Product Overview

The MEMSF MTP40-D is an NDIR (Non-Dispersive Infrared) CO2 sensor module designed by Shenzhen MemsFrontier Electronics Co., Ltd. It features advanced self-calibration algorithms enabling long-term high accuracy without factory recalibration.

Specifications

• Target Gas: CO2
• Measurement Range: 400 ppm to 5000 ppm
• Accuracy: ±(50 ppm + 5% of reading)
• Response Time: T90 = 90 seconds
• Operating Temperature: -20°C to 60°C
• Operating Humidity: 0-90% RH (non-condensing)
• Storage Temperature: -40°C to 85°C
• Power Supply: 4.2V to 5.5V
• Power Consumption: Peak 300mA, Normal 4mA, Average 13mA
• Dimensions: 32.5 × 20 × 8.5 mm (max)
• Communication Interfaces: UART and I2C
• Life Expectancy: Over 10 years

Pin Configuration and Electrical Characteristics

The module has 9 pins including power supply, ground, communication lines (Host-TX, Host-RX for UART; I2C SDA, SCL), PWM output, alarm output, and manual calibration input (bCAL-in).

• Output Voltage: 3.3V ±2%
• Maximum Output Current: 6mA
• Alarm Output: Open-drain with weak pull-up (~50kΩ), outputs high when CO2 >1000 ppm, low when <800 ppm
• Manual Calibration Pin (bCAL-in): Pull low for >2 seconds to trigger manual calibration using ambient CO2 (~400 ppm)

Operating Principles and Features

The sensor uses NDIR technology for CO2 detection. It includes a self-calibration algorithm with a default cycle of 7 days (adjustable from 24 to 720 hours). After power-on, an initial self-calibration occurs within 24 hours to quickly stabilize accuracy. For best results, the sensor environment should approximate outdoor atmospheric CO2 levels for several hours during calibration periods.

Communication Protocol

The module supports UART and I2C communication at 9600 bps. The communication protocol uses a fixed frame header (0x42 0x4D) and includes instruction bytes, command bytes, data length, data payload, and checksum for error checking.

• Key Commands:
• Set air pressure parameter (default 1013 hPa)
• Read air pressure
• Single point correction (manual calibration)
• Read calibration status
• Read CO2 concentration
• Enable/disable self-calibration
• Read/set self-calibration period

The CO2 concentration data is transmitted as a 32-bit integer with a validity flag (0x00 valid, 0xFF invalid).

Calibration Methods

• Self-Calibration: Automatic periodic correction to maintain accuracy, default cycle 7 days, adjustable via commands.
• Manual Calibration: Triggered by pulling bCAL-in pin low for more than 2 seconds in an environment with ambient CO2 (~400 ppm). Also supported via software commands.

Alarm Function

The Alarm-OC pin outputs a high level when CO2 concentration exceeds 1000 ppm and low when below 800 ppm. It is an open-drain output with a weak pull-up resistor and cannot sink current. In case of module error, the alarm pin remains high.

PWM Output

The PWM output cycle is 1004 ms with a high pulse width ranging from 2 ms to 1002 ms corresponding to CO2 concentration from 0 to 5000 ppm. The CO2 concentration can be calculated using the formula:

Cppm = 5000 × (TH - 2 ms) / (TH + TL - 4 ms)

where TH is the high-level duration and TL is the low-level duration within one PWM cycle.

Application Examples

Examples include setting and reading air pressure parameters, reading CO2 concentration, and controlling calibration functions via serial commands. The document provides detailed hexadecimal command frames for these operations.

Important Notes and Best Practices

• Ensure the sensor environment approximates outdoor CO2 levels during calibration periods for accurate self-calibration.
• Do not connect pull-up or pull-down resistors to the RS485 direction control pin (Pin 8) when used in UART mode.
• The alarm output pin has limited drive capability; external circuitry should accommodate this.
• Communication lines operate at 3.3V logic levels with internal current limiting resistors.

Manufacturer Contact

Shenzhen MemsFrontier Electronics Co., Ltd.
Address: 3/F, B2 Building, China Merchants Guangming Sci-Tech Park, Guanguang Rd., Guangming District, Shenzhen, Guangdong, China 518107
Tel: +86-755-21386871
Email: [email protected]
Website: www.memsf.com