Hearing aid circuits consume battery power continuously when it is switched on and this is a serious concern in the design of hearing aid. Researchers recently designed a circuit which saves battery power by means of a sound amplifier section. This circuit is connected with a condenser microphone, earphone and sound detection and amplification sections. For sound detection system, we use a quad op-amp IC LM324 and a timer NE555. The received sound signal near the mic is preamplified by a transistor BC549. It is recommended to use a mono earphone with volume control attached.
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