Use VMR6512 to create a high quality wireless audio repeater, Wireless Audio Repeater
Keywords: Building a high quality wireless audio repeater with VMR6512
Use VMR6512 to create high quality wireless audio transponders
Source: http://www.v-module.com
Wireless FM audio transponders can modulate audio signals into high frequency signals, and receive in a certain distance. Wireless audio transponders are largely applied to wireless headphones, car MP3 forwarders, conference broadcasts, buildings and park broadcasts. The simplest wireless audio repeater can be composed only by a triode, as shown in the following figure:
Fig. One single tube audio FM transponder is made of one triode 9018 constituting an oscillator. The audio signal is input from the triode base, and the volatile diode characteristic of B-E is achieved. Although the circuit is simple, the sound quality is very poor, the stability of the oscillation circuit is very bad, the voltage changes, the human or metal can change the oscillation frequency near the antenna, resulting in unstable receiving ends. Moreover, the circuit can only transfer the mono audio, and the user can't listen to high quality stereo music. Complex stereo repeater adopts an integrated circuit, most commonly used to RoHM's Ba1404. The circuit set is integrated with a stereo encoder, which can generate a stereo pilot signal of 19 kHz as audio. If the radio has a stereo decoding function, you can solve the stereo music. The application circuit of the BA1404 is shown below:
Figure II BA1404 application circuit compared to single-tube repeater, BA1404 can not only transmit stereo signals, but also have a significant increase in sound quality, but the separation, frequency sound and other indicators are still not very ideal, and the sound quality of Ba1404 is still available. A considerable gap. Since the internal use of the BA1404 is still an LC oscillator, the stability of the frequency is still not good enough, and it is easy to generate frequently drifting. It is now quite a large number of car audio transponders or wireless headset finished sales. To create a broadcast-wide sound quality, and the frequency and very stable FM wireless repeater, digital audio pretreatment and complex techniques such as frequency synthesis are required. These technologies are usually only used in the radio station due to cost and complexity, and ordinary users are difficult to accept. Is that high stability, Hi-Fi sound quality audio repeater is not worthy of ordinary users? Beijing Ruiyu Fei Technology Co., Ltd. developed wireless audio forwarding module VMR6512 well solved the contradiction between cost and sound quality and frequency stability, so that all people can enjoy the sound quality of the broadcast level at a very low cost. The following figure is an internal block diagram of the VMR6512 wireless audio modulation module. Be
Figure 3 VMR6512 wireless audio transponder block diagram
The VMR6512 wireless audio forwarding module has the following features:
Broadcasting sound quality L
Completely integrated package, no need for any external components to work L
The audio is processed by DSP, providing high quality provided L.
Using frequency synthesis technology, oscillation frequency is highly stable L
Output power is adjustable, up to 115dBUVL
Frequency range 88.0MHz-108.0MHz, low end can be extended to 76.0MHzL according to requirements
Enter analog audio or digital audio L
Have an external UART interface, which can be easily controlled by an external CPU or PC.
Provide frequency setting up / down input to make it easy to use L
This module can be applied to:
Hi-Fi wireless headset L
Car MP3 audio transponder L
Wireless microphone L
Conference Broadcasting System L
Building music play L
Park music play L
Audiovisual entertainment equipment Annex L
Campus Radio Station L
The interior of the VMR6512 is controlled by a CPU. The external processor can communicate with the module via the UART serial port, and set the frequency, transmit power, interface mode, etc. of the module. In addition, the module also provides two pins for UP and DOWN to perform frequency adjustments without external CPUs or control serial ports. The module default upper electrical transmission frequency is 100.0 MHz, the UP or DOWN pin, each gives a low level pulse, and the transmit frequency is raised or reduced by 0.1 MHz. If the low level is continuously kept continuous on these two pins, the emission frequency changes every 0.3 seconds. The audio signal interface can be a normal analog audio input or a digital audio input. The analog audio first converts the audio A / D converter into a digital signal and then enter the DSP for processing. Digital audio provides three interface modes such as commonly used I2S, Left-Justified, and DSP, which can be seamlessly connected to all CODEC or DSP. After the audio signal digitization, the DSP will filter, pre-heavy, pilot generating, and other processing. Since it is handled in the digital domain, it has an advantage that the analog circuit is unprofitable, providing a premise for high-quality quality. The automatic gain control (AGC) function is integrated in the module. When the input audio exceeds a certain threshold, the AGC automatically attenses the audio signal to avoid distortion. When the audio signal is less than a certain threshold, the AGC circuit will enlarge the audio signal to enlarge, thereby ensuring that the receiving end has a proper volume output. After the signal after the DSP processing, the high-frequency modulator is sent to the high frequency modulator for FM modulation. The high frequency signal is generated by frequency synthesis, and the frequency can be adjusted at a step of 10 kHz. The frequency range is continuously adjustable from 88.0 MHz-108MHz. If there is a special need, it can be extended to 76.0-108.0 MHz. The frequency offset of the FM modulation signal can also be accurately adjusted, but the user is usually not recommended to set it yourself. The output FM signal is up to 115 dBUV, and the empty zone transmission distance can be up to 50 meters.
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