With the increase of people’s work pressure, the decrease of exercise and irregular work and rest habits, more and more people are in sub-health state. Coupled with the aging population and other problems, the number of patients with hypertension is increasing year by year. At present, blood pressure has become one of the physical indicators that people pay close attention to.

Electronic sphygmomanometer, with the advantages of easy to use, simple operation and easy to carry, has become one of the effective tools for blood pressure detection. And with the improvement of people’s health awareness, the demand for electronic sphygmomanometer will continue to grow.


Physical drawing of electronic sphygmomanometer

The principle of sphygmomanometer is oscillographic measurement

Oscillographic method, also known as oscillation method, is a method to determine the blood pressure by detecting the vibration generated by the collision of blood flow with the vascular wall, find the pulsatile package trace from the vascular wall, and obtain the blood pressure value according to the relationship between the package trace and arterial blood pressure. What the sphygmomanometer measures is a decreasing pressure curve superimposed with oscillatory pulse signal. The static pressure corresponding to the point with the largest amplitude of pulse wave is the mean arterial pressure. These paired cuff pressure values and the corresponding cuff pressure oscillatory pulse wave are recorded. Through a certain mathematical algorithm, the systolic pressure and diastolic pressure are finally obtained.

The sphygmomanometer scheme based on Jinghua micro sd9315 can directly convert the cuff pressure of 0 ~ 300MMHG into a voltage signal with a span of 31mv, and the constant current excitation source provided by sd9315 can make the measurement signal more accurate.

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Cuff pressure curve


Pulse signal graph

Advantages of sd9315 sphygmomanometer

  • Without an external operational amplifier, the sd9315 chip’s built-in 8bits resistor DAC combined with the built-in OPA amplifier can provide constant current excitation from both ends of the pressure sensor, or select the external reference voltage through the chip ADC to achieve the equivalent constant current circuit effect, which can greatly reduce the temperature drift effect caused by the pressure sensor
  • Built in low-noise high input impedance preamplifier and high-precision ADC can realize the accurate measurement of air pressure signal
  • The chip has two channels of PWM, which can adjust the speed of air discharge and inflation to realize the control of uniform inflation and deflation
  • Four LCD driving modes are supported, including programmable boost module, which can maintain highlight under low voltage conditions. The driving voltage is optional, 2.6V ~ 4.1V, and the step size is 0.1V
  • Built in 1KB user data storage unit
  • With RTC module, can calculate year, month, week, day, hour, minute and second, can automatically calculate leap year

Performance characteristics of sd9315 chip

  • 32 bit MCU (24MHz max), 120K bytes flash, 8K bytes boot, 8K bytes SRAM
  • High precision ADC, ENOB = 18 [email protected] (gain = 256), 4 differential channels or 8 single ended channels
  • Low noise, high input impedance preamplifier, 1,4,8,16,32,64,128 and 256 times gain optional, with offset correction function
  • Built in 12 bit SAR ADC, with self calibration function, sampling time and working mode optional
  • Built in sine wave generator, output frequency: 5KHz, 50KHz, 100kHz, 200kHz, support eight electrode BIA fat measurement
  • Built in two operational amplifiers OPA and OPB
  • Built in high frequency RC oscillator, 24MHz, the accuracy can be achieved after calibration ± 1%
  • Built in low frequency RC oscillator, 32kHz
  • Support high frequency crystal oscillator, 8 ~ 24MHz
  • Support low frequency crystal oscillator, 32.768KHz
  • Typical working current: 400 μ A/ [email protected] , sleep current 3 μ A. RTC is lower than 6 in standby mode μ A
  • Working voltage range: 2.4V ~ 5.5V
  • Working temperature range: – 40 ℃ ~ 85 ℃


Sd9315 function architecture diagram

Schematic diagram of sd9315 sphygmomanometer


Schematic diagram of sd9315 sphygmomanometer

Circuit block diagram of sd9315 sphygmomanometer


Circuit block diagram of sd9315 sphygmomanometer

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