Microphone signal amplifying circuit

Probe domestic switch needle KG-300K needle head diameter is 3.0mm normally open switch needle

Photocoupler

The following is a circuit diagram of the microphone signal amplifying circuit

Headphone amplifiers (U1, MAX4411) and microphone amplifiers (U2, MAX9812) can be powered directly from a 3V battery. In standard mode, both devices are in shutdown mode, consuming very low battery current. To talk to other people, simply press the transient 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 headphones through resistors R3, 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, R2. Microphones, headphone jacks, transient switches, batteries and other circuits can be mounted in a keychain-sized box with a 1 meter cable and headphone plug.

In the figure, the headphone attenuator/amplifier has a microphone monitoring function to facilitate conversation when wearing headphones.