This Oscilloscope Can Read Your Pulse

Taking a pulse is as easy as holding a finger to one's wrist. However, it can be difficult to determine one's pulse accurately without the use of traditional medical equipment. At Makezine, several inventors created a novel pulse reader from an oscilloscope for the task. 

At Makezine, inventors created a basic device that can translate mechanical motion into an electrical signal. The device, designed to read the amount of blood circulation through infrared light, can accurately determine an individual's pulse. However, the device's inventors warn that the oscilloscope pulse reader is not a medical device.

As an individual's heart pumps, blood vessels and arteries in the body contract and expand. For example, a normal blood pressure reading for an individual would be 120 / 80 mmHg. This represents a systolic blood pressure of 120 mmHg and a diastolic blood pressure of 80 mmHg. Systolic blood pressure is reached following the motion of an individual's heart. Diastolic blood pressure is the "resting blood pressure" found in blood vessels and arteries during the times between a heartbeat.

When blood pressure rises, a specialized infrared transmitter / receiver in a finger sleeve receives more reflected light. This causes the detector to pass more current, leading to a voltage drop. Two amplifiers help to filter out noise and emphasize peaks. Both of these systems are integrated into a single chip. An oscilloscope can then read the output.

In its entirety, the device comprises a cable clip, a quad op-amp, resistors, intercom wire, a ceramic capacitor, a 2N3904 transistor, an Arduino Uno, an IR LED emitter / detector and a tantalum capacitor.

If you feel inspired to follow the video and build an oscilloscope pulse-reader, you might consider visiting the page with the YouTube video. A commenter there writes: "Something's wrong [in the video]. Or several things. The schematic doesn't match the wiring 'layout.' The transistor performs no useful function. And the 1st stage should have a feedback resistor too, or it'll eventually saturate."