IoT temperature and humidity sensor

I just learned to draw a board not long ago, and I had other things in the middle, which delayed me a little bit. I may not be able to finish it on time, but I will not put this project down and will continue.

Production process update

2020-2-12~2020-2-25 : During this period, I mainly designed a power board to facilitate use in future competitions.

2020-2-27 : During the welding process, it was discovered that the original temperature and humidity sensor module SHT30 was in a DFN-8 package. I only had a soldering iron with a blade tip on hand, and my craftsmanship was not very good, which caused the welding to fail. Therefore, I decided to modify the temperature and humidity sensor and change it to DHT11. Temperature and humidity sensor.

2020-3-8 : After the welding is completed, it can be powered on normally, but the program cannot be burned after connecting to the computer. After checking the circuit, it was found that the two signal lines of the Micro USB and the serial port circuit are reversed.

Updated to produce V2.2 version:

• In addition to correcting the above errors;
• Change the high level of the BOOT circuit from 5V to 3.3V
• During the welding process, it was found that the GND pin of the DHT11 temperature and humidity sensor is difficult to apply tin during welding due to the large area around it connected to the copper-covered GND part. Therefore, the pad size must be increased.

Features:

The expected function is to detect the temperature and humidity in the surrounding environment, upload it through the WIFI module, and view it through the mobile phone...

function display:

To be shown...

Schematic:

Power circuit:

For good electronic products, the first thing is to have a stable power supply. Considering that this thermometer and humidity meter does not require large current to drive its work, I just started doing PCB design. For the sake of simplicity, I did not pursue low power consumption, but in order to make the system obtain Stable power supply, so the LDO linear voltage stabilization scheme is adopted, and the most commonly used AMS1117-3.3 is selected to stabilize the power supply and supply the entire circuit to work.

The power interface uses the most commonly used Micro-USB. AMS1117-3.3 uses capacitors for filtering through input and output. The capacitance values ​​adopt the recommended values ​​in the manual.

Indicating circuit:

The indication circuit is mainly used to know the operating status of the circuit. LED3 is used to indicate the power-on status. LED1 and LED2 are connected to PB14 and PB15 of STM32F103C8T6 respectively.

Button circuit:

The key circuit is not prepared for simple human-computer interaction and is reserved for backup.

Reset circuit:

The STM32F103C8T6 low-level reset is pulled up to the 3.3V voltage of the voltage stabilizing circuit through a 10K resistor. The 0.1uF capacitor is used for filtering to prevent the chip from being reset due to interference.

BOOST circuit:

BOOT determines the startup location of the chip program

Convert to serial port circuit:

In order to simplify the circuit and save costs, the debugging interface is abandoned and the serial port is used to download the program to the chip. Therefore, a USB to serial port circuit is needed.

Crystal circuit:

Use an external passive crystal oscillator to provide clock signals to the chip

Main control circuit:

The main control uses STM32F103C8T6. There are four distributed power supplies on the chip, so four filter capacitors are used.

WB3S circuit:

The Tuya module here is only for communication, so after powering the module, only one of the serial ports is led out to the microcontroller.

Temperature and humidity sensor circuit:

The temperature and humidity sensor uses DHT11.

Display circuit:

A lower-cost OLED screen is used to display temperature and humidity information.

Programming ideas:

Summarize: