ad724 circuit
I didn't answer, because I tried all this circuits for myself and after two days of playing I got all clear. First easy part:
@kaeres:
Circuit will work, don't care what service people say. If you have S-video then take this circuit and convert that to Composite video (RCA connector). In this message **broken link removed** lokk at schematic SVHA-RCA.jpg. That is what you need.
@joebazoka, Pharaoh of Egypt:
If you don't have SCART connector then we must modify this circuit, because we can't just "pass" R,G and B signals to composite video like we did at previous schematic. We can feed composite video (RCA) to SCART, but in this case vice versa is not possible. So I tried to solve this and come up with two solutions:
a) Motorola MC1377P (works for color PAL and NTSC)
b) Analog Devices AD722/AD724 (works for color PAL and NTSC)
This is the component list for schematic with MC1377P:
1 DB15P male VGA plug
1 multi-wire cable (I used 8 wires+shield) to connect the VGA to the circuit
box.
1 box (metalic is better, though a plastic one is cheaper, and it's the one
I also used). This holds the circuit. The box is 13cm x 5.5cm x 2.5 cm
(W x D x H).
1 female panel-mountable RCA plug
1 male PCB mountable DC socket
2 male RCA plugs (for the connecting cable)
1 75ê cable, to connect the box to the input equipment. You can probably get
one of these in a shop somewhere. In that case, disregard the 2 male RCAs
above. I used a 50ê cable (by mistake), but it's quite okay. Just don't
use plain audio cable for this. It's AWFUL...
1 12VDC power supply. The circuit I made is only regulated for 5V. The chip
itself (MC1377) has an internal 8.5V regulator. Thus, you can plug in from
about 10V to 14V, unregulated power supply. This means a 9VDC transformer
can be used. I do. The chip needs 60mA maximum, but I haven't determined
the entire circuit supply current needs.
1 Motorola MC1377P chip
1 DIP-20 socket, for the chip
1 7805 5V PS regulator
2 BC547 transistors
1 Philips 330ns delay-line. These are H-A-R-D to find. Motorola suggests a
400ns delay line, though it seems 330ns are more common here in Europe.
Best place to look for one of these things, is inside a TV. The Philips
one is green, and about the size of your thumb (1 inch). I have seen 3 so
far, including the one I have. I have seen 2 other, being used in 2
Elektor Magazine projects. You can try your local TV repair shop. Beware
that some folks don't even know what this is, so be patient...
The impedance on these delay lines is 1Kê. Motorola advises that it falls
between 1Kê and 1.5Kê.
1 chroma bandpass transformer. This one's a little hard to tell what it is.
If you don't know diddley about this, it's one of those things inside the
TV that you turn round and around, which have a lot of wires around them.
About 1 cm high. For details on skiping this, refer to the MC1377P
datasheet. But you can probably get one of your electronics-skilled
friends to built one for you. Here's the details.
The transformer itself is 15mm high, plus 3.5mm for the pins, which are
0.7mm in diameter. Has 2 windings, and each one takes 60 turns of #38 AWG
wire (0.1 m/m).
Unloaded Q (Pins 1-3): 15 @ 2.5Mhz. Inductance: 30æH ñ 10% @ 2.5Mhz.
Bottom view:
___________
/ \
³ 3 -\ /-4 ³ --------
³ / \ ³ ^
³ 2 \ S / S ³ 7 ñ 0.2mm
³ / / ³ v
³ 1 - \- 5 ³ --------
\___________/
1 4.43Mhz crystal, just like the ones found on TVs. 4.43Mhz is the PAL color
carrier frequency. NTSC is 3.58Mhz, so you should get the appropriate one
for you.
Resistors:
1 trimmer, 47Kohm
4 75ohm
3 47ohm
3 1.8Kohm
1 2.7Kohm
1 33Kohm
1 3.3Kohm
2 1Kohm
1 220ohm
Capacitors:
1 trimmer 5pF-25pF (doesn't matter much, get one around this)
1 100uF, 16V (or more V)
1 10uF, 25V
4 100nF
1 12pF
2 1nF
2 10nF
2 180pF
1 33pF (NTSC: 47pF)
1 62pF (NTSC:100pF)
3 22uF
This is datasheet for Analog Devices AD722/AD724 and schematic for RGB to PAL/NTSC composite video.
I will try to send as much as possible data and theory about this project. Because, I have some problems with TV picture on some resolutions, on others not. Some cards (Matrox) are working better than others ...
regards
meax98