1. INTRODUCTION
This test assesses your ability to hear sounds. The sounds vary according to the volume or force (intensity) and the speed of vibration of the sound waves (tone). Hearing occurs when the sound waves stimulate the nerves of the inner ear. The sound then travels along the nerve pathways to the brain.
Audiometry provides a more accurate measurement of hearing. For this test, hearing aids that are connected to the audiometer are used. Pure tones of controlled intensity are generally transmitted to one ear at a time. It is requested to raise your hand, press a button or indicate otherwise when you hear a sound.
List of Equipment and Materials:
• Voltage source (Dual)
• Oscilloscope
• Connectors
•Multimeter
• LCD (16×2)
• Arduino one
• 1 Mega potentiometer
• 50 KΩ potentiometer
• Dip switch with 4 positions
• 8-position dip switch
• 1 Resistance 470 KΩ
• 7 1 KΩ resistors
• 1 10 KΩ resistors
• 2 100 KΩ resistance
• 1 Resistance of 150 KΩ
• 1 LM 358 Operational Amplifier
• The Protoboard
• Protoboard cable
2. CONTEXT
The sound waves can travel to the inner ear through the external auditory canal, the eardrum and the bones of the middle ear (air conduction). They can also pass through the bones that are around and behind the ear (bone conduction).
The INTENSITY of sound is measured in decibels (dB):
A whisper is approximately 20 dB.
The loud music (some concerts) is around 80 to 120 dB.
The engine of a jet is roughly 140 to 180 dB.
Sounds with more than 85 dB can cause hearing loss after a few hours. Stronger sounds can cause immediate pain and loss of hearing can occur in a very short time.
The TONE of sound is measured in cycles per second (cps) or Hertz:
The bass tones of a bass fluctuate between 50 to 60 Hz.
The highest elevation treble tones are approximately 10,000 Hz or more.
The normal range of hearing of humans is approximately 20 to 20,000 Hz. Some animals can hear up to 50,000 Hz. Human language is generally between 500 and 3,000 Hz. [1]
General Objective: Design an audiometer that produces pure tones of several specific frequencies that can be heard through headphones and allow them to be visualized in LCD (16×2) with the help of the arduino to determine the auditory response of a patient.
List of Equipment and Materials:
• Voltage source (Dual)
• Oscilloscope
• Connectors
• Multimeter
• LCD (16×2)
• Arduino one
• 1 Mega potentiometer
• 50 KΩ potentiometer
• Dip switch with 4 positions
• 8-position dip switch
• 1 Resistance 470 KΩ
• 7 1 KΩ resistors
• 1 10 KΩ resistors
• 2 100 KΩ resistance
• 1 Resistance of 150 KΩ
• 1 LM 358 Operational Amplifier
• The Protoboard
• Protoboard cable
Audiometry
It is a test to assess the auditory capacity through the stimulation of the auditory system by means of the use of pure sounds of different tones at the same intensity or of the same tone at different intensities generated by an electronic instrument designed for this purpose. It is used in the population occupationally exposed to noise, as a tool for the early detection of cases of hearing damage, ideally when they are still asymptomatic, as well as to evaluate the effectiveness of the management carried out in the Epidemiological Surveillance Systems or Programs to control this factor. risk in work environments.
Recommendations for the realization of audiometry:
• The worker must have an auditory rest of 8 hours before performing the audiometry.
• The audiometry will not be performed if at the time of the examination the patient presents infectious processes such as pharyngitis, sinusitis, bronchitis, otitis, etc.
• The patient should not have auditory rest for the previous 8 hours (no exposure to work noise, no hearing with headphones) [2]
figure 1. test audiometry
Types of audiometry
The audiometry is carried out evaluating the «airway» and «the bone pathway»:
• The airway: assesses the ability to detect sounds presented / transmitted through the air, specifically through headphones.
• Bone pathway: assesses the ability to detect sounds transmitted through the bones of the head. In this case a vibrator is used that is placed behind the ear.
Operational Amplifier:
An operational amplifier (op-amp), is a general purpose linear device which has signal handling capability from f = 0 Hz up to a frequency defined by the manufacturer; It also has signal limits ranging from the order of nV, to a few dozen volts. Operational amplifiers are characterized by their differential input and a very high gain, generally greater than 100dB.
The A.O is a directly coupled high gain amplifier, which is generally fed with positive and negative sources, which allows it to have excursions both above and below ground.
The ideal Operational Amplifier is characterized by:
• Input resistance, (Ren), tends to infinity.
• Output resistance, (Ro), tends to zero.
• Open loop voltage gain, (A), tends to infinity
• Bandwidth (BW) tends to infinity.
• vo = 0 when v + = v- [3]
XR2206:
XR2206 is an integrated circuit designed by Exar Corporation, which can be used as a generator of signals of sine waves, squares, pulses, triangular and sawtooth, the frequency and wave amplitude can be varied if the voltage is controlled. It can also be used as a voltage to frequency converter, making it suitable for use as a radio frequency transmitter, either FM or AM.
3. DEVELOPMENT
The operational characteristics of the XR2206 and the values of the components used are the following:
• Supply voltage between 10 and 26V.
• Power supply between 12 and 17 mA.
• Operating frequencies between 0.1 Hz and 1 Mhz.
• Temperature stability from 10 to 50 ppm / oC.
• Stability in io amplitude, 5 dB: from 0.5Hz to 1MHz.
• Amplifier output impedance: 6,000.
• Linearity of the triangular serial: better than 1%.
• Distortion of sinusoidal signals: less than 0.4%.
• Maximum amplitude of the triangular signals: 3V.
• Maximum amplitude of the sinusoidal signals: 0.8V.
• Recommended value of the distortion setting: 470 Ω.
• C value: between 1 nF and 100 μF.
• Command levels of the FSK input: 0.8 to 2.4V.
• Input impedance AM: 50 to 100 K. [4]
figure 2
COUPLE
It has also been necessary to perform a coupling of the hearing aids with respect to the circuits since for some frequencies in the square signal to be more specific, the audio signal is not perceptible.
figure 3
4. RESULTS
For the calculation of the beats per minute we must take into account that we must divide it between the display time that we have in the oscilloscope and the number of frames between peak and peak that exists in the signal
5. ANALISYS OF THE RESULTS
For the design of the Audiometer there were different stages. The first stage in the class session was the design of the audiometer as such and understanding the whole theoretical part of the frequency and decibel handling in the patient, the second stage was the assembly of the audiometer without visualization with In order to be able to listen to the hate, either simultaneously or interspersed with the frequency in the third stage, the part of the arduino code was added with the visualization on the LCD with the main objective of observing frequencies and decibels (db) based on the arduino code, but for this code there were too many drawbacks since the frequencies were sometimes not shown properly on the lcd and in the same way it happened with the part of the db, what was done as the next and last stage was analyze the code carefully and try new variables so that the visualization was appropriate and made sense.
Finally, a positive result was obtained when observing different sound frequencies and decibels in the patient, since the code used in the Arduino was the expected one since the visualization was given correctly in the LCD without any anomaly; observing additionally on the screen.
Where the hearing ability of the human being can degenerate due to the different sound variations that occur in the middle. In addition, the human being has the ability to hear sounds with frequencies from 20 to 20,000 Hz.
6. BIBLIOGRAFY
[1]Medlineplus (2017).Audiometría. Recuperado (10 de mayo de 2018) en “https://medlineplus.gov/spanish/ency/article/003341.htm”
[2]Audiología (2017).Audiología Blog . Recuperado (10 de mayo de 2018) en “https://audiologiablog.wordpress.com/tipos-de-perdida-auditiva/”
[3] ¿Qué es un amplificador operacional (2013)? Amplificador. .Recuperado (8 de Marzo de 2018)de:“http://www.pablin.com.ar/electron/cursos/introao1/quees.html
biomedica 