Single Chip Solution of Pressure Transmitter, Temperature Measurement and Weighing

Pressure sensor is one of the most commonly used sensors in industrial practice and instrument control, and it is widely used in various industrial automatic control environments. The share of pressure sensor in the overall sensor market is about 21%, second only to the flow sensor, and it is the second largest type of sensor product. It involves water conservancy and hydropower, railway transportation, automatic production control, aerospace, military industry, petrochemical industry, oil well, electric power, ship, machine tool, pipeline, etc.
Recommended chip: LH32M0S Series Chip
Single Chip Solution of Pressure Transmitter, Temperature Measurement and Weighing

Linghui Lixin: pressure transmitter, single chip for temperature measurement and weighing Solution--LH32M0SXX
Linghui Lixin focuses on the development and design of high-performance analog and mixed-signal chips. The founding team members are all from well-known chip design companies, with an average design and development experience of more than ten years, familiar with product definition, design and development, testing and mass production, operation and sales and other links. The company is committed to the research and development of high-end digital-analog hybrid products. The products mainly involve high-precision signal chain and signal chain MCU/SOC. The key indicators can be compared with the leading level in the industry and can be widely used in communication equipment, industrial control, and medical equipment and automotive electronics.
The LH001-xx series ADC products launched in 2021 have been accepted by many medical and industrial customers in the measurement of ECG/EEG/DC, and become the only ADC products in China that can pass medical certification. Linghui Lixin is actively deploying ADC chip signal chain product pool and signal chain MCU product pool. At present, the second chip has been launched grandly -- the "MARS" series of cost-effective MCUs integrating 32-bit ARM® Cortex® -M0 and 24-bit ADC.
The “Mars” series MCU has gone through a strict industrial design, verification and testing process, embedded with 24-bit high-precision SD ADC, ENOB is 21.25@10hz&gain=64, typical temperature drift is 2ppm/℃, integral nonlinearity (INL ) The typical value is 5pmm, both the linearity index and the temperature drift index have filled the domestic gap in the field of integrated signal chain MCU, greatly reducing the dependence on the temperature calibration algorithm. At the same time, LH32M0S30 is embedded with rich digital peripherals including LCD, LED, SPI, I2C, UART, PWM, DMA, etc., which greatly expands the various applications of LH32M0SXX. The "MARS" chip is suitable for various application scenarios such as pressure transmitter, TC thermocouple temperature measurement, RTD temperature measurement, and weighing. Through high integration, high analog performance, and rich interface methods, SOC monolithic integration solutions can be achieved, providing customers with high-performance, simplification, low power consumption, and low-cost solutions.


Figure 1. Structural block diagram of Mars MCU

Mars-based pressure transmitter solution
Pressure sensors are one of the most commonly used sensors in industrial practice and instrumentation control, and are widely used in various industrial self-control environments. In the global market, pressure sensors account for about 21% of the overall sensor market. Second only to flow sensors, it is the second largest sensor product type. It involves water conservancy and hydropower, railway transportation, production automation, aerospace, military industry, petrochemical, oil well, electric power, ship, machine tool, pipeline and many other industries.
The traditional acquisition pressure sensor scheme is as follows:

Figure 2. Traditional pressure transmitter scheme


Linghui Lixin has launched a more minimalist solution for collecting pressure sensors as follows:

Figure 3. Mars-based pressure transmitter scheme

LM32M0SXX can collect up to 8 pressure sensing signals. It greatly simplifies the customer's design and improves the cost performance and stability of the product.

Infrared temperature measurement solution based on Mars
The new crown epidemic has quickly turned everything about medical products into hot products. All kinds of non-contact infrared human body thermometers have also become hot-selling products for epidemic prevention and control.

Figure 4. Infrared temperature measurement equipment

The basic principle of infrared temperature measurement is: use the characteristics that all objects above absolute zero will send infrared rays, choose The infrared dedicated camera sensor (infrared sensor stack) collects the infrared rays sent by the object and converts them into weak uV~mV level operating voltage data signals, and then doubles the operating voltage to become larger and enters the high-precision AD converter to obtain The digital signal is calculated through the single-chip microcomputer to obtain the specific temperature, which is displayed or output by voice or transmitted to the computer through the data information for centralized transportation according to the industrial touch screen of the man-machine interface.


The block diagram of the traditional scheme is as follows:

Figure 5. Traditional infrared temperature measurement scheme

Linhui Lixin LM32M0SXX infrared human body temperature measurement solution helps customers realize single-chip solutions.

Figure 6. Mars infrared temperature measurement scheme

The fully integrated SoC solution can save customers peripheral analog devices, improve measurement accuracy, and greatly improve the cost performance of the customer's overall solution.

Mars-based electronic weighing solution
High-precision and low-cost is the development trend of weighing instruments, which puts forward higher requirements for high-performance signal processing.
The ADC architecture of choice for scale design is the Sigma-Delta ADC because of its low noise and high linearity at low update rates.  
For the weighing system, the most important parameters are internal code, ADC dynamic input range, noise-free resolution, conversion rate, system gain, and temperature drift.

Internal code
The display resolution of scales ranges from 1:3000 at the low end to 1:10000 at the high end. For example, for a weighing instrument with a full scale of 5kg and an output display of 10,000 yards, its resolution is 0.5g, which is displayed on the LCD
is called the outer code. In order to ensure the accuracy of the outer code, a higher order of magnitude inner code is usually required as a guarantee. For example, some standard scales require an outer code whose inner code is 20 times larger, therefore, an inner code resolution of 1:200000 is required.

ADC dynamic range
The figure below shows the circuit scheme of a typical weighing instrument. When the full-scale output of the sensor is 5mV and the gain is set to 128, the input range of the ADC is 640mV. If the reference voltage is 2.5V, this means that only about 2/5 of the dynamic range of the ADC can be used. If the 640mV needs to meet the requirement of 1:200000 internal code, then the ADC needs to be able to reach the resolution of 1:781250, which requires the accuracy of 19-20 bits.

Figure 7. Circuit scheme of a typical scale

Temperature Drift
Generally, the maximum operating temperature range of weighing instruments is -10°C-50°C. A 20-bit system with a gain error of 1ppm/°C will produce an error of 50LSB in the range of 50°C. Therefore, it is also critical to choose an ADC with low gain and temperature drift.

noise-free resolution
For scale applications, the most important parameter is peak-to-peak noise, or noise-free resolution in bits. The rms noise is multiplied by 6.6 times the bit peak-to-peak noise.

Transition rate
Slew rate is also an important parameter related to system accuracy. For example, in an ADC with a conversion rate of 4Hz, the peak-to-peak resolution can reach 20.5 bits. After increasing the rate to 500Hz, the peak-to-peak resolution can only reach 16 bits. Therefore, in the application of weighing instruments, it is necessary to balance the two contradictory parameters of conversion rate and accuracy.
The LH32M0SXX series microcontrollers of Suzhou Linghui Lixin adopt high-performance 32-bit ARM® Set a low-noise programmable amplifier (PGA). It is a very suitable MCU for weighing instrument applications.  

Figure 8. Weighing instrument circuit scheme based on Mars


LH32M0SXX ADC effective number of bits (bits)

In addition, "MARS" can also be used in environmental measurement, industrial measurement, fire safety, healthcare and other fields.

Evaluation Board
48-pin and 24-pin evaluation boards, supporting circuit diagrams and reference codes are available for rapid development by customers. The compilation environment supports IAR and KEIL. All routine IAR and KEIL configurations are configured by default. Customers only need to directly open in the corresponding compilation environment to compile and burn.

Figure 9. Mars evaluation board based on different packages ( Left one: 48-pin package, right one: 24-pin package)

Mars product performance
— 32 bit ARM® Cortex® -M0 CPU
— Maximum 32MHz Working frequency
— Maximum 128 Kbytes FLASH memory
— 4 Kbytes SRAM
Clock module
— Internal 32MHz RC Oscillator (HRC), typical accuracy±1%
— Internal 32KHz RC Oscillator (LRC), typical accuracy ±10%
— 32.768KHz Low Speed Crystal Oscillator (LXT)
Working environment
— VDD Voltage: 2.2~3.6V     
— VDDA Voltage: 2.2~3.6V      
— Temperature range: -40~105℃
Power Management
— Low Power Modes: Sleep, Deep Sleep and Power Down
— Support power-on/power-down reset (POR/PDR)
— Support Low Voltage Detection (LVD)
General purpose input and output
— 35 I/O support up to 32MHz working frequency
— Support interrupt vector
High Precision Analog-to-Digital Converter (Sigma-Delta ADC)
— 24 bit High precision Sigma-Delta ADC
— Maximum support 8 external input channels
— Support single-ended and differential input
— 1/2/4/8/16/32/64/128 times optional gain
— Integral nonlinearity typical value (INL) 5ppm
— ADC channel temperature drift 2ppm/℃
— Output rate 8Hz~8kHz 
— ENOB≥19.5bit@30sps, PGA=128
— ENOB≥15.4 bit@8ksps, PGA=128
— The hardware automatically switches ADC channels, automatically polls and reads ADC data, and notifies MCU or DMA of interrupts
— With reference voltage, output 1.8/2.35/2.45/2.8V optional
— integrated temperature sensor/power supply voltage detection channel
Digital Comparator
— Fast Response Digital Comparator
LCD Driver
— Integrate 4 COM , 20 SEG Configuration
— integrated charge pump
LED Driver
— Maximum support 7 x 8 segments
One way buzzer
— 2 timers
— 4-way 16bit  advanced control timer (TIM1), 6-channel PWM  output with dead zone and complementary control
— 4-way 16bit  general-purpose timer (TIM2), with PWM  output
Programmable constant current source
— 8mA, 10mA, 12mA, 20mA
Support PWM control
OLED color screen DMA acceleration module
Serial Single Wire Debug (SWD)

— LQFP48(7mmx7mm)
— SSOP24(8.2mmx5.3mm)
— QFN48(6mmx6mm)