pi before using this example.

#!/usr/bin/python
# coding=utf-8

import time
import board
import busio
import adafruit_ads1x15.ads1115 as ADS
from adafruit_ads1x15.analog_in import AnalogIn
import RPi.GPIO as GPIO
GPIO.setmode(GPIO.BCM)
GPIO.setwarnings(False)
# Create the I2C bus
i2c = busio.I2C(board.SCL, board.SDA)

# Create the ADC object using the I2C bus
ads = ADS.ADS1115(i2c)

# Create single-ended input on channels
chan0 = AnalogIn(ads, ADS.P0)
chan1 = AnalogIn(ads, ADS.P1)
chan2 = AnalogIn(ads, ADS.P2)
chan3 = AnalogIn(ads, ADS.P3)

delayTime = 1
Digital_PIN = 24

GPIO.setup(Digital_PIN, GPIO.IN, pull_up_down = GPIO.PUD_OFF)

while True:
    analog = '%.2f' % chan0.voltage
 
    # output to console
    if GPIO.input(Digital_PIN) == False:
        print ("Analog voltage value:", analog, "V, ", "Limit: not yet reached")
    else:
        print ("Analog voltage value:", analog, "V, ", "Limit: reached")
    print ("---------------------------------------")
 
    # reset + delay
    button_pressed = False
    time.sleep(delayTime)

Sample program download

KY028-RPi.zip