【文章內容簡介】 2. 2 ADC0809 is introduced This system use ADC0809 and pressure sensor of BP01 blood pressure detection section. ADC0809 is 8 bits A/D converter, 8 road multiway switch and microprocessor patible control logic CMOS ponents. It is successive approximation A/D converter, can direct interface with singlechip microputer. ADC0809 internal logical structure Figure 4 ADC0809 internal structure By above knowable, ADC0809 analog switch by an 8 road, an address latch and decoder, an A/D converter and A tristate output latch. Multiway switch optional eight analog channels, allowing 8way analog input, timesharing share A/D converter. Tristate output is used to latch lock A/D convert the digital quantity, when the OE end for high electricity at ordinary times, can from three states the output latch removed after conversion of data. Pin structure Figure 5 figure ADC0809 pin IN0 IN7:8 analog input channels ADC0809 for analog input requirements: signal single polarity and voltage range is 0 to 5 v, if the signal is too small, must be large。 Input analog in the process of transformation should remain the same, if analog changes too fast, need to increase the sampling keeping circuit before input. Address input and control line: 4 ALE to address latch allow input line, the high level effectively. When the ALE line for high electricity at ordinary times, address latch and decoder will be A, B, C three address line address signal is latched, after decoding the selected channel analog transformed into the converter. A, B and C for address input line, used for gating IN0 IN7 analog input all the way. Channel selection table shown in the following table. C B A selected channel 0 0 0 IN0 0 0 1 IN1 1 0 0 IN2 0 1 1 IN3 1 0 0 IN4 1 0 1 IN5 1 1 0 IN6 1 1 1 IN7 ST for conversion start signal. When jumping along the ST, all internal registers reset。 Under the edge, to begin A/D conversion。 During the period of transformation, ST should maintain a low level. EOC as the end signal conversion. When the EOC for high electricity at ordinary times, show that transformation over。 Otherwise, it shows that the ongoing A/D conversion. OE as the output enable signal, is used to control the three output latch to microcontroller output data conversion. OE = 1, the output data by converting。 OE = 0, the output data in high impedance state. D7 D0 for digital output line. For clock CLK input signal lines. Because of ADC0809 internal clock circuit, the clock signal must be provided by the outside world, usually use frequency is 500 KHZ. VREF (+), VREF () as the reference voltage input. ADC0809 use Ⅰ . ADC0809 internal with the output latch. Ⅱ . Initialization, ST and OE signal for low level. Ⅲ . Which send to convert channel of addresses to A, B, C on port. (this design using only the first channel IN0). Ⅳ . At least 100 mu in ST side give a s wide is the pulse signal. Ⅴ . Whether conversion finished, we according to the EOC signal. Ⅵ . When the EOC is a high electricity at ordinary times, then gave OE for high level, and converting data output to the single chip microputer. a heartbeat detection principle design The pulse signal of the heart rate sensor with piezoelectric ceramic (install a sea in the piezoelectric ceramic chip pad to) pulse signals。 Will gather to the heart rate signal is posed of CD4069 3 gate level 3 amplifier circuit of amplification, and then by the level 2 trapezoidal filter circuit, posed of a series resistor capacitor filter processing, can obtain the human heart rate range of signal (approximately between Hz to Hz)。 Through posed of diode detecting circuit, posed of three gate shaping circuit processing, microcontroller are available on the required standard of 0 to 5 v pulse signal. It received a MCU external interrupt of each interrupt a count. Every minute a show the minutes of the heart. the principle of temperature detection and design DS18B20 is introduced: DS18B20 is DALLAS semiconductor panies in the United States after the DS1820 a kind of new advanced intelligent temperature sensor. Compared with the conventional thermistor, temperature and he can read out directly according to the practical requirements through simple programming 9 ~ 12 way of digital reading. Can be done within ms and 750 ms respectively nine and 12 digital quantity, and information from DS18B20 read or written to DS18B20 information need only the mouth thread (single wire interface) to read and write, temperature transform power from the data bus, the bus itself can also supply power to the DS18B20 articulated by without additional power supply. Thus using DS18B20 can make the system more simple structure, higher reliability. He on temperature measurement accuracy, transformation time, transmission distance, resolution of the DS1820 had greatly improved, and gives the user the use of more convenient and more satisfactory effect. DS18B20 adopts 3 feet PR35 encapsulation or 8 feet SOIC package, as shown in figure 6 Figure 6 pins of DS18B20 DS18B20 internal structure is mainly posed of four parts: a 64 bit lithography ROM, temperature sensor, the temperature of the nonvolatile alarm trigger TH and TL, configuration register. ROM in a 64 bit serial number is good before delivery by lithography, it can be seen as the DS18B20 sequence of address code, each DS18B20 64 serial Numbers are not the same. 64 rows of ROM cyclic redundancy check code (CRC = by 8 + x 5 + X4 + 1). ROM role is to make every DS18B20 each are not identical, so it can realize the purpose of a bus to hook up multiple DS18B20. The internal structure of [2] as shown in figure DS18B20 temperature conversion