The metabolism of oxygen in the body is an important substance that brain metabolic rate high, systemic oxygen consumption accounted for 20 percent of the total.
In cerebrovascular disease and brain trauma patients in the clinical treatment and treatment, if the lack of oxygen to the brain by means of monitoring, it has the potential to cause brain neural function in loss or damage. Therefore, providing a continuous monitoring brain oxygen supply status of equipment, to improve the cardiovascular and cerebral trauma, disease diagnosis and treatment of major importance. In health care and clinical diagnosis, brain oxygen parameter monitoring is indispensable.This article is applied ARM microprocessor developed a communication with network functionality embedded brain oxygen parameter monitoring equipment.
System hardware design
The hardware system consists of cerebral oxygen detection probe pulse driver circuit, filter and amplifier, LPC2210 system and interface circuits.
Produced by LPC2210 PWM pulse width modulation signals, the probe pulse driver circuit amplifier for driving lights glowing probes, and produce periodic optical signal. Probe of photoelectric sensor collection contains brain oxygen information optical signal, the photoelectric conversion generate an electrical signal. Filter amplifier will receive signals for low pass filter and signal amplification. LPC2210 on amplification of the signal for A/D conversion, and digitally processed through interface circuit extended keyboard, LCM graphic LCD display and RS232 serial port and an Ethernet interface for the entire system of control, display, and host computer (PC) of communication and network communication. The system diagram as shown in Figure 1.LPC2210 system and interface circuits
LPC2210 is Philips company based on a 16/32-bit ARM7 core micro-controller.
It has a very low power consumption, on-chip SRAM 16KB, many 32-bit timer, 8-channel 10-bit ADC, PWM output and up to nine external interrupt, ideal for industrial control, medical systems, etc.System power circuit shown in Figure 2.
220V input after B1 single-phase bridge rectifier, followed by three-Terminal regulators devices U1 and U2 regulator, produces + 5V and-5V voltage, to probe circuit and power amplifier LM324. Because LPC2210 microcontrollers to use two sets of power supply, power supply for 3.3V I/O, kernel and on-chip peripherals for power supply, and therefore in 1.8V + 5V followed the use of low-power chip voltage output 3 .3V and .8V, low-power chip U11, U12 adopts SPX1117M3-1.8 and SPX1117M3-3.3, its characteristics as current, output voltage accuracy is high.This system uses a reset circuit, due to ongoing SP708S JTAG debugging nRST and JTAG emulator nTRST can be controlled using the reset, 3-State buffer gate to drive, 74HC125 as shown in Figure 3.
System clock circuit uses external 11.0592MHz Crystal, make more accurate serial baud rate, while at the same time to support the on-chip PLL function LPC2210, R45 by 1M resistance and received a crystal oscillator, system ends up easily. JTAG interface circuit with ARM company standard 20-pin JTAG emulator debugging interface, definition of its signal and the connection circuit LPC2210 as shown in Figure 3. According to the description of application manual LPC2210, RTCK PIN after another 4.7K drop-down resistance, so that the system reset, the JTAG interface LPC2210 internal enabled, so you can direct JTAG emulation and debugging. This system extends 4MbSRAM (IS6ILV25616AL) and 16MbFLASH (SST39VF160). In order to facilitate program debugging and curing, use Bank0 and Bank1 address space, you can skip the line will LPC2210 CS0 and CS1 respectively assigned to SRAM or FLASH. Program debugging, distributed SRAM for Bank0 address; final code intrinsic to FLASH, FLASH is Bank0 address assigned.Because the system is a system, so use 3.3V has a RS232 level translation SP3232E.
SP3232E is 3V power supply RS232 conversion chips, the receiver and sender respectively the P0.0_TxD0 and P0.1_RxD0 LPC2210. This system has 16 keys for menu options, enter the patient's information, and other functions. The system uses an I2C interface keyboard driver IC ZLG7290, ZLG7290 is a powerful keyboard driver IC that can support up to 64 keyboard.This system uses a dot-matrix LCD module interface circuit, can directly with T6963C LCD module connections.
System uses 8-bit bus, LCD module does not have an address bus, show address and displays the data address by DB0-DB7. Module operating voltage is 5V, i/o voltage LPC2210 3.3V, so in the bus on the threaded protective resistor 470. Let graphic LCD module C/D and A1, A1 control module is used to process the data command, and you can use the 16-bit bus LPC2210 way action graphic LCD module (8-bit data is ignored). CE module sheet selected signal from the A22 LPC2210 and external memory Bank3 piece selected CS3 phase "or" after, when the A22 and nCS3 at 0, the module is selected. LCM interface circuit shown in Figure 4.This system has designed an RTL8019AS chip at the core of the Ethernet interface circuit, circuit schematic diagram as shown in Figure 5.
Because LPC2210 is open bus, so the circuit locatedFor 16-bit bus access to the RTL8019AS, data bus D0-D15 and chip SD0 ~ SD15 connection. As a result of the work of the RTL8019AS voltage is 5V, i/o voltage LPC2210 3. 3V, so in the bus on the threaded 470 Ω protection resistors. RTL8019AS work in jumper mode, the base address for 0x300H, SA6 SA7, on the circuit, SA10 ~ SA19 are grounded, SA9 power supply. SA8 connected with the address bus, SA5 and A22 LPC2210 of external storage attached to the selected Bank3 tablets, CS3 is 1 when the SA8, SA5 0, select RTL8019AS. Other pin connection method to reference the application's manual RTL8019AS.
Probe pulse driver
Brain oxygen probes for part of the preamplifier need system provides + 5V and-5V power supply, voltage bulb will need to provide approximately $ 9V, cycle-4s, duty ratio is 1/3 square wave pulse, to achieve 760nm and 850nm two light sources emitting and detecting rotation to the response of background noise.
Square wave pulse can be achieved by LPC2210 PWM, but its output voltage to 3.3V, enough to drive the probe bulb, so using a switch-mode voltage converter MAX1848, it produces a maximum output voltage to 13V, capable of driving small light bulb. Through the bulb of the forward current and adds in the CTRL pin voltage proportional to the P0.9 and LPC2210 P0.8 defined as PWM State, through the software to produce such a square wave pulse, then the CTRL. When loaded in CTRL on the voltage is less than 100mV, MAX1848 will go off mode, so that you can implement a PWM dimming function. Probes and system circuit between a standard 9-pin connector, easy Assembly and disassembly. Amplifier as shown in Figure 6.Filter and amplifier
EEG data acquisition system in General is in with a lot of electric equipment of the environment, through EEG detector lead line and the body's own distributed capacitance, electromagnetic interference especially 50Hz-line interference, it is easy to approach human body.
Low pass filter is a commonly used method of line frequency interference in addition, this approach makes the circuit are simplified, filter cut-off frequency after about 33Hz. Integrated operational amplifier LM324 will filter after the signal amplification, the by LPC2210 P0.28 P0.27 and conducted A/D conversion is a digital signal, as shown in Figure 6. Then according to the law, the use of software Lambert-Beer related operation, get the oxygen in the brain, through the display output parameters, double probe detects two-sided brain function of local oxygen parameter.System software
System software application ADS1.2 integrated development environment for writing and debugging, it is an ARM company launched the arm core microprocessor integrated development tools.
In the C/O μ S-I I operating systems, application of C language source code, use the CodeWarriorIDE ADS1.2 for OS porting, software compilations, connection to generate binary code. Through JTAG debugger and AXD for debugging, finally FLASH curing to the system.Conclusion
This article describes embedded brain oxygen monitor system circuit design, for dual-sided brain oxygen monitoring of parameters, is available through the serial communication mode will monitor the parameters and the patient's information is transferred to the PC for storage and management, you can also use the Ethernet interface to send information to the remote terminal facilitates remote monitoring and Diagnostics.
At home, in the wild or battlefield surveillance in the broader perspective of the utility.
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