Keywords: FM transmit circuit diagram
I will introduce you to your reference for yourself with several wireless headphones used.
The plan is the frequency modulated wireless transmitter made according to Fig. 1, the whole machine includes only 5 mA where the light-emitting diode is only 5 mA, and any of the FM radio can be stably received within 20 meters, and is not affected by wall blocking Impact. Adjusting the transistor emitter resistance improves modulation distortion, adjusting the signal of the fine-tuning capacity to emit the transmitter within 87 to 108 MHz while avoiding the local modulation station and does not interfere with the television program. The signal source is taken out from the audio output hole of the TV or DVD, VCD with a lotus plug. At the beginning, the AM / FM radio listened with ordinary head is listened, and the effect is very good. After the change, the Sony SRF-MH22 head-mounted number is used to store the stereo radio to listen, the use is extremely convenient, the sound quality is greatly improved, no background noise.
The solution cannot listen to the stereo signal, but also creates a FM stereo transmitter with BA1404 according to the "Electronic News". The machine is only 4 mA when using 1.5V power supply, which can be stable within 10 meters. When you have just made it, press the regular line diagram, and the four-squares BA1404 will not work properly. After careful analysis of the line, it is estimated that the 15PF capacitance of its radio frequency oscillation circuit is short-circuited by the 15PF capacitor of the foot of the foot. After the circuit is turned to work, as shown in Figure 2, this is in production It should be noted. The receiver still uses Sony SRF-MH22, and the mono effect is obvious, and the sound quality is also very good. However, there is a significant background noise in the receiving stereo signal (i.e., the receiver stereo *** opens), and it is not known that the transmitter is caused by the 19kHz pilot signal or the receiver ***. At the same time, the stereo signal separation of the machine is not thorough, and the effect is used.
For high quality receiving three-dimensional sound, you have purchased a blue-roofed headset. Analysis, the machine is similar to the IR900 infrared stereo headset structure introduced in this year "Electronic News". The left and right channels of the transmitter use one of the CD4046 to modulate the signal by two infrared diode, the receiver left and right. The channels are received by infrared reception, transistor amplifying, and then decomposed after the patch integrated block A007B is enlarged and pushed, and the headset is 25 mm. Take a trial, its stereo separation is very good, the sound is clear, the sound quality is very good. Insufficient is that the machine is powered by a battery, and the battery is excessive.
After use, if it is mainly based on the receiving mono signal, use the scheme of Figure 1 to fully meet the requirements. If the infrared wireless stereo system is listened, the frequency modulation specificity is not high due to the signal-to-noise ratio. It is best not to use, of course, using two mono frequency modulated transmitters. It is also a good way to transmit the left and right channel signals, and receive two frequency modulated receivers.
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