E L E C T R O N I  S T E T H O S C O P E
It is truly amazing how much data can be collected by a skilled physician using only two basic human senses - touch and hearing. The skill of diagnosing through touch is called "palpation" while the art of listening to patient sounds is called "auscultation". Stethoscope is a device that doctors and sometimes other medical staff use to listen to sounds produced by patient's body. Before its invention, they listened to patient sounds directly by ear.
Stethoscopes through history
The first stethoscope, invented in the early XIX century, looked as tiny wooden trumpet and it both enabled some level of sound amplification via collecting it over a wider area in comparison to putting a bare ear onto a patient skin and also was less displeasing for patients, especially ladies. Over time, the design improved in terms of both comfortability and the level and clarity of sound reproduced. The two most significant improvements in stethoscope design worth mentioning are the addition of flexible rubber tubings, which made stethoscopes not simply much more comfortable but as well much safer for doctors to use, and the improvement in the design of a so called "chestpiece" i.e. a metallic bell used to collect body sounds through patient's skin when pressed onto it. Basic design of this valuable instrument hardly ever changed from mid XIX century until the two last notable enhancements were made in the mid XX century by Rappaport and Sprague and some years later by dr Litmann, both concerning the mechanical and acoustical design of the chestpiece with the aim of providing improved sound clarity and external noise reduction.
As of the first decade of XXI century, the most common type of this valuable instrument is still a purely acoustic one. Despite today's stethoscopes can be in terms of the level of sophistication compared to top quality musical instruments, they cannot overcome the traditional weakness of all passive devices - there is hardly any gain in sound level they provide.
Electronic stethoscopes
As can be expected, all issues mentioned above can be relatively easily overcome using electronics. The most obvious gain of processing signals electronically rather than purely acoustically is - gain. But designing an electronic stethoscope is a bit more difficult than it might seam at first. There are several factors that make this task a bit tricky, such as:
So, making a high quality electronic stethoscope is not a trivial designing task. But if everything works fine, electronic stethoscope becomes a much more powerfull instrument than its acoustic predecessors. Not simply does it enable sound amplification but as well arbitrary filtration, noise reduction, sound recording and reproduction, archieving and sending recordings to consultants via Internet...
The rest of this article describes a working example of a simple audio frequency amplifier suited to fit constraints as described on this page. The circuit provides a notable amplification of weak sounds without introducing perceptable distortions. It can function as a standalone demonstrative device which can introduce doctors to the world of electronic stethoscope sound processing. More skilled hobby designers can consider it a frontend component of a more elaborate sound processing system. Such system can be formed by adding analog or digital equalizer, a more powerful output amplifier, a kind or a recording device such as a PC sound card etc.
designed by LP 2011