Not having a good performance with the preamp module, I went to a store specializing in electronics, looking for a module that detects the sounds. The only module I found for that purpose was ky-038, which is a module that uses an electret microphone to pick up sounds, ranging from 100 Hz to 10 KHz, covering the detection range of the human voice, incorporates itself into an operational comparator amplifier, the LM393. This module works from a voltage of 3.3V and offers an analogous output for the range of 1Vpp.
When connecting and testing with the horn, an improvement in the detection of sounds is perceived, having a less saturated sound and without noise.
When testing with the "bone transducer", it is possible to perceive the sounds, although somewhat weak. The part of this prototype was satisfying, since with simple elements we could perform the corresponding tests, and see that the idea is functional.
For the following tests it would be necessary to make several improvements, which are:
Have a true bone transducer, since the vibrator motor that we used for the tests, was not designed for this purpose.
Better the stage of audio amplification, having an audio amplifier that delivers more output watts and a low energy consumption.
Design a case with 3d printing, in which all the components are put and be more comfortable to use.
To perform the first tests and see if it is possible to transduce bone audio, we used a small vibrating motor from an old cell phone, which will serve as a bone transducer. The audio amplifier used is the well-known LM386, which for its operation requires few external devices, which offers a quarter watt of power when voltage is supplied below 5V. Everything is fed with a small 3.7V lithium battery.
To test the circuit, the audio signal was sent by a cell phone, and using the "bone transducer" it was possible to perceive the sounds, not like you hear on the horn, but you know that bone conduction works.
A capacitive type electret microphone was used to pick up the sound, but for this to work it is necessary to add a preamplification stage.
For this test a simple circuit was made using a transistor, ceramic capacitors and a few resistors. The performance of this preamplifier is not so good, when listening with the horn the sound is perceived saturated and with noise, and it is necessary to approach the microphone so that it detects the sound.
When using the "bone transducer", it is not possible to perceive anything of what the microphone captures. A better preamp circuit is needed, which improves the detection range of the sounds.
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José Luis
