Keywords: MC2831A assembled FM wireless transmitter
FM wireless transmitter assembled with MC2831A
Author: Wang Zemin
This paper recommends a wireless transmitter assembled by a single-chip frequency modulated circuit MC2831A produced by US Motorola. It has the advantages of good sound quality, small distortion, no runoff, radio frequency transmission stability.
The input of this transmitter can be inserted into the electromagnetic microphone and is used to contact each other in the team. You can also play the music program of the audience such as MP3, CD.
It is also forwarded to the TV sound, and the earphone of the FM radio is received, and the night is avoided to disturb others sleep. The 12V cigarette lighter can be powered in the car when used in the car. The AC-DC regulator power supply can be used.
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The MC2831A transmit special integrated circuit has the characteristics of low voltage power supply, low power consumption. The DIP-16 insert package is used here. Its main technical parameters are as follows:
1. Working frequency: 14MHz ~ 60MHz; 2. Working voltage: 3V ~ 8V; 3. Work current: 4mA (vcc = 4V); 4. Microphone Amplifier: The 5 foot lipitors of the IC are 1mV, f = 1.0 kHz, the closed loop gain is 30dB. Its internal block diagram shows the right figure.
In order to make the circuit simple, there is no audio call and voltage detector inside the MC2831A.
The working principle of the circuit is shown below.
The microphone BM or audio signal is enlarged from the integrated circuit inside the integrated circuit, and the high frequency signal is output to 3 foots to the 3 foot to modulate the high frequency signal. The inductance 11 and the crystal BC are connected in series between 1 pin and 16 pins. 11 At the same time, there is a function of expanding the frequency. 14 foot output The audio-modulated carrier frequency signal is enlarged through VT1. At the same time, 1C on the VT1 collector constitutes 4 times resonance and further expands frequently. The output signal is coupled to VT2 by C10 and amplified by C13 to the antenna.
In the circuit, R9, C14, C11, C2, C3, Vd1 functions as a buck, regulated, and filtering. The MC2831A operating voltage is stabilized at 6V.
Component Selection: VD1 Select the voltage regulator of 5V to 6V. The quartz crystal is 22m to 26.9m crystals. The transistor is modified by the crystal to avoid the radio station frequency. The machine is 25M crystal. VT1 is good with 9018, β to take 70 to 100. VT2 optional 3DA18, 3DG12B and other domestic power tubes, β greater than 50. 11 is 5μH to 10μH for color code inductance. 12, 13 can be removed from a 0.8 mm enameled wire in a drill bit of φ6mm.
The antenna seat is available in the Q9 socket for a walk to connect with the car antenna.
The printed circuit board is shown on the right. It is recommended to integrate the integrated circuit socket with a 16-foot integrated circuit socket, which avoids the welding crafts and damage to the integrated circuit, which is also conducive to maintenance!
After checking the power supply, the power supply is turned on, and the pins voltage of the MC2831A is measured with a multimeter, as long as the value in the schedule is similar. Adjusting R6, R8 allows the VT1 collector current to 15 mA, and the VT2 collector current is 40 mA.
Plug in the electromagnetic microphone, connect a 75cm long copper wire to antenna, open the FM radio, frequency adjustment in 100MHz, and the hand-taking the microphone radio speaker should issue "啪". You can also make a homemade a simple field strength. Carefully adjust the launch site to reach the maximum.
When forwarding MP3, you need to make a connection cable.
At close distance, the antenna can be replaced by a computer terminal 50Ω fake load. If you can pick VU paragraph car antenna on the car, you can be satisfied with the car radio within 400m!
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