HEARTBEAT RATE SENSOR USING MICROCONTROLLER
- 2. This project describe a technique to measure the heartbeat rate by sensing the change in blood volume in a finger artery while the heart is pumping the blood. The reflected signal is detected by a LDR(light dependent resistor) sensor. The changing blood volume with heartbeat results in a train of pulses at the output of the LDR, the magnitude of which is too small to be detected directly by a microcontroller.
- 5. The signal conditioning circuit consists of two identical active low pass filters with a cut-off frequency of about 2.5 Hz. This means the maximum measurable heart rate is about 150 bpm. The operational amplifier IC used in this circuit is LM358, a dual OpAmp chip from Microchip. It operates at a single power supply and provides rail-to- rail output swing. The filtering is necessary to block any higher frequency noises present in the signal. The gain of each filter stage is set to 101, giving the total amplification of about 10000.
- 6. A 1 µF capacitor at the input of each stage is required to block the dc component in the signal. The equations for calculating gain and cut-off frequency of the active low pass filter are shown in the circuit diagram. The two stage amplifier/filter provides sufficient gain to boost the weak signal coming from the photo sensor unit and convert it into a pulse. An LED connected at the output blinks every time a heart beat is detected. The output from the signal conditioner goes to the T0CKI input of PIC16F628A.
- 8. The control and display part of the circuit is shown below. The display unit comprises of a 3-digit, common anode, seven segment module that is driven using multiplexing technique. The segments a-g are driven through PORTB pins RB0-RB6, respectively. The unit’s, ten’s and hundred’s digits are multiplexed with RA2, RA1, and RA0 port pins. A tact switch input is connected to RB7 pin. This is to start the heart rate measurement.
- 9. Once the start button is pressed, the microcontroller activates the IR transmission in the sensor unit for 15 sec. During this interval, the number of pulses arriving at the T0CKI input is counted. The actual heart rate would be 4 times the count value, and the resolution of measurement would be 4. We can see the IR transmission is controlled through RA3 pin of PIC16F628A. The microcontroller runs at 4.0 MHz using an external crystal.
- 10. MicroC PRO for PIC- This software used for simulation of code and convert into hex file for the PIC16 Microcontroller. Super PRO - This software used for burned hex file in the PIC16 Microcontroller .
- 11. Heart rate monitor can be used in hospitals for the diagnostic purposes. Since the instrument is not expensive , it can even be used at home. The instrument also has the flexibility which helps us to affix it to vehicles , etc.. The instrument can also be integrated with higher level equipment and used in various applications.
- 12. THANK YOU