Video Circuits

Video Activated Relay

This simple circuit from the May 1996 Think Tank column of Popular Electronics activates a relay when it senses a composite video signal. This allows you to use the tuner built into your VCR to turn on and off older TVs that are not equipped with a remote. It can also be used to activate surround sound equipment, turn off the room lights, turn on video game consoles, etc. For such a simple circuit, it is very versatile...

Video Stabilizer circuit

Have you ever attempted to copy a commercially produced video only to end up with a distorted and jumpy image? If so, then you have run afoul of MacroVision. MacroVision is the most popular copy protection scheme used on the majority of content distributed on VHS cassettes. Like all copy protection, it does nothing to discourage the real pirates and only annoys the user who may wish to create a legal copy for backup and archival purposes. This circuit can eliminate MacroVision encoding in both NTSC and PAL recordings...

This is a very basic circuit for fading video signal shown in Eletor Electronics magazine. You can use this between two video equipments. The circuit is so simple that the impedance matching and some other things are not exactly correct, so might not always wor reliably. ..

Video DVM circuit

Video-DVM is a very cheap DVM that shows how an output as complex as a videocomposite signal can be generated entirely in software: two I/O pins and three resistors are all the hardware required. Connected to any TV set it displays voltages, included max and min peaks, using both giant digits and an analog bar-display . A serial data output for computer data logging is provided, too. The micro is the Atmel’s AT90S1200, ideally suited for hobbysts thanks to its 512 words flash memory, public programming protocols, free assembler and simulator available at www.atmel.com. More recently, other tools as free Basic and C compilers appeared on the Internet...

VGA Monitor adaptor for AVR

With commonly available microcontrollers like the Mega8, Mega16 and similar, and with a minimum of external components I wanted a design that would be capable of displaying at least 15x15 characters on a VGA monitor using standard VGA frequencies. The data itself is to be received by the microcontroller via its USART port. All using a 16 Mhz clock for the AVR. The given problem at present is solved successfully. Moreover - the project is a little bit expanded and added by introduction of formation usual Video monochrome (PAL/SECAM) a signal. I.e. depending on position of a jumper type of formed video of signal VGA or Composite Video. ..

LM1881 circuit

This is quite a nice chip, and has myriad uses, but we only need it to perform one function here. Since most game systems output the composite sync information along with the NTSC video output, and since most RGB monitors will not accept this extraneous info along with the sync, we need to remove the video signal. The LM1881 does an admirable job of this. It's a dead easy circuit - one small chip, two small capacitors and a small resistor. As the below pic shows, it's small enough to wedge into a DB-9 hood...

Video Camera switcher MAX454

The video switcher described here can display the output of two, three, or four cameras on a single monitor. The number of cameras is set by a DIP switch on the circuit board. That feature avoids blank displays if less than four cameras are used by sequencing through only the inputs that are connected to a camera. In the automatic mode, the cameras are switched at a rate that can be varied with a panel mounted control. The switching rate can be set from about once per second to about once every 20 seconds. In the manual mode, one camera output is displayed continuously. A momentary-toggle switch is then used to step through the various cameras. The heart of the video switcher is a Maxim MAX454...

video on telephone line wires

The Videowire converts a baseband video signal into a low impedance differential signal that can be sent over ordinary four conductor telephone wire. A send board mounted close to the camera generates the differential signal and a receive board near the monitor converts it back into single wire video that is fed to a monitor. The video signal is sent over two of the four conductors in the telephone wire and power for both the send board and the camera are carried over the other two conductors. The telephone wire connects to the boards with standard RJ11 modular plugs. The send board can be attached to the back of a camera board with pieces of double sided tape or insulated with some electrical tape and tucked anywhere in the camera enclosure. The receive board can be housed in a small metal enclosure. Figure 1 is a block diagram showing power and signal flow. ..

Video title generator

Want to add video to your next project? This device uses a PIC16F819 and not much else. Getting 20 characters to a line is possible by using the SPI port to generate video. Neat trick, eh? The character set is limited to upper case and a few punctuation marks and uses a 'folded data table' to store the image data in the space available. Input to the device is via 9600 baud RS-232 directly from a computer com port. Since this device was designed as a status display, data is placed on the screen by sending a decimal number to designate the screen location followed by up to 20 characters of text and a carriage return. This allows individual portions of the screen to be updated without disturbing the rest of the screen display...

Video Switcher with PIC16F819

This device uses the second method (which, if you don't already know, requires about 100 times less parts), but adds motion detection to switch cameras. The usual way to detect motion is to store a complete video frame and then look for changes on successive frames. Again, a lot of trouble can be saved by only sampling 64 locations on the screen at a low resolution (i.e. just using the A/D in the PIC). Since this device is designed for up to 4 cameras, that is still a lot of data to store in our PIC. Another method was developed to greatly reduce the memory requirements. ..

Audio / Video Distribution Amplifier

With the amount of equipment in home entertainment centers today the need to be able to vary the gain of the audio or video signal is needed. I found this particular circuit helpful when used in conjunction with the Universal Descrambler and a Stabilizer circuit I built for making copies of video tapes. It not only allowed me the ability to fine tune the video strength it also helped me increase the recorded audio which typically becomes poor when making tape copies. Circuit operation is straight forward for amplifier circuits. The second channel for the audio amplifier is made up of the same components except the other half of IC1 is used. Pin 6 & 5 are inputs and 7 is the output...

The GB4551 is a high performance video buffer with DC restore primarily used for accurate back porch clamping. The circuit features a wideband differential amplifier that can be configured as a gain stage. The output signal voltage is limited to +2V above the clamp level in order to prevent damage to crosspoints or other circuits connected to the output...

The HA-5033 is a unity gain monolithic lC designed for any application requiring a fast wideband buffer. A voltage follower by design, this product is optimized for high speed 50W and 75W coaxial cable driver applications common in color video systems. Critical performance characteristics are summarized in Table 1. Outstanding differential phase/gain characteristics combined with an output current capability of ±100mA makes the HA-5033 an excellent choice for the line driver applications required in video circuit design...

A functional block diagram is shown below and illustrates the primary circuit functions. These include equalization, reclocking, and driving 75W co-axial cables. A complete schematic is also included. The EB-RD35 accepts a serial digital data input signal which first goes into the GS9024 equalizer. Equalization of the input signal is completely automatic for signal attenuation due to cable length from 0dB to in excess of 30dB...

The GS4882 and GS4982 are precision sync separators for extracting timing information from NTSC, PAL, and SECAM video signals. The GS4882 generates noise immune and temperature stable composite sync, vertical sync, back porch and odd/even field signals. The GS4982 provides a horizontal sync output for those applications requiring horizontal sync extraction. The GS4882 and GS4982 feature an internal color burst filter for minimization of spurious timing information and the reduction of external component count...