Heart-Beat Monitor, For Hospital Use, Voltage : 220V

See the heart rate pulses on LED by sensing blood flow through fingertip using the Heart-Beat Monitor. The Heart-Beat Monitor is the answer to questions like, How could anyone expect an ordinary light dependent resistor photo cell to 'see' through a fingertip in  LED Light and detect the change in blood flow as the heart pulsates? The secret is a high gain circuit, based on a dual op amp IC which can be either the low power CA3140. The LDR is connected in series across the 9V battery supply via a 100kOhms resistor (R2) and VR1 the minute signal used by the blood pulsing under the skin is fed to the non-inverting (+) input, pin 3, of IC1a via a 0.1µF capacitor. Pin 3 is biased by a high impedance voltage divider consisting of two 3.3M Ohms resistors. The feedback resistors to pin 2 set the gain to 11 times. The output of IC1a is fed via a 0.47µF capacitor and 220k Ohms resistor to IC2. This is configured as an inverting op amp with a gain of 45 so that the total circuit gain is about 500. The output of IC2 is used to drive an a LED
Note that the unit is designed to use the good quality light dependent resistor (LDR.) Other LDRs may require a change in the value of resistor R1& VR1. A light source such as a high brightness LED is required. All that is needed is a reasonably well-lit room, preferably natural daylight, to produce a healthy emit LED. Only when the hands are very cold does it make it a little more difficult to accurately count the pulses. To check your heart rate, carefully position your thumb or finger over the LDR and count the LED fluctuations for a period of 15 seconds. Then multiply the result by four to obtain your pulse rate. The circuit cannot be used if you are walking or running, etc.