The fraction of watt amplifier shown can be powered by voltages from 6 to 9 V. It is not recommended 9V battery, since consumption data to reduce its durability. If source is used, the current must be at least 300 mA and filtering should be excellent. The speaker is 8 Ω and the microphone can be a piezoelectric capsule. The circuit can be used in a warning system, electronic concierge, babysitting or intercom. The power is in the range of 300 mW to 500 mW. The capacitor of 10 µF may be changed, determining the circuit gain. We find this application in the book Mechatronics Sourcebook by Newton C. Braga, published in the United States as a suggestion for robot voice.
