Circuit composed of MAX9812 + MAX4411 to amplify microphone input signal

Figure 1. The headphone attenuator / amplifier has a microphone monitoring function to facilitate conversations when wearing headphones.

Headphone amplifier (U1, MAX4411) and microphone amplifier (U2, MAX9812) can be directly powered by 3V battery. In standard mode, both devices are in shutdown mode, consuming extremely low battery current. When you need to talk to other people, just press the momentary switch SW1 to turn on the microphone. This will turn on the bias output of the microphone amplifier and amplify the external sound signal. Connect the amplified signal to the headphone amplifier and inject it into the audio signal of the headphone through resistors R3 and R4. Another benefit provided by this mixing method is that the low output impedance of the headphone amplifier (when turned on) can further attenuate the audio stream of the original headphone channel.

The sensitivity of the monitoring circuit can be adjusted by changing R3 and R4. The attenuation of the audio input can be adjusted by R1 and R2. Microphones, headphone jacks, transient switches, batteries and other circuits can be installed in a keychain-sized box with a 1 meter long cable and headphone plug.

The Touch Screen Monitor allows the user to operate the host computer simply by touching the icon or text on the computer display screen with his finger, thus getting rid of keyboard and mouse operations and making the human-computer interaction more straightforward. Mainly used in information inquiry in public halls, leading offices, electronic games, song and order, multimedia teaching, air ticket / train ticket pre-sale, etc. The products are mainly divided into three types: capacitive touch screen, resistive touch screen and surface acoustic wave touch screen.

Touch Screen Monitor

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