As living standards improve, people's growing awareness of health, blood pressure is often health care, early detection of diseases one of the principal means. At present, although there have been several significant electronic device available, but the price is high, relatively large measurement errors, the most accurate or traditional desktop mercury sphygmomanometer, blood pressure table pointer followed. Both blood pressure (Table) accounted for the amount of the current society has more than 90% of patients blood pressure the doctor for the main equipment. Home ownership are also high. However, this requires a stethoscope sphygmomanometer aided measurement of blood pressure, and there should be some measurement techniques, especially for diastolic blood pressure (commonly known as low-voltage) of the judge, the larger human error factors. This paper describes a measurement of electronic aids, for a self-made electronics enthusiasts. The auxiliary measurement device can accurately measure blood pressure becomes easy to not only replace the stethoscope, you can also observe the blood pressure values. Measurement techniques so that people who do not understand can be measured quasi-blood pressure.
How it works:
Circuit shown in Figure 1, collected by sound waves measuring devices, voltage amplification, low pass filtering, wave conversion, voltage detection, sound and light show circuit.
HTD1 the detected pulse wave signal is sent to the gate of V1, in this, V1 impedance transformation from the role. The high resistance of the weak acoustic signal voltage transformation to a low impedance output, the C1, C2, C4 coupled to IC1. IC1 for the quad op amp, its foot internal circuit and external components, the voltage amplifier, adjust the resistance R8 to change the magnification level. The amplified audio signal through R9, C6 coupled to feet inside and outside the low-pass filter circuit, eliminating the human body sensors and external interference signals. And increase the load capacity.feet from the signal output, coupled by C8 to 12, 13, 14 feet for shaping amplification, will transform a square wave pulse wave output from 14 feet. W1 put a lot of adjustment can be changed. 14 feet square wave output signal directly coupled to IC2's feet and 12 feet. Amplified by two operational amplifiers, respectively, and 14 feet from the pin output. feet square wave voltage output coupled to the IC3 by D6 of 12,13 feet. IC3 into four NAND gate circuit, when the 12 and 13 feet is high, pin output low. D7 LED indicator. Adjust the capacity of C12, can change the delay time of the luminous D7. IC2 14-foot high square wave pulse output coupled to the IC3 via the D5 feet, its oscillator circuits inside and outside the foot. pin is high when the oscillator start-up, make noise, the oscillation frequency of about 2000Hz. V2 and IC2's feet from the sound and light circuits simultaneously and so on.
IC1's foot circuits voltage detectors, battery voltage is too low
HTD1 use 27mm piezoelectric ceramics. IC1, IC2 LM324 quad op amp selection. Four CD4011 IC3 and non-selected door, D1 use 4.5V regulator, HTD2 use 15mm piezoelectric ceramic sounder, K use mini toggle switch. Red light-emitting diodes using a micro-D2, D7 highlighted with a mini blue LED, power supply by four AA batteries, and the remaining components as shown.
All components soldered in Figure 2, printed circuit board, into the corresponding plastic box, HTD1 fixed in the appropriate size stainless steel or plastic case, the use of shielded cable and the 3.5mm plug is connected with the measurement, adjust the sensitivity over W1 but do not have high self-oscillation; will take down the battery, switch to adjustable voltage power supply. The voltage to 4.8 V. W2 D1 adjusted so that light can be just.
Schematic of the V1, R1 are encapsulated within the sensor HTD1. It does not draw on the PCB V1, R1 position.
When used, the blood pressure arm band on the arm. Brought down on the arm of the probe HTD1 the brachial artery. When the pressure is estimated that more than systolic blood pressure (commonly known as high-voltage) 2.5 ~ 4kPa (20 ~ 30mmHg) or so, stop the pressure, playing an open valve slowly deflated, systolic blood pressure when the pressure drops, the measurement starts to sound, light direction At this time displayed on the blood pressure is systolic blood pressure, its sound and light are synchronized with the pulse of the beat, sound and light stops shown on the blood pressure is diastolic blood pressure.