AD 725 for RGB encoder-- 3 final questions...

AD 725 for RGB encoder-- 3 final questions...

ok I admit it I'm an elecctronics noob.. I have never taken on any project like this before tho I have learned so much...

Here's the rest of what I need to know...

1. On a cylindrical Capacitor, is the end with the black bar the positive or the negative end?

2. Do I need a Hex inverter if I'm going NTSC?

3. How do I wire the crystal?

If anyone helps me with these questinos, you are boss....

1. You can get the data sheet from the Anolog Devices site.
http://www.analog.com/UploadedFiles/Data_Sheets/774020909AD725_0.pdf
The url you posted to the schematic above is all you need. Apart from the oscillator circuit, there are two options.
It is available as a "block" which has supply, ground and osc out otherwise you can use a crystal and hex inverter. Get the block if you can, to simplify things.

2.I used a single common ground with no probs.

3.) is negative, l is positive.

4. It means the capacitor has no polarity (connects either way), the higher values are electrolytic type hence the )l to indicate polarity.

5.Its a crystal oscillator running at 4 times the colour reference oscillator/sub carrier frequency.
NTSC 14.318180 Mhz
PAL 17.734475 Mhz
I found this the only difficult component to source. Ended up with a crystal and hex invertor, the data sheet has details on this.
You can see the oscillator block bottom left on Arakons neat board
http://pirate.sparkhost.com/~arakon/encoder.jpg
And the hex invertor chip below the AD 725 and crystal top left on my birds nest.
http://www.boomspeed.com/ttooddddyy/ad725.JPG


6. Same as 5

It should be noted that if you go for s-video only and dont bother with the composite option you can cut a number of components out, as the luma trap will not be necessary. With the block oscillator and s- vid only its a very simple circuit. The only discrete componentry being a few decoupling caps and 75 ohm impeadance matching resistors.

That was a verry interesting read... do you have the same for jrok ? i wonder if they handle differently interlaced input ^^

just for my own culture, i like sleeping less stupid than i woke up

thanks tody you rock...

Is a "decoupling caps" the same as capacitors.

You wouln't happen to have any extra crystals???

I should have put them in my digikey order... I don't want to pay that $5 fee+ $4 shipping for 2 crystals.

BarfHappy said:

That was a verry interesting read... do you have the same for jrok ? i wonder if they handle differently interlaced input ^^

just for my own culture, i like sleeping less stupid than i woke up

Click to expand...

Not sure what encoder IC the jrok uses, it maybe a Sony CAX chip as used in the AES.

norton9478 said:

You wouln't happen to have any extra crystals???

I should have put them in my digikey order... I don't want to pay that $5 fee+ $4 shipping for 2 crystals.

Click to expand...

I dont have any spares, there isnt much call for 4FSC crystals. Infact I built two identical superguns, one for a friend, and managed to loose one crystal , so Im waiting on another at the moment.

Decoupling is one of the functions of a capacitor, essentially dc blocking.

I'm actually working on a full pcb:
an international video converter for standard res. jamma games.
With the help of both LM1881 and AD725...
You can choose the output format between ntsc and pal.
There is a S-VHS and composite and buffered RGB output.

thanks looks cool...

are you going to go full production with them????

and what is a LM1881???

It's just the begginning, i have to change a little bit the p.c.b.
Yes, if it works perfectly.I can product it.
In fact i'm doing this converter for a friend in Belgium, and they also use your video standard.
The lm will change the synchro signal in a standard signal.
it's a cheap compo. so you can try, it will cost you something like 5$.
Just use good MKT(polyester) capacitors.

http://www.jameco.com/cgi-bin/ncomm...1&prrfnbr=2839&cgrfnbr=708&ctgys=503;521;708;

So can I use this Crystal???

I know it's a lil expensive, but I have to place an order with jameco anyways...

norton9478 said:

http://www.jameco.com/cgi-bin/ncomm...1&prrfnbr=2839&cgrfnbr=708&ctgys=503;521;708;

So can I use this Crystal???

I know it's a lil expensive, but I have to place an order with jameco anyways...

Click to expand...

yes, that will work for ntsc.

posted 3 new questions at top... thanks... you guys rule...

1. The black bar indicates the negative connection on an electrolytic capacitor. (or white bar if the cap body is black)

2. For ntsc or pal you will only need the hex inverter if you choose to use a parallel resonant type of crystal. Like the one used on my project.(its has only two connections) The hex inverter is required to create or drive the oscillation then buffers it before applying to the AD725.(crystals do not oscillate of their own accord.) "TTL Crystal Oscillator
A single component oscillator utilizing a combination of thick film hybrid and quartz crystal technology. Suitable for use in computer and digital based equipment."

If you use this type of oscillator block as used in arakons project you dont need the hex invertor, as the oscillation occurs within the device and fed straight to pin 3 of the AD725. You will notice the device has 3 connections, 5 volt supply, ground and oscillator output.

3. Depends on which method from 2. above you choose.
It shows the wiring on the data sheet.
If your worried about the hex inverter dont use the parallel resonant crystal option, use the oscillator block as on arakons encoder.

Thanks toddy, you rule the electronics world... Ijust wish there was some kind of book or website that explained all this shit... Most books and sites go straight into theory without saying how to actualy hookt he shit up.......

I am using this crystal:
http://www.jameco.com/cgi-bin/ncomm...ys=503;521;708;

Unfortounatly I just lost 4 of them in my house and need to order more......

I belive I don't need a hex cuz it has the 3 prongs (+5, output and ground)...

SO i do put a capacitor between the crystal and the ground? I asume that the oscolator (as shown on the analog schematic) part is already grounded through the crystal...




...thnx

norton9478 said:

Thanks toddy, you rule the electronics world... Ijust wish there was some kind of book or website that explained all this shit... Most books and sites go straight into theory without saying how to actualy hookt he shit up.......

I am using this crystal:
http://www.jameco.com/cgi-bin/ncomm...ys=503;521;708;

Unfortounatly I just lost 4 of them in my house and need to order more......

I belive I don't need a hex cuz it has the 3 prongs (+5, output and ground)...

SO i do put a capacitor between the crystal and the ground? I asume that the oscolator (as shown on the analog schematic) part is already grounded through the crystal...




...thnx

Click to expand...

Connect the 5 volt supply to the +5 volt input of the oscillator.

Connect the the oscillator ground connection to ground (the screening can will also be grounded)

Connect the oscillator output to pin 3 of the AD725.

Connect the 0.1uF capacitor between the +5 volt input to the oscillator and ground (as close as possible) this capacitor does not have a polarity. This capacitor is placed here to filter out noise that may be present at the 5 volt in to the oscillator.

Please forget about hex inverters