A microphone refers to a microphone used in communication systems, which is generally divided into two categories: universal microphone and anti noise microphone. Universal transmitters are used in general environments and can be divided into active and passive types. Anti noise transmitters are used in environments with high environmental noise, and can be divided into two types based on their working principles: air guided and contact type. The transmitter is one of the important components of a telephone, which can convert sound into speech current, so it is a sound to electricity converter device. Transmitters are generally divided into two types, namely linear transmitters and nonlinear transmitters. People refer to a transmitter whose sensitivity does not vary with the magnitude of sound pressure as a linear transmitter, and vice versa as a nonlinear transmitter. Among the commonly used transmitters, carbon based transmitters are nonlinear transmitters, while electromagnetic transmitters, dynamic coil transmitters, piezoelectric transmitters, and electret transmitters are linear transmitters. There are two types of transmitters: positive and negative. During maintenance, it should be noted that if the polarity is reversed, the transmitter cannot output a signal. In addition, the transmitter also needs to be provided with bias voltage during operation, otherwise, there may be a problem of not being able to deliver the call. The connection methods between the transmitter and the motherboard are touch and solder. The failure of a point-to-point mobile phone to send messages is often due to poor contact between the contacts. It is recommended to clean the contacts first and tighten the shell screws; For soldered mobile phones, the transmitter is soldered onto the motherboard and will not have poor contact. Failure to deliver is often due to dust entering the transmitter blocking the delivery hole or damage to the transmitter itself. Of course, it is not ruled out that the audio circuit may be damaged. There are two types of transmitters: positive and negative. If the polarity is reversed, the transmitter cannot output a signal. The method to determine if the transmitter is damaged is to place the digital multimeter in R × At 1 Ω gear, connect the red lead to the positive pole of the transmitter, and the black lead to the negative pole of the transmitter (as opposed to a pointer multimeter). Speak into the transmitter, and if the transmitter is good, the reading of the multimeter will change or the pointer will swing