Showing posts with label video. Show all posts
Showing posts with label video. Show all posts
Sunday, September 14, 2014
Video IF circuit TV
The main function of the video IF is to change the 38.0 MHz IF signal into the CVBS signal which later fed into the sound and video to the chroma.
VIF section consists of a series as follows:
IF amplifier
This section serves to strengthen the signal until the signal level is required. IF amplifier is equipped with AGC (Automatic Gain Controller) which controls the strengthening of the IF amplifier so that a constant amplitude output video. Amplifier frequency range from 32 ~ 60 MHz makes this amplifier suitable for applications multistandar.
PLL demodulator and VCO (voltage control oscillator)
IF signal is separated with the help of PLL detector. PLL detector produces a phase reference signal with the IF signal carrier and about 60 KHz bandwidth is determined by PLL loopfilter pin 37. Obtained by comparing the frequency demodulation reference signal with the incoming IF signal. Are required reference frequency (38.0 MHz) generated by the VCO. Appropriate VCO frequency is determined by system calibration using the crystal as a reference. PLL can detect the IF frequency up to ± 1 MHz based on FPLL (Frequency Phase Lock Loop System) which will provide an output signal to the PLL loopfilter for the difference frequency is obtained. If the phase IF signal with a reference signal, the signal is transmitted to the demodulator. Demodulator to control the positive and negative modulation, the selection made by the IIC bus. Low pass filter after the output signal demodulator eliminates the demodulation is not required to process the video.
Video Buffer
Video buffer to produce a video output with an amplitude of the right and keep the video output from the noise peak occurring. The bandwidth of the video buffer at least 6 MHz. In the video there are White spot clamp buffer (for positive modulation) and the noise inverter Clamp (for negative modulation) which keeps the amplitude of the video does not exceed the typical price.
Friday, September 5, 2014
Cell Phone Controlled Audio Video Mute Switch
The schema of the cell phone-controlled audio/video mute switch . This cell-phone-controlled audio/ video mute switch is highly useful in automobiles. The schema automatically disconnects power supply to the audio/video system whenever the mobile handset is lifted off the holder for making or receiving a call. You can use any readily available cell-phone holder with some mi-nor alterations or fabricate it yourself as shown in Fig. 1.
The schema is wired around IC LM555 (IC1), the CMOS version of timer NE555, as shown in Fig. 2. IC1 is used as a medium current line driver with either an inverting or non-inverting output. It can sink (or source) current of up to 50 mA only, so take care while handling it. The audio/video system is connected to the schema via normally opened (N/O) contacts of the relay.
When the cell phone is in its holder, LDR1 does not receive any light from white LED1 and its resistance is high. As a result, the voltage at pin 2 of IC1 re-mains high to provide a low output at pin 3. The low output of IC1 activates relay RL1 and the audio/video system gets power supply via its N/O contacts. LED3 glows to indicate that the audio/video system is ‘on.’ When the handset is taken off the holder, light rays from LED1 fall on LDR1 and its resistance decreases. As a result, the voltage at pin 2 of IC1 de-creases to provide a high output at its pin 3. The high output of IC1 deactivates relay RL1 and the audio/video system does not get power supply. LED2 glows to indicate that the audio/video system is ‘off.’ Preset VR1 is used to control the sensitivity of the schema. Zener diode ZD1 is used for protecting white LED1 from the higher voltage. The schema works off a 12V car battery. Switch S1 can be used to manually switch on/off the audio/video system.
Author : T.K. Hareendran - Copyright: Electronics For You
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