The small radio station has two microphones, which can realize the recording of stereo programs. If it is matched with an ordinary radio, it can realize the transmission and reception of a set of high-fidelity wireless FM stereo signals. If there are two such small systems, wireless FM stereo intercom function can also be realized.

In addition, the small radio can also be used for the development of wireless audio products such as stereo wireless speakers, wireless microphones, wireless headphones, and notebooks. The completed circuit board of the small radio station is shown in the figure. It can be seen from the figure that the structure of the small radio is simple and compact, which is very suitable for self-made.

Small radio circuit diagram
The following figure shows the system circuit diagram of the small radio station. The power supply is input by (; K2 socket, filtered by C16, C17, C18, C14, C15, and then sent to fC2. The output +5V stabilized power supply is supplied to fC1 for use, and at the same time through 2 of the 6-digit DIP switches (Figure 2 M1 and M2 of K1), which are sent to the microphone amplifier circuit. MIC1 converts the voice signal into an electrical signal, and sends it to the audio amplifier composed of V1, R6, R7, etc. via C3, and the amplified audio signal is adjusted by C5 to RP1 The volume is finally sent to the left channel signal input terminal of IC1 through C6.

MIC2, V2, RP2, C24, etc. form the right channel audio amplifier circuit, which is sent to the right channel signal input terminal of lC2.

D0, D1, D2, D3 (ie 15-18 feet of IC1) are connected to the 4-position switch of K1, which is used to set the radio frequency point. The composite FM stereo carrier signal is output from pin 11 of Lc1, coupled by C36, and sent to a high-frequency amplifier circuit composed of V3, R21, L3, C37, etc., and the amplified signal is sent to antenna ANT1 through C38 for emission. The external audio signal is input from CK1. LED1 is the power indicator. CK2 is an external power input socket, which can be used with a hollow plug. The center of the plug is positive.

Production and debugging
The above picture is the circuit board of the small radio station. You can refer to the installation diagram in the middle diagram when soldering the components. For the specific installation process, refer to the following diagram. After the welding is completed, use the 8-12V DC power adapter to power the system, and you can start debugging. Set M1 and M2 of DIP switch K1 to "ON" to let the microphone work. For the setting of the DO, D1, D2, and D3 bits in K1, refer to the table below to add one turn to the pre-L2 of the frequency point.

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