#9th LCSC Electronics Contest# Multifunctional Environmental Monitoring Instrument

1. Project Function Introduction

This project is based on the STM32G030K6T6 and utilizes the Sensirion SHT40 temperature and humidity sensor module to achieve temperature and humidity detection, realizing real-time temperature and humidity detection and Bluetooth monitoring. If the detector is not operated for a period of time, the chip will enter a stop mode to ensure low-power operation.
2. Hardware Design

The main control chip selected is the STM32G030K6T6.
Since all components are powered by 3.3V, and the power supply is two 3.7V 14500 batteries, the 7.4V power supply needs to be stepped down. The LM1117S is selected for step-down, and the power supply and step-down module circuit is as follows.
Considering that the chip needs to achieve low-power operation, the RTC needs to be enabled to ensure time accuracy; therefore, an external crystal oscillator is used, and its circuit is as follows
. Simultaneously, a wake-up button is needed to switch the chip from stop mode to run mode.
The SHT40 temperature and humidity sensor module circuit uses IIC communication with the MCU, where the SDA and SCL lines need to be connected to pull-up resistors.
To achieve program download, the SWD download and debugging interface circuit is as follows
. A user-defined button is provided, which I define here as page scrolling up and down, and confirm and cancel.
To store temperature and humidity data and character data, an EEPROM is required. Note that the EEPROM communicates with the MCU via IIC, therefore pull-up resistors are needed for the SDA and SCL lines.
A 1.8-inch TFT screen is used for the LCD, which communicates with the MCU via SPI. The circuit is as
follows: To allow the LCD to turn off in MCU stop mode, I added a latching switch between the power supply and the LCD's VCC pin. However, this was found to be unnecessary, as the screen can be turned on/off by changing the level of the backlight pin (BL). Therefore, the latching switch can be removed. During subsequent debugging, it was found that the LCD screen can still light up without VCC power, but the brightness is dim. Therefore, if the application scenario is at night and the screen brightness is a concern, the latching switch can be retained.
To enable communication with the mobile app, a Bluetooth module is added. The Bluetooth module used is a 6328A serial Bluetooth module, part number C20539408. Since there was no model in the EDA for this Bluetooth module, I used a 1x5pin header instead. Also, because the Bluetooth module uses a stamp-hole connection, the model in the EDA could be changed to a surface mount design, thus reducing the height of the Bluetooth module and allowing more height for the LCD screen, thereby reducing the overall thickness of the temperature and humidity sensor.
Finally, to test and monitor the MCU's operating status, an LED was added.
During the PCB design, to reduce electromagnetic interference and the impact of the manufacturing process, the copper plating at the bottom of the crystal oscillator and any sharp-shaped copper areas needed to be removed by setting forbidden areas
. The final circuit board and related components are shown in Figure
3. The software design

 defines the chip pins as follows
. To ensure the RTC operates normally, the RCC needs to be configured first, and the LSE set to an external crystal oscillator
. Next, the RTC needs to be configured, including the time representation method (binary/BCD) and the initial time.
Other methods such as I2C, SPI, and USART can be implemented by referring to various tutorials.
It is particularly important to note that although the LCD screen uses SPI communication, it is actually level-controlled; therefore, the pins do not need to be defined as SPI mode.
The code writing section first needs to implement the page display, including the date, time, current temperature and humidity, Bluetooth status, and power supply voltage
. The date and time modification interface implements functions such as time modification and cursor blinking. The rules are: the last two digits of the year, month, date, hour, and minute can be changed. Pressing the UP/DOWN button without any operation will switch to page 0. The first press of the CONFIRM button locks the YEAR value; pressing the UP/DOWN button again will change the YEAR value. Pressing the CONFIRM button again will move the cursor to the next value. Press the CANCEL button to adjust the end date and time.
To further reduce MCU power consumption (the MCU current is in the mA range in sleep mode, while it is only in the uA range in stop mode), the MCU will enter stop mode after the detector has been inactive for 10 seconds. To exit stop mode, the MCU can be woken up by pressing the wake-up button. It is important to note that when the MCU enters stop mode, the chip's HSI clock will stop and switch to the LSE clock. Therefore, in addition to waking up the MCU, the RCC needs to be reconfigured to prevent timing errors in the tick timer.
Since Bluetooth is a serial Bluetooth, only the printf function needs to be redefined.
In addition, it is important to note that when using printf, please check "Use MicroLIB" in the magic wand; otherwise, printf will not work.
Bluetooth APP design uses MIT App Inventor, which is an APP design webpage with the URL http://app.gzjkw.net/.
Draw the APP interface
and write the APP backend code.
4. Physical demonstration

 : Power on the temperature and humidity detector and get the following interface.
Press the left up and down keys to enter the date and time setting interface. Press the OK/Cancel key in the upper right corner and the left up and down keys to increase or decrease the time.
After setting, press the left up and down keys to switch to the temperature and humidity detection interface. You can see that the time has been successfully set.
Open the mobile Bluetooth APP
and select the Bluetooth device.
When Bluetooth is successfully connected, the Bluetooth module's connection indicator light will light up, and the data display interface will also show that Bluetooth is connected.
Click the query button to query the current temperature and humidity.
5. Attachment Descriptions

: MyProject.rar: Project source code files.
SPI LCD source code and HAL library project.rar: 1.8-inch LCD screen driver (including 51 microcontroller and STM32F1 series microcontrollers; other series can be ported using this).
base.apk: Bluetooth APP for this project.
83991-1.8-inch IPS+LCD module information.rar: 1.8-inch LCD screen driver and Chinese character encoding software.
6. Demo video:

https://www.bilibili.com/video/BV1AsezefEFf/?share_source=copy_web&vd_source=1cc6752786a7dd940c6c809a85212bba