Heart beat monitor

1 0-0 5V EE July/August 1986 58 33heart beat monitor C1 820n R4 D2 R6 R15 CA3130 4 1 C2 F 10n C3 l 820n 8 IC4 0000 D2...D5 = 1 N4148 R12 JjA The proposed circuit is based on the fact that the degree of translucence of parts of a mammal"s body de- pends, among others, on the flow of blood. Because the blood supply pulsates at the frequency of the heartbeat, this may be monitored in a simple way without the need for an electrical connection between the mammal and the measuring equipment. In the proposed circuit, the flow of blood through a finger is monitored. To obviate errors caused by the pos- ition of the finger, the receiver diode is included in a loop. The positive input (terminal 3) of ICI is held at about 2.5 V. The gain of the device is determined by the ratio R5:13.4. Network R6-D2 ensures that the circuit stabilizes rapidly. The ampli- fied signal is rectified by IC2 . Time constants R8-C4 and R7-C4 are chosen such that the potential at pin 2 of IC2 has a sawtooth shape. ...