The circuit should be powered up before connecting it to an active VGA output, as otherwise the sync signals will feed the circuit via the internal protection diodes of IC1, which can be noticed by a dimly lit LED. LED D1 indicates when the supply is present. Diode D2 provides protection against a reverse polarity. A 78L05 voltage regulator provides a stable 5 V, making it possible to use any type of mains adapter, as long as it supplies at least 9 V. With a monitor connected the current consumption will be in the region of 30 mA. The PCB has been kept as compact as possible, so the circuit can be mounted in a small metal (earthed!) enclosure. This switch should be mounted directly onto the PCB, as any connecting wires will cause a lot of interference. This jumper can be replaced by a small two-way switch, if required. JP1 can then by used to select the correct operating mode. Since the sync in DOS-modes is often inverted compared to the modes commonly used by Windows, the output of IC1a is inverted by IC1b. An EXOR gate from IC1 (74HC86) combines the separate V-sync and H-sync signals into a composite sync signal. To keep the colour balance the same, the resistors for the other two colors (R1 en R3) have to be changed to the same value as R2. In this case the value of R2 should be reduced a little, but this has the side effect that the brightness noticeably decreases and the load on the graphics card increases. It is possible to get synchronisation problems when the display is extremely bright, with a maximum green component. A pull-up resistor on the green output provides a DC offset, while a transistor (a BS170 MOSFET) can switch this output to ground.
These have been added to stop any direct current from entering the VGA card.
The RGB signals from the VGA connector are fed to three BNC connectors via AC-coupling capacitors. The principle of operation is very straightforward. As can be seen, the circuit has been kept very simple, but it still gives a reasonable performance. This circuit has been designed with these types of monitor in mind. There are monitors which only have three BNC inputs and which use composite synchronization (‘sync on green’). Working with us, you will find we are making progress every minute, we are looking for long-term and win-win corporation, and we are selling not only products, but also our idea.There are monitors which only have three BNC inputs and which use composite synchronization (‘sync on green’). We provide the most hearty after-sale services. We offer bulk order with the same high-quality of samples, and we hold the record of ZERO failed part among 5,000pcs. We launch 5 to 10 new products each year.
Our big customers include Sony UK, BENQ Dubai, Shenzhen Metro Group, China Net Com (CNC), Shanda (NASDAQ: SNDA), Foxconn, etc. With strict in-house testing, we can get rid of compatibility problem that most HDMI product could not. With strong R&D Team, we are capable of providing OEM and ODM service all over the world. With more than 300 workers, advanced equipment and completed production line in our factory, we can assure promote delivery of large order and competitive price.
Bnc composite video to vga converter professional#
Lenkeng Technology Limited is a professional developer and manufacturer of all kinds of Audio Video Products.
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