AUDIOMETER

It is a device which is used to perform audiometry tests where it allows to determine the auditory level of the patient in each of their ears. This consists of an integrated XR2206, 7 buttons to select the frequencies you want, three buttons for the selection of the dB of noise, an LCD for the display of the frequency and also the visualization of the three decibels obtained and finally two buttons to select the ear where you want to hear the sound.

When selecting the frequency, decibel and the ear where you want to listen to the sound depending on the frequency chosen, the sound will change sharply or record the decibels will lower or raise the noise intensity of that sound.

Functioning

To build an audiometer, we used a signal generator XR 2206 with the following configuration:

Figure 1,Signal generator configuration

With this configuration, we obtain a sine wave with different frequencies depending the resistors and capacitors values, with the following equation:  , setting the capacitor’s value C=100nf, we obtain the following resistor’s values for each frequency:

Each frequency had a voltage of 112mv, to change the decibels we used an operational amplifier LM358, calculating que out voltage necessary to get 5dB, 10dB and 15dB with the following equation: 
 

Replacing for each dB values:

Vout is the voltage necessary to obtain the audiometer sound in each dB values, for this reason, we amplify each vin to get that Vout using the operational amplifier shown in the following figure:

Figure 2,operational amplifier configuration

With the gain of the operational amplifier we obtain the Vout values with the following equation to calculate the resistor’s values:

Setting R1=1KΩ

Them, in the audiometer designed, is possible choose the ear where do you want to listen the sound with a single switch, choosing the right or left earphone connection, as shown in the next figure:

Figure 3,earphone connection

Figure 4, Audiometer designed

Programming code:

The frequencies selection was shown in an Arduino interface with Arduino, using a 8 position dip switch to select the resistor to each frequency, when the voltage is 0 in each dip switch position, the Arduino recognize the frequency value, like in the following code:

RESULT 

As you can see below the result of the frequencies shown in the oscilloscope with the use of the resistors found the little lag that was obtained in each of these.

frequency of 125Hz

frequency of 250Hz

frequency of 500Hz

frequency of 1kHz

frequency of 2kHz

frequency of 4kHz

frequency of 8kHz