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ZigBee-based wireless surveillance solution infusion

In Electronic Infomation Category: Z | on September 24,2011

in the health care system, patients in the infusion process monitoring problems have been issues of concern to nurses and TEA6425 datasheet and patients, a mistake but will monitor the air into the bodys blood system, resulting in serious consequences even make the patient died. Existing control systems, the use of wired sensor network technology to detect the formation. Such programs are characterized by poor scalability, cumbersome routing, mobility is poor. As a result of the hard-wire connection, the line was easy to aging or corrosion, wear, failure rates are relatively high. Wireless transmission using wireless sensor network built just avoid these problems. In contrast, the wireless way to more flexible, to avoid the trouble of re-wiring, network infrastructure is no longer needed to hide in the wall, move or wireless network can adapt to changing needs; However, wireless communication technology in the field of hospital transfusion monitoring application is relatively small. This is mainly because there is no a wireless communication technology infusion in the hospital for monitoring extensive areas of promotion, and TEA6425 price and existing wireless communication products, high prices, resulting in wireless communication technology applications in the medical monitoring system stagnated. The emergence of ZigBee technology to solve these problems. ZigBee wireless sensor networks and TEA6425 suppliers and automatic control of the combination, can effectively achieve the hospitals infusion control system design. Because ZigBee technology with low power consumption, the system is simple, flexible networking, low cost, latency and other performance, relative to other wireless network technology, it is more suitable for the formation of medical monitoring network, wireless network monitoring.

1 System Design

1.1 bit rate and reserve liquid detection

using infrared photoelectric sensor bit rate. When the droplets drip, the infrared light emitted through the photoelectric sensor intensity changes after the droplets, optical receiver tube receives the optical signal intensity changes in the output voltage signal, this voltage signal is amplified, converted to TTL-after plastic surgery level signal, to send the count to measure the bit rate of the microcontroller. The sensor has a small size, high sensitivity, good linearity and other characteristics, the external circuit is simple, stable and reliable performance.

level measurement using capacitance sensing. Bottle in the reservoir bottle attached two metal facing sheets as sensing capacitors, reservoir level drops, reducing the capacitance between the two poles of the dielectric constant, along with reduced capacitance, through capacitance / voltage converter the output voltage rise. When the reservoir surface down to the warning line, converting the voltage higher than the hysteresis comparator threshold voltage, the comparator output switches turn signal. C / V conversion circuit with excellent linearity, high sensitivity and anti-jamming performance transformation.

1.2 wireless transmission module

logic functions on the node from the network, ZigBee devices can be divided into terminal equipment (enddevice), the routing node (router), network coordinator (PANco-ordinator); from the devices functionality on the distinction between can be divided into full-function device FFD (FullFunctionDevice) and simple functional device RFD (Re-ducedFunctionDevice) [4]. Among them, the full-function device can act as a coordinator of the network, routing node or terminal device, and can only act as a simple function of the terminal equipment device node. Therefore, the logical structure analysis from the network, ZigBee medical monitoring system of the data concentrator is a ZigBee network, the network coordinator; data set point is the routing node; wireless sensor is a terminal node, according to the location of the sensor placement can also be set to routing node. A ZigBee network supports up to 65535 nodes, fully meet the need.

2 system hardware design and operating principle

2.1 data receiver

data receiver use the same wireless transceiver module, and the use of RS232 asynchronous serial communication with a PC. Its function is equivalent to an access point, while the host sends to the data acquisition control signals wirelessly transmitted out on the other hand to receive the data collected and uploaded to the host. System structure shown in Figure 1.

Figure 1 System diagram

2.2 data collection terminal

1) bit rate measurement module

that part of the bit rate measurement using infrared sensors, photoelectric detector model used is the ST-178 infrared transmitter receiver on the tube. Optical receiving device features an internal LED of PI is:

P = Ne * Ni * h * v * I / q,

where: Ne, said outside the quantum effects; Ni said internal quantum effects; I is injected current; q for the flow of electricity over.

the infrared transmitter and receiver tubes are fixed to the front bucket drops on both sides, when the droplets dripping, the infrared light emitted by the transmitter when the receiver drops the signal through the optical power changes, optical receiver tube to change the light signal is converted to electrical signal changes, due to very weak signals should be amplified to a certain extent and to eliminate interference by the integrator, comparator and then through the plastic and drip to get a square wave with frequency. The single-chip pulse counter STC89LE516AD get bit rate. Circuit shown in Figure 2.

2 bit rate measurement test module schematics

2) reservoir liquid level detection module

data collection terminal using capacitive sensors measure the bottle of liquid stock, and the collected data to the wireless transmitter module. Sent by the wireless signal transmitted to the control center module. Schematic shown in Figure 3.

3 reservoir surface detection module diagram

capacitor, the voltage conversion circuit as follows:

input positive half-cycle waveform due to be limiting, the negative half cycle of conduction, the input waveform is a half weeks, limiting the input waveform is 0.7V, the waveform to jump to the 0.7V-E . capacitive voltage characteristic curve of the bottle in the reservoir bottle attached two metal sheets as the sensing capacitor, reservoir fluid level drops, the capacitor between the poles of the dielectric constant decreases, along with reduced capacitance, after the capacitor voltage converter After the output voltage rise. When the reservoir surface down to the warning line, then the measured capacitance value of about 43pF, adjust the hysteresis comparator threshold voltage to below the capacitor voltage converter output voltage, the comparator flip the switch signal output by STC89LE516AD chip wireless transmit module test passed.

3) wireless transmission module

use CC2500ZigBee module, CC2500 is a low-cost, low power, high-performance wireless transceiver chip. The band and the 2.4GHz ISM band; wireless receiver with good sensitivity and strong anti-jamming capability; in sleep mode, only 0.9?? A of current consumption, external interrupt or RTC can wake up the system; in the standby mode of less than 0.6?? A of current consumption, the external interrupt can wake the system; hardware support CS-MA/CA function; voltage (1.8 ~ 3.6) V; in transmission mode, when the output power of-12dBm, the current consumption of 12mA. CC2500 receiver sensitivity of-101dBm (at 10kbps pm); maximum output power of 0dBm, the data rate in (1.2 ~ 500) kbps between the change; with the support of two powerful groups Protocol USART, and 1 one MAC timer, a conventional 16-bit timer and two 8-bit timer.

system works: When the sensor test signal to the liquid stock and bit rate, by the wireless transmission module to send the information to the monitoring center, the monitoring center for computing these data. According to predetermined rules (for example: set the number of liquid stocks for the alarm to alert doctors to perform medical measures), these data into the appropriate police action targets, corresponding to an alarm. Medical monitoring system according to instructions.

3 Software Process

system software by the end of data collection procedures and data receiver components, includes initialization, launch the program and receive program. Initialization program mainly for single-chip, RF chip, SPI, etc. for processing; launch the program will establish a data packet sent by the chip SPI interface module output RF occurred; receiving the data reception process is completed and processed. Receiver software process shown in Figure 4, data collection terminal software process shown in Figure 5.

receiver software flow chart in Figure 4

Figure 5 flow chart of data acquisition client software

4 Debugging and Testing

4.1 debug

1) hardware debug

reservoir liquid level detection circuit debugging. Debugging, the droplets drip, surface water level lower, sensing capacitance value decreases, when the liquid level down to the warning value, the sensing capacitor value by the capacitance / voltage conversion to get the corresponding voltage value, according to the voltage adjustment potentiometer hysteresis comparator to adjust the limits. Bit rate detection and control circuit debugging. Bit speed manual measurement with a stopwatch, and pre-set bit rate comparison, if the error is outside the specified range of experiments with repeated changes in the method parameters set by software algorithms to control the droplet velocity.

2) Software Debug

large software systems, debugging more complex. Required to pass simulator to debug, debugging approach is bottom-up approach, each module is individually tested by, and then connect into a complete system debug, single-chip system successfully downloaded to the tune.

3) soft and hard FBI

link between hardware and software closely, the hardware measurement has been completed, the microcontroller will send data analysis, computing, control.

4.2 index test

1) drip speed test

set by the host and terminal node drops, with two stopwatch timer, a stopwatch used to measure the number of drops per minute and one stopwatch measurement system intended for the drip rate and stable time Table 1.

2) communication system test

using multi-host and terminal half-duplex communication, host-to-end node to complete the monitoring and control functions. Boot, the terminal set terminal number, the host of the terminal to query, if no response within the specified time, then that terminal is closed, shown in Table 2 to Table 5.

test data obtained based on analysis of the system, the setting range (20 to 150) drops / min within the bit rate control, a variety of circumstances the system settling time less than 3s; Meanwhile, the host terminal communication system functioning.

Table 1 drip speed test

2 host control message format

Table 3 host response message format

Table 4 terminal to return the correct response message format

Table 5 terminal returned an error response message format

5 Conclusion

infusion based on the ZigBee wireless technology for medical monitoring system that can accurately capture the infusion bottle liquid stock information, and through wireless transmission to the monitoring system, real-time monitoring of patients. A functional, based on the ZigBee wireless technology, medical monitoring systems will be promoted and applied. With low power consumption and low cost advantage of ZigBees unique system will in the near future to achieve greater development.

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