Photo: flickr/Clean Wal-Mart
We love DIY medicine! Doctors who perform surgery on themselves, the use of wooden spoons and champagne corks for medical procedures, smelling old shoes to ward off seizures, and no one can forget the use of Archimedes' principle to measure breast volume! But this paper is even better: it describes how to adapt the electronics from those annoying musical greeting cards to make a very inexpensive pulse sensor. The researchers even taught teachers how to make them and designed experiments to be used for lessons in high school science classes. How cool is that?
Singing greeting card beeper as a finger pulse sensor. "We constructed a robust and low-priced finger pulse sensor from a singing greeting card beeper. The beeper outputs the plethysmographic signal, which is indistinguishable from that of commercial grade sensors. The sensor can be used in school for a number of experiments in human cardiovascular physiology."
Bonus quote and figure from the full text:
"We assumed that a plethysmographic signal from fingers can be detected with a contact microphone firmly attached to a finger. A contact microphone, as such, is not necessarily required since any loudspeaker can, in principle, serve as a microphone... The beepers’ wires were detached from the electronic circuit, and the beepers were removed from the greeting cards. The beepers are housed in a plastic shell on one side, forming an acoustic cavity. The opposite side of the beeper can serve as the surface of a contact microphone... A beeper was secured with Leucoplast adhesive tape to a finger so that the exposed metal side with the soldered wires was in contact with the skin. To stabilize the signal, we constructed a simple passive resistor-capacitor (RC) high-pass filter with a 1-μF capacitor and 100-kΩ resistor soldered to a stripboard, yielding a 1.6-Hz cutoff frequency."
Fig. 1 A: finger pulse (FP) sensor assembled from the beeper and passive resistor-capacitor (RC) high-pass filter. The beeper side contacting the finger is shown oriented upward. A piece of soft rubbery plastic, which originally connected the beeper to the greeting card, was intentionally left on the beeper surface to improve the contact between the finger and sensor. The RC filter's resistor and capacitor terminals are exposed to facilitate the connection of the clips. Inset: scheme of the sensor. The speaker icon represents the beeper. B: the beeper sticked to Leucoplast tape and the forefinger. The tape is glued to the plastic housing. C: the beeper secured to the proximal portion of the last segment of the forefinger.
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