carbon monoxide alarm

Introduction

The main function of this module is to detect the carbon monoxide content in the environment. When it exceeds the set value, it will alarm through a buzzer to indicate that the CO content in the air is too high. The design is simple and works stably in complex environments.

Hardware introduction:    Main control chip: ESP12F Manufacturer: Anxinke Purpose: networking and accepting and processing control commands

                     LDO chip: ADP151AUJZ-3.3-R7 Manufacturer: ADI Purpose: Convert 5V input voltage to 3.3V

                     CO sensor: MQ-7 Manufacturer: Winsen Purpose: Measure CO content in the air

                     Digital tube driver: MAX7219 Manufacturer: MAXIM Purpose: drive 2X4-digit digital tube

                     Four-digit digital tube: FJ5461AS Manufacturer: ReliaPro Purpose: Display the CO content in the air and the set threshold

Software introduction: The programming software of the main control chip is Arduino IDE, which supports programming, downloading and serial port monitoring functions, and has a friendly interface.

                 PCB and schematic diagrams are drawn by Lichuang EDA, which is free and stable; it also comes with a large number of component libraries.

Schematic introduction

Power supply: Micro USB power supply, the power supply voltage is 5V, and ADI's ADP151AUJZ-3.3-R7 is used for step-down conversion. The ADP151 is an ultralow noise, low dropout linear regulator that operates from 2.2 V to 5.5 V and delivers up to 200 mA of output current. In the input and output parts, 1UF capacitors in 0805 packages are used for rectification, and the official recommended circuit is used:

CO detection sensor: Use the MQ-7B gas sensor manufactured by Winsen. The gas-sensitive material used in the MQ-7B gas sensor is tin dioxide (SnO2) with low conductivity in clean air. The high and low temperature cycle detection method is used to detect carbon monoxide. The conductivity of the sensor increases as the concentration of carbon monoxide gas in the air increases, and the content can be easily detected through the MCU.

Four-digit digital tube: Use the four-digit digital tube model FJ5461AS, the manufacturer is ReliaPro, and the common cathode four-digit digital tube.

Digital tube driver chip: This design uses the MAX7219 driver chip. MAX7219 is a multi-bit LED display driver launched by the American MAXIM company. It uses a 3-wire serial interface to transmit data and can be directly connected to the microcontroller interface. Users can easily modify its internal parameters. To achieve multi-digit LED display. It contains hardware dynamic scanning circuit, BCD decoder, segment driver and bit driver. The connection schematic diagram is shown in the figure:

software part

The software part is relatively simple. You only need to follow the communication timing of MAX7219 in the chip manual and send the value to be displayed. The following picture is the MAX7219 timing diagram:

Follow the diagram and follow the steps in the arduino IDE to pull up and down the corresponding PIN. The picture shows a sub-function for writing data:

To obtain the CO content in the air, you only need to use the ADC to read the voltage value of the sensor. In the arduino IDE, you only need one line of commands: analogRead (the PIN number of the sensor connection);

Other parts only need to use if judgment to realize all functions.

Other scenarios:

The detection port of the detection board is designed to be detachable and can be replaced with other sensors as needed to detect various gases, such as MQ-2 to detect gas, etc.....

Actual picture: front

Problems encountered

A simple hands-on training project with relatively low difficulty. Basically, no problems have been encountered. It should be noted that the sensor needs 60 seconds to warm up when working. It will heat up during normal working hours. Don’t worry, when using it Need to be as close as possible to the likely source to provide better detection.

Experience

• I am still very grateful to Lichuang EDA and Anxinke for organizing this event. I learned a lot and was very satisfied.
• I am also very grateful to the various libraries provided by various open source platforms. The predecessors planted trees for future generations to enjoy the shade, which provided great help to the functions of the project. Like it.
• There are many big names and many good projects in the open source platform. I am very happy to learn in this environment. I love it.
• A very good event, I hope to hold it again in the future.