Highly sensitive indoor formaldehyde detector solution

An Introduction:
This detector uses a 32-bit ultra-low power EFM32TG840F16 microprocessor and a high-sensitivity formaldehyde sensor CH20/S-10 to realize the signal processing and sampling of formaldehyde concentration. The system has an external communication interface and necessary extended function modules to build an intelligent, multi- Functional detection system. The hardware of the formaldehyde detector is mainly composed of a single-chip microcomputer main control system, a formaldehyde sensor interface, a liquid crystal display (LCD), a functional keyboard, data storage, printing and alarm output and other functional modules. The system uses 32-bit EFM32TG840F16 single-chip microcomputer as the main control core, embedded 16KB Flash program memory and 4KB RAM, up to 160 segments of LCD drivers (maximum 8COM drive, support for animation, flashing and other special effects), 8-channel/12-bit ADC ( Support hardware oversampling), 2 USART (support SPI\UART\I2S), 1 LEUART, 1 LESENSE (support resistance, inductance, capacitive signal detection), 3 operational amplifiers, hardware encryption and decryption AES, 2 12 Bit DAC and a large number of I/O ports, etc., fully meet the functional requirements of this formaldehyde detector. The main features of this chip are: low voltage (1.85 ~ 3.8V), low power consumption (only 0.9uA in EM2 mode), 32-bit instructions, high performance (based on Cortex-M3 core), extremely low operating power consumption, Fast wake-up time, powerful functions, high noise immunity (unused pins are disconnected from the MCU), peripherals can work autonomously (mainly due to DMA and PRS peripheral reflection systems) and ultra-energy-saving (ADC: 12bit, 1Msps, only 350uA; Analog Comparator: only 100nA; LCD: local power consumption 0.55uA; LEUART: only 150nA at 9600 baud rate; AES: 128/256bit encryption/decryption only requires 54/75 cycles) , Easy to be intelligent and portable. Moreover, a complete set of supporting development tools such as the development board has a real-time monitoring function of current, which can locate the code position, which is convenient for engineers to optimize the code in time to save energy.

Program features:
Formaldehyde sensor interface module
The sensor interface module is composed of CH20/S-10 formaldehyde sensor, I/V converter RCV420 and so on. The formaldehyde sensor consists of a formaldehyde probe and a CH20 sensor. When the indoor formaldehyde gas is absorbed by the internal sampling system, a current value proportional to the concentration of formaldehyde is generated. Because the single-chip A/D samples the voltage value, and the detected value is the trace current value; therefore, the current value needs to be amplified and converted Is the corresponding voltage value. The integrated I/V converter RCV420 is used to convert the current value into a corresponding voltage of 0 ~ 3.6V, and send it to the A/D conversion interface ADC of EFM32TG840F16 to realize the detection of the concentration signal. The single-chip microcomputer performs calculation and processing, looks up the table and segmentally linearizes the processing results and range, and completes the sensor signal corresponding to the level of concentration. The RCV420 in the system has the functions of precision operational amplifier and resistor network, which can convert the 4-20mA loop current into a 0-3.6V voltage. Without external adjustment, it can obtain a common mode rejection ratio of 86dB. It has high performance and resistance. Interference ability.
Data storage and printing module
Extend 2KB of E2PROM outside EFM32TG840F16 (on-chip flash emulation EEPROM can also be used), and connect to EFM32TG840F16 data port through I2C bus to store the sampled formaldehyde concentration data for printer printing. The printer interface circuit is directly connected to the microprocessor through the RS-232 serial port, and the formaldehyde concentration value is printed out by using the software setting method.
Keyboard and display module
The system is connected to an external keyboard and LCD display device to realize the man-machine dialogue function. The keyboard is set to 3?3 array keyboard, with function selection key, OK key, alarm confirmation and printing key, complete density display, data query, printing and power on/off functions. The microprocessor EFM32TG840F16 contains an LCD drive circuit, which can drive a 160-segment LCD with ultra-low power consumption, which is especially suitable for use in portable instruments. The user can read the detection density value, print and set related functions and other information through the LCD display.
Other modules

The power supply voltage of this system is 3V, and it uses two batteries to supply power, and it can also be connected to an external 3V DC power supply. The system clock is provided by an external crystal oscillator. In order to meet individual needs, a buzzer alarm circuit is also added.

Industry Classification: Test Equipment

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