发布时间 : 星期四 文章中英文翻译更新完毕开始阅读0b4ce803d0d233d4b04e6966
rcumstances, combined with the design requirements of the system and funding considerations, the final choice of the piezoelectric thin-film pulse sensor. The sensor lower prices, and the output voltage change is more obvious, you canachieve the pur
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pose of our experiment.
The piezoelectric thin-film pulse sensor consists of three parts of the silver layer, the piezoelectric ceramic and copper. External pressure is applied to the copper when the piezoelectric ceramic can feel the pressure to produce electrical signals, the signal output and, ultimately, through the silver layer. Use piezoelectric ceramics to be connected through the wires and circuit boards, pay attention to in the welding of piezoelectric ceramic films, can not last long so as not to scorch the silver layer of piezoelectric ceramics.
Piezoelectric ceramics are relatively few data, in order to determine whether to use the sensor to achieve the purpose of the design, the first of its experiment to determine its output voltage to meet the requirements. Only need to the about 4mv-5mv voltage output, you can achieve the design requirements. Piezoelectric ceramics can achieve our targets to be achieved by the test, be able to tell. Following the overall circuit analysis:
The experiment shows, the use of a GaAs infrared light emitting diodes as a light source, the basic suppression caused by respiratory motion drift of the pulse wave curve. Pulse wave detection photoelectric detection technology, so all kinds of interference by stray light around the dark current of pulse amplitude optical modulation technique, in order to overcome the problem of the system. Pulse modulation transmission of sampled values of the modulation signal, as long as the sampling frequency is the Nyquist sampling frequency, you can restore the original signal by a sampling pulse, without causing distortion. The infrared diode frequency of the drive pulse sig
nal selected as the working frequency to an integer multiple of 400Hz to reduce the working frequency interference, the pulse carrier generated by the the ADuC841 internal 16-bit DAC. In order to ensure the stability of the infrared light-emitting diode light source, this article uses the op amp op495 and NPN transistor as a constant current source circuit to the light-emitting diodes to provide a stable working current.
The characteristics of the photodiode is the optical signal is converted to the current and subsequent A/D converter circuit voltage of the detection object.
Therefore, the receiver circuit using current-voltage conversion circuit, the current signal is converted into a voltage signal. Op amp and resistor R form a current-voltage conversion circuit shown in Figure 4-2. S_GND signal, the op amp positive and negative power (5V, 0V to avoid loss of signal, the signal raised to VS_GND = 1V) circuit output voltage.
Photoelectric pulse wave is slowly varying weak physiological signal, the signal to noise ratio low, vulnerable to environmental noise and interference of limb movement. Photoelectric pulse wave signal detection circuit using high-gain amplifier to obtain a higher detection sensitivity, This design ideas led to the detection signal dynamic range reduced by the movement interference will lead to interference signals of the photoelectric saturation distortion of the pulse wave signal detection. The system uses sampling techniques to improve sampling accuracy, high-speed sampling of the signal is equivalent to the signal to analog to digital conversion using high-resolution ADC, to improve the signal to noise ratio and to improve the dynamic range of the effect. Photoelectric conversion signal to analog to digital conversion without the need for any signal conditioning (amplification and filtering) circuit. So-called over-sampling technique is a method for sampling the analog signal frequency is much higher than the Nyquist (the Nyquist) sampling frequency. Quantified by the signal sampling theory shows that the minimum amplitude of the input signal is greater than the quantization le
vel quantizer, and the amplitude of the input signal is randomly distributed, the total power of quantization noise is a constant, 0 ~ fs / 2 frequency range are uniformly distributed. Quantization noise level and the sampling frequency is inversely proportional to increase the sampling frequency, you can reduce the quantization noise level, due to the baseband is fixed, thus reducing the noise power within the baseband, and improved signal to noise ratio improve the resolution and sampling frequency for each increased by 4 times, the signal to noise ratio increased by four times, which is equivalent to the resolution of the A/DC a. Filter for a digital low-pass filter is to filter sampling the high frequency quantization noise outside the signal band, and to maintain the signal within the signal band is essentially the same extract is a sampling of high-speed low-resolution digital signal sampling frequency down to the Nyquist sampling frequency, and then completed the reconstruction of the high-resolution digital signal, anti-aliasing is to filter may reduce the sampling frequency aliasing noise.
Digital filtering and decimation software, flexible configuration. The sensors are infrared emitting diode and the receiving diode measurement principle is as follows: finger on the infrared emitting diode and receiver diodes middle, with the heart beating, finger on the light transmission path, vascular blood saturation level The change will cause the light intensity changes, so the beat of the heart beat corresponds to the infrared receiver diode current change too, which leads to the infrared receiver diode output pulse signal. Pulse signal amplification by F1 ~ the F3 and R3 ~ R5, C1, C2 composed of low-pass amplifier, the amplifier further amplification through F4, R6, R7 and C3, the output signal is sent to F5, the F6, the RP1 After shaping, the R8 and the composition of the Schmitt trigger output, pulse output signal as the MCU external interrupt signal. The variable resistor RP1 is used to adjust the threshold voltage of the Schmitt trigger, thereby adjusting the sensitivity of the circuit.
AT89C2051, X1, R10, C5, and so on up the microcontroller circuit, microcontroller circuit computing results to the digital display, light emitting diodes VD3 pulse measurement status display P3.2 input pulse signal, pulse per beat a light-emitting diodes light time, digital tube DS1 ~ DS3, VT1 ~ the VT3, R12 ~ R21 and such as composition of the digital display circuit. P3.3-the P3.5 port of this machine for three digital control of dynamic scanning driver code output by the transistor drive digital tube, the P1.0-P1.6 port for digital display output of the seven-segment strokes glyph code for drive digital control field.