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Friday, December 24, 2010


Measurement of physiological parameters like heart rate and respiration rate is crucial in the field of medicine. Advances in technology have provided different instruments for constantly monitoring these parameters. Here is a simple method for respiration rate measurement using a displacement transducer. This mater can also be used to monitor the to measure the pulse rate and heart rate ( by using a proper sensor).

It uses displacement transducer for sensing the respiration rate using IR transmitter and receiver. Inhaling and exhaling the air during respiration leads to movement of a light weight ball made of (thermocol) up and down in a capillary glass tube. This movement is sensed with the help of IR transmitter- receiver sensor assembly sensing circuit. The

sensing circuit switches on the pulse generator which generates pulses. Thus in this way the movement sensed is converted into pulses. Therefore the total number

of pulses generated in one minute is equal to the number of movements sensed by the sensing circuit. The start switch mentioned in the block diagram is used to reset the display to zero and enable the counter for a minute to count the respiration pulse. The gate pulse generator consists of a monostable multivibrtor when triggered by the start switch; it generates gating pulse of one minute duration. When the monostable output goes high the latch enable of the counter goes LOW and the counted advances. When the monostable output goes LOW the latch enable of the counter goes high and the counting stops. So there is no further change in the count. The outputs of the counter are fed to the input the

seven segment decoder whose output is connected to the input of seven segment display. The segment data and the display enabled pulse for display should be refreshed more than 25 times per second. Thus the display appears to be continuous even though they are not so.

The circuit requires D.C. power supply. Thus to provide that the available AC mains is stepped down by a transformer to deliver the secondary output of 9 volt. The transformer output is rectified by a full wave bridge rectifier and filtered by a capacitor to bypass the ripples.

For accuracy the ball position is required to be adjusted depending upon the age group of the on subject whose respiration rate is to be measured. For instance the displacement of the ball is less for the children, for a healthy person the displacement of the ball is more. In short, the ball should be fixed approximately at the centre of displacement for effective measurement.

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