Top1 Sensing circuit of sensing system of wearable lower limb assist robot
Circuit principle:The circuit is composed of detection circuit, signal amplification circuit and regulated power supply circuit. The detection circuit is composed of resistance RH, transistor VT and resistors R1 and R2; The signal amplification circuit is composed of A1, RP1, RP2, R3, R4, R6, R5, R8 and VD3; The regulated power supply circuit is composed of VD1, VD2, R7, R9, R10 and R11 to provide 2.5V regulated power supply for the detection circuit. The resistance RH can use silicon resistance because the response time of silicon at 25 ℃ is less than 5S. Two TL431 are used in the circuit. TL431 is a three terminal adjustable shunt reference source with good thermal stability. Its output voltage can be arbitrarily set to any value in the range from 2.5V to 36V with two resistors. The typical dynamic impedance of the device is 0.2 Ω. It can be used to replace zener diode in many applications, such as digital voltmeter, operational amplifier circuit, adjustable voltage power supply, switching power supply and so on.
When the sensor is worn, the RH resistance of the sensor is also different due to different temperatures, and this resistance becomes the base bias resistance of vt. The different bias resistance makes the current of the base stage different, thus changing the collector current of VT and the emitter current of vt. the emitter current flows through R2, converts the emitter current into voltage in R2, and sends the voltage to the in-phase input terminal of A1, which is amplified by A1 and output, and VD3 controls the output voltage to make the output voltage within 5V.
Top2 Preamplifier circuit of wearable human respiratory state monitoring system
Circuit principle:Human respiratory signal has the characteristics of high bioelectric signal impedance, weak signal and low frequency. Therefore, pre amplification in respiratory signal analog measurement circuit is a crucial link in the design of the whole signal amplification circuit, which is related to the working performance of the whole analog acquisition part. High input impedance, low noise and low temperature drift should be considered in the selection of preamplifier. AD620 is a low-power instrument amplifier, which is especially suitable for the preamplifier stage of small signal. The distortion of small signal amplified by AD620 is very small. The preamplifier composed of one stage AD620 can also control the system error within the range required by the system design. The preamplifier circuit is shown in the figure.
Since the peak value of the output signal of the sinusoidal signal generator is about 1V, the voltage drop on the sampling resistance connected in series with the network load is very small, the sampled signal should be amplified. Two stage amplification is used, and AD620 is used for preamplifier stage. AD620 is a low-power instrument amplifier, which is especially suitable for the preamplifier stage of small signal. The distortion of small signal amplified by AD620 is very small. The preamplifier composed of one stage AD620 can also control the system error within the range required by the system design.
Top3 Circuit design of portable heart rate measurement system based on MSP430
The HRV measurement system is similar to the heart rate measurement system of common fitness equipment. There are two common techniques for measuring heart rate: one is based on electrocardiogram (EKG) and the other is based on optical pulse pickup (as in pulse oximeter system). EKG is the most commonly used technology because it can provide reliable performance for the wearer in any case, and it will not be affected no matter what state the user is in (e.g. shaking or resting). This system requires electrodes to be connected to the user’s chest or arm. EKG is easy to develop and can work continuously, mainly because the amplitude of EKG signal is usually 1 mV. With the help of new low-cost electronic devices, the operation of the process has become quite simple. In the current EKG heart rate measuring equipment, the chest strap sports watch is a good example.
A reference design of EKG heart rate measurement system using msp430g2452.
The circuit can be easily extended to perform HRV measurement. Another way to calculate HRV is to measure heart rate using techniques often used with pulse oximeters. It is an optical pulse pickup system based on pulse oximeter technology.
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