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 NXP Semiconductors


  • Analog/Digital Hearing Aid with Bluetooth Compatibility

  • Created: Sep 09, 2014

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Summary

Most old adults experienced hearing problem. It is caused by disease, side effects of medications, noise that reaches threshold of pain in hearing, and sometimes is hereditary. This circuit provides support to people that have hearing impairment. It is capable of receiving analog and digital signals. It also features immunity to noise that it will not turn ON unless a certain threshold of signal is reached.


The design is comprised of LM324 quadruple operational amplifier that operates with the NE555 timer for sound detection. The LM324 is used as a comparator with voltage reference at pin 3 that is also used for the sound threshold level of the circuit. The BC549 NPN general-purpose transistor is used as part of the amplifier section. It is used as a preamplifier of signal received by the microphone that is also used as the sensitivity switch for LM324 and NE555 timer. The base of BC549 triggers when a sound signal is received and the collector develops pulsating dc voltage that is compared to the reference voltage of the comparator. When the voltage exceeds the reference voltage, the output of the comparators goes LOW and the NE555 timer turns ON. The HIGH output of the timer is directly used as the power source of the sound amplifier. The sound signal undergoes unity follower configuration through the pin 5, pin 6, and pin 7 of the comparator that also resolves the impedance mismatch between the microphone and amplifier circuit. The circuit is comprised of BC549, BC548, BC558, resistors, and capacitors further amplifying the sound signal. The amplified sound signal is then fed to a speaker.


The digital side of the design is comprised of HC-05 Bluetooth module that act as transceiver of digital data. The SC18IM700 I2C bus controller with UART interface relates the Bluetooth module to the PCF8591P. The PCF8591P 8-bit A/D and D/A converter translates the digital signal to analog signal for the speaker output.


The design is quite innovative that targets the old adults. It helps the old adults and some people that have hearing impairment acquire the quality of life and enjoy the technologies of the recent generation. It keeps us attached to our love ones and cherishes every moment that we are with them.

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