2.6 Low Temperature Alarm

In this project, we will make a low temperature alarm system, when the temperature is below the threshold, the Snowflake sprite will appear on the stage.

../_images/9_tem.png

Required Components

In this project, we need the following components.

It’s definitely convenient to buy a whole kit, here’s the link:

Name

ITEMS IN THIS KIT

LINK

ESP32 Starter Kit

320+

ESP32 Starter Kit

You can also buy them separately from the links below.

COMPONENT INTRODUCTION

PURCHASE LINK

ESP32 WROOM 32E

BUY

ESP32 Camera Extension

-

Breadboard

BUY

Jumper Wires

BUY

Resistor

BUY

Thermistor

BUY

You Will Learn

  • Thermistor working principle

  • Multivariable and Subtractive Operations

Build the Circuit

A thermistor is a type of resistor whose resistance is strongly dependent on temperature, more so than in standard resistors, and there are two types of resistors, PTC (resistance increases as temperature increases) and PTC (resistance decreases as temperature increases).

Build the circuit according to the following diagram.

One end of the thermistor is connected to GND, the other end is connected to pin35, and a 10K resistor is connected in series to 5V.

The NTC thermistor is used here, so when the temperature rises, the resistance of the thermistor decreases, the voltage division of pin35 decreases, and the value obtained from pin35 decreases, and vice versa increases.

../_images/7_low_temp_bb.png

Programming

1. Select a sprite

Delete the default sprite, click the Choose a Sprite button in the lower right corner of the sprite area, enter Snowflake in the search box, and then click to add it.

../_images/9_snow.png

2. Create 2 variables

Create two variables, before and current, to store the value of pin35 in different cases.

../_images/9_va.png

3. Read the value of pin35

When the green flag is clicked, the value of pin35 is read and stored in the variable before.

../_images/9_before.png

4. Read the value of pin35 again

In [forever], read the value of pin35 again and store it in the variable current.

../_images/9_current.png

5. Determining temperature changes

Using the [if else] block, determine if the current value of pin35 is 200 greater than before, which represents a decrease in temperature. At this point let Snowflake sprite show, otherwise hide.

  • [-] & [>]: subtraction and comparison operators from Operators platette.

../_images/9_show.png