Design of a micro urine analyzer based on NXP LPC2148

Urine analyzer is a medical instrument that determines human health by detecting relevant components in human urine. It uses non-invasive and non-invasive detection methods and can effectively check physical conditions.

Project Overview

The miniature urine analyzer we designed can detect ten parameters of urine, including white blood cells, nitrite, urobilinogen, protein, pH value, occult blood, specific gravity, ketone bodies, bilirubin and glucose.

After the user puts the test strip soaked in urine into the instrument, the LED light source is controlled by LPC2148 to emit light in time, and then the reflected light is irradiated to the CCD through the optical fiber. After signal acquisition and analog-to-digital conversion, and after the normalization algorithm in the microprocessor, the result is output to the LCD for display, or transmitted to the PC as needed. The Ethernet interface can be used to connect to the Internet, which is convenient for building a health detection network. You can get a doctor's diagnosis without complicated operations, which is very suitable for home users.

By designing a new instrument structure and detection method, the accuracy of the instrument reaches or exceeds the level of urine analyzers commonly used in domestic hospitals, and the volume is reduced to about 170×110×120mm, and the time used for one measurement is controlled within 10 seconds. Users can perform intuitive operations through the touch screen, or ask doctors to diagnose urine analysis results through the computer network. Ultimately, a health detection network integrating individuals, instruments, and medical institutions will be realized.

System implementation principle

Urine contains a variety of substances that characterize human health. When a specially designed test strip is immersed in urine, the substances in different areas of the test strip will react with the corresponding components in urine and show different colors. After the LED shines light on the test strip, the spectrum and intensity of the reflected light will also be different due to the different colors of different areas on the test strip. Using CCD to detect the intensity of the reflected light transmitted through the optical fiber, the color information of the test strip can be obtained, thereby identifying the components of urine and obtaining health information of the human body.

The embedded urine analyzer system mainly includes 8 functional parts, including the main controller, power supply and reset, LCD touch screen, photoelectric detection module, LED, CPLD, CCD, USB and Ethernet. The main controller chip adopts the highly integrated LPC2148 microprocessor. The USB controller integrated in the chip can be used for power supply and data transmission. The internal integrated ADC can process the analog signal collected by the CCD. The internal integrated PWM function is used to drive the LED. Other general I/O ports are used to control the LCD touch screen, Ethernet and other related modules. Only a few chips are added to the LPC2148 to realize the functions of the system, which reduces the volume and power consumption.

Hardware Platform Detail

Figure 1 Hardware design block diagram

Hardware Module Description

The hardware part of the embedded micro urine analyzer system is mainly composed of a photoelectric detection module, an embedded main control module, an LED light source module, and a CCD module. The main control module controls the other three modules to work together to realize the functions of the instrument.

The embedded main control module uses the microcontroller LPC2148 based on the ARM7TDMI-S core, which has a very high degree of integration. It has 40kB of on-chip static RAM and 512kB of on-chip Flash memory, and integrates ADC, DAC converter, watchdog, real-time clock RTC, 2 UARTs, 2 I2Cs, SPI and other bus interfaces, and USB2.0 full-speed interface. It is convenient to expand the USB interface, JTAG debugging interface, touch screen, and has few external expansion chips. In addition, the ultra-small LQFP64 package is used to ensure the miniaturization of the instrument. Moreover, the circuit is relatively simple, which reduces the cost of development and production. The chip can achieve a maximum operating frequency of 60MHz, has strong functions, and can meet the requirements of embedded system μC/OS-II and humanized human-machine interface. All interfaces of LPC2148 are used in this design.

The Ethernet interface uses the ENC28J60 with an integrated MAC and 10 BASE-T PHY with an SPI interface. This greatly reduces the overhead of the main controller's I/O port. The ENC28J60 complies with all IEEE 802.3 specifications and uses a series of packet filtering mechanisms to limit incoming data packets. It also provides an internal DMA module to achieve fast data throughput and hardware-supported IP checksum calculations. Communication with the main controller is achieved through two interrupt pins and SPI, with a data transfer rate of up to 10 Mb/s. Two dedicated pins are used to connect LEDs for network activity status indication.

Figure 2 Ethernet interface circuit diagram

The LED module uses 20 LEDs with 6 wavelengths. The multi-wavelength design makes the measurement more targeted and the measurement data more effective. Our design can measure the brightness of each LED through CCD, and then the LPC2148 controls the size of the current passing through the LED through the point correction function, so that the brightness between the LEDs remains consistent, further improving the accuracy of the measurement. The network chip used in this design is an independent Ethernet controller with an SPI interface, which occupies fewer I/O ports of the MCU.

The CCD module mainly includes the whole machine power supply, CPLD, linear array CCD sensor, operational amplifier and high-precision AD converter.

Software Module Description

The software part of this design is mainly divided into touch screen and LCD module, A/D module, LED control module and network module. This design uses an LCD display with a touch screen, which mainly realizes menu selection, key operation, measured data and status display, which brings great convenience to the operation of this design and allows users to use this product in a relaxed and pleasant environment, which is a highlight of this design.

This design can use an external A/D or the 10-bit A/D converter built into LPC2148. According to the requirements of data accuracy for this design, the A/D built into 2148 is used. This module mainly detects the SH signal generated by the CPLD module. When the signal is high, it processes the detection data and sets the conditions for starting the A/D conversion. When the SH falling edge arrives, the A/D is restarted for the next measurement until the detection is completed. In this module, there is also an important task - data processing. Here, multiple sets of data are collected for each parameter each time, and the average value is calculated. At the same time, it is compared with the standard data to determine whether the parameter is within the normal range, and software recognition of the presence or absence of test paper is added.

The LED control module controls the brightness, display order and display time of LEDs of different wavelengths through a constant current LED driver chip with a dot correction function, so that the optical fiber collects light signals of different parameters and inputs them into the CCD module.

There are two protocols for transmitting data in the network transport layer, the Transmission Control Protocol TCP and the User Datagram Protocol UDP. The TCP protocol is an object-oriented protocol with high reliability, but also high cost; the UDP protocol is a transport layer protocol that provides the least service and cost. UDP is the simplest protocol with the following characteristics: no connection, unreliable, providing application layer protocol identification, improving the checksum of UDP packets, as well as buffering and segmentation. The socket interface function is the API of TCP/IP. When using the socket interface function to write communication tasks, there are two ways: server and client. The server method is to receive data first and then process it, while the client method is to send data first and then wait for response processing. The socket API functions they use are the same.

Conclusion

This is an embedded micro urine analyzer designed for home users. It uses the highly integrated LPC2148 microprocessor from NXP Semiconductors. The USB controller integrated in the chip can be used for power supply and data transmission. The internal ADC can process the analog signal collected by the CCD. The internal SPI interface is used for touch screen and Ethernet communication. The reset part uses NXP's 74HC125.

The instrument diagnoses the health of the human body by detecting 10 components in urine. After the user puts the test strip soaked in urine into the instrument, the LPC2148 controls the multi-wavelength LED to emit light in time, and then the reflected light is irradiated to the CCD through the optical fiber. After signal acquisition and analog-to-digital conversion, and after the normalization algorithm in the LCP2148, the result is output to the LCD for display, or transmitted to the PC as needed.

The innovation of this instrument is that the whole process is operated by a touch screen, which has a friendly human-computer interaction interface. A photoelectric detection system is designed to eliminate the error caused by the mechanical transmission of the traditional urine analyzer and reduce the volume and power consumption. Subsequent work can further study the Ethernet part to realize telemedicine, which is suitable for home users.

Figure 3 Front view of the miniature urine analyzer

Figure 4 Rear view of the miniature urine analyzer

Figure 5 Side view of the miniature urine analyzer

During the design process, we encountered many problems. For example, when adjusting the LCD, the control chip SDE1335 of the purchased LCM used a 5V voltage, while the LPC2148 used a 3.3V power supply. The data interface needed to be connected to a pull-up resistor. At the beginning, we did not find this problem and wasted a lot of time. Later, we connected a 10KW resistor to the data port and the problem was solved. There were also problems with hardware production, insufficient process and funds. When adjusting the touch screen, the button recognition was unstable, etc. Many times, we spent more time and effort, but still could not solve it. I felt that I had reached the end of my rope, but everyone worked hard, encouraged each other, and discussed together, and finally solved them one by one.

Since the system architecture is very large and time is relatively limited, although we have tried our best to develop it, there are still some problems that are difficult to perfect, such as the development of diversified functions of USB communication and greater expansion of Ethernet. We will continue to develop it.

References:

1. Cong Yulong and Ma Junlong, 'Contemporary Urine Analyzer Technology and Clinical Application', Science and Technology Press of China, 1998: 34-57

2. Carlson DA, Statland BE, 'Automated urinalysis[J]', Clin Lab Med 1988,8(3):449-461

3. Zhou Ligong, 'USB 2.0 and OTG Specifications and Development Guide[M]', Beijing University of Aeronautics and Astronautics Press, 2004,9

4. Maejima Takao, Oshigura Taketoshi, Kanda Hiroshi, et al., "Multi-item automatic urine analysis device", Yellow IRIS Overview, SPSMEX JOURNAL 1987, 10, 11