angelo-2.2

Angelo is a low-cost hearing aid designed to selectively amplify voice frequencies.
This is not a medical device and should not be used as such.
It is a simple, yet very functional device that can be easily manufactured and assembled in local communities.
Hearing loss is a condition that is often associated with social stigma and leads to isolation. To solve this situation, the author believes local associations and schools are key to break the initial reluctance of elders to address the issue.
This simple device allows to reconnect with family, TV usage.

Prototype project

This project adds AGC control, pre-amp gain control, reverse polarity protection and revised form-factor in order to fit in a pocket.
This project shall be manufactured by a FabLab in Bergamo, for public events during a local science festival in October 2025.
Device can use an internal microphone capsule or external microphone.
Device requires headset or audio pods for output with maximum sensitivity 97dB and minimum impedance 24 ohms.

Theory of operation

Symmetrical power supply is generated from a 9V battery with TL072 virtual ground circuit with a dual transistor buffer output.
Microphone signal is pre-amplified by TL072 chip which provides band equilization
Volume adjusment is done between pre-amp output and amp input via a potentiometer.
Sound output is generated by LM386 audio chip.
AGC is performed by diode bridge feeding out of phase signal input amp input.