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VGA to TV Scart(LM7805)

2017-01-18 23:22  
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This article briefly describes the VGA to TV Scart (LM7805). This principle is easy to understand, but also very practical. Depth understanding of circuit elements, can be more effective to grasp this principle. Do you know the circuit, for example, can understand and buy these components: 74LS86, 2N2222, LM7805 .

This is a circuit converter fromVGAin TVSCARTconnection. Basically it is a circuit that accepts the signals from the exit of cardVGA, him it then changes in combinationRGBcomposite sync and it leads to fastenerSCART. The elements of picture from her exit cardVGA,RED,BLUEandGREENare already ready, bring right tendency the 0.the 7 vpp and right resistance of 75W for direct connection with fastenerSCART, for depiction in the TV. What should it changes it is the right combination the horizontal and vertical synchronization signals from theVGAin a complex signal that will be led to the entryVIDEOin pinSCART. This transformation him they undertake electronic elements of circuit.


Figure 1 

That It Functions:

This circuit has been drawn in order to it changes regular signalsVGA, standardRGBand the complex signal of timing. circuit is simple because signalRGBfrom theVGAis ready in standard level 0,7 Vpp and in 75W charge. For the signals of timing exists a circuit that changes the horizontal and vertical in complex. The circuit is simple based on aTTLcompleted with four gatesXOR, two resistances and two capacitors. His choice completedTTLit is reasonable because the signals of timing ofVGAthey are signalsTTL.

The converter of signals of timing is system that regulates the difference of polarity of signals, so complex signal it is always right. CardVGAuses different polarities in the signals of timing in order to it informs the Monitor anymore analysis it uses. This circuit regulates the changes polarity the signals in least from 200 mSec, that are faster and from the time of regulation of common MonitorVGA. The circuit in order to function need stabilized tendency 5V ( /- 5%) and current 120mA.


ConverterVGAin TV is easy in the manufacture to him it is enough exists a relative experience in the manufactures electronic. The circuit can be manufactured on one smallEPOXYboard. Remember only to connect also the completed circuit with the catering of 5V (in the drawing it does not appear). The circuit in order to it rightly functions it needs without fail stabilized tendency consequently it should you use also aREGULATORLM7805.

In the entry the 7805 the tendency should be from 9 until 16V so that it accomplishes us it gives the desirable stabilized tendency of 5V in his exit. Tendency from 9 until 16V we can him take also from our computer or from exterior small power supply’s socket. From the computer we can we take from the following points: from door RS232, from the parallel door , from the PS2 and finally from a gambling chip of catering by his interior computer.

Big attention should be given in him you stick that you will make and in the wiring of circuit, you avoid the chills you stick why the circuit functions in big frequency and sure will be created instabilities in the circuit with result bad quality of picture or even lack timing in the screen of TV. Be careful in order that the soldering is clean and glazing thus you will only be sure that the soldering has become right. For the wiring you are used shielded cables blentaz and ground the thorax of cables in the board’s chassis. Good it is manufacture it is placed in a plastic box and it is placed and a connectorEURO/scart female for placement in chassis.


U1: 74LS86
C1: 22mFy
C2: 2,2 mF
R1, r2: 2k2
R3, r4, r5: 2k2
R6, r7, r9: 47k
R8: 120
T1, t2: 2N2222
Cable of connectionVGAmale 15pin sub D (DE 15)
Output connector 21pinEURO/scart female



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