DIY RGB -> Component

[FA-MAS]

Hey, I was referred here by segasonicfan for this question.  I'm looking to build an RGB to Component encoder for use in an Arcade Supergun.  I'm using one of his schematics and I have some questions.  I don't really wanna bug him cause It sounds like it's hard for him to respond due to some issues he's having, so I thought I'd post here for help.  Now, I know I could easily buy the Jrok or the Neobitz encoders to do what I want.  But what's the fun in that   I appreciate any help.

So the schematic's below, and here are my questions.

I understand it's recommended  to "branch off" each power line with a .1uf cap as close to each IC, VCC and VEE.  But I don't know where I'd place the .01uf and 100uf caps in this circuit.  Would someone help me draw it out?

What does he mean by "Bypass initial +5 and VEE (-5) outputs using .1uf, .01uf, and 100uf caps."

So I'll have +5 (VCC) and Ground coming from the Arcade Power Supply right?
I'll have -5 (VEE) coming from the ICL7660 right?
Am I correct in thinking these are the initial VCC and VEE outputs?
Where would I put which caps?

[viletim]

I recommend you use the original as a referance and stick to that as closely as possible.

http://elm-chan.org/works/yuv2rgb/report.html
The last link on the page. Note that Q4 is a 'digital' transistor, ie. two resistors and a transistor in the same package. It can be built from discreet parts.

To generate a negative five volt rail you can use an switching buck regulator such as an LM2594N or perhaps an MC34063A connected in an inverting configuration.  A charge pump like the  ICL7660 is not a good choice because they are very noisy and have poor regulation.

To answer you question, for adequate power supply bypassing you should use one 100n cap for each dual opamp IC, located as close as possible to each IC.

[Segasonicfan]

thanks for helping him out viletim.  This schem is the same as the original on that site (which I pointed him to aswell) only simplified a bit, i.e. showing the resistors for the digital transistor .

You are right about the 7660 and since I wrote this years ago I have since used better circuits to produce a regulated -5v.  The MAX889 is my new favorite for this.  It's a nice simple and easy circuit like the 7660 only with a regulated output, better power supply rejection, etc. 

-Segasonicfan

[FA-MAS]

Thanks for the help guys.  I'm not having a problem understanding the schematic.  I'm having a problem with some of the assumed knoledge that I should have, that's not expressley drawn out on the schematic.  Namely the bypassing.  I understand bypassing the power lines for each ic with the .1uf.  But the comments also say "Bypass initial +5 and VEE (-5) outputs using .1uf, .01uf, and 100uf caps."  My question's been, where do those go.

viletim, I also ran across your post here http://nfggames.com/forum2/index.php?topic=3417.0
It led me to believe that I wouldn't actually need the 74HC4053 since I'd be using arcade boards only, seem right?

[viletim]

SSF,
Your digital transistor equivalent isn't right... see the datasheet attached. Also there is no need for pots on the input for 75R video.

FA-MAS,
Connect a couple of 100n caps between +5v and ground then another pair between -5v and ground. Use thick wires to connect power rails.

If you are using arcade boards exclusively you should omit all components in the dotted box, the 75 ohm termination resistors, and the LM1881. Feed the Composite sync into straight to the Q4. On each video input you should add a pot because arcade video levels vary significantly. The best value would be 1k, connected so the load on the arcade board is always 1k and the wiper feeds the +ve input of the opamp.

[FA-MAS]

So I should do like this?



I didn't draw in the 1k pots on the RGB lines though.

[viletim]

FA-MAS ,

Don't place bypass caps in series, put them across the rail always. You don't really need to use 10 of them but I suppose it won't hurt anything...

And ditch the ICL7660! The thing is practicaly a an electrical noise generator.  The best way to get your -5v is to use a stepdown transformer with a 7905 regulator strung off the end. Failing that, a buck-boost (inverting) converter built around a switching regulator IC would do an adequate job but it a bit more complex. The charge pump (capacitor-switch) is your last resort and if you must use one then pick the best you can find. These are typicaly used for data comms and other app's where regulation is not of high importance.

[FA-MAS]

I'll ditch the ICL7660.  If I go with the transformer+7905 route, where do I get the -5v from?  Everything I've read says that a transformer just steps down the voltage, not convert polarity.  Plus the power supply I'm pulling from only provides +12v and +5v.  It looks like the 7905 just converts one negative voltage to another. Which would be good if I could get -12v

[viletim]

FA-MAS,

Ok, lets keep this a simple a possible. Go and find another game console power adapter or similar which outputs between 9 and 12 volts DC. This contains a transformer, bridge rectifier, and filter capacitor. The output of this will be two wires -- one positive, one negative. Connect the positive wire to the circuit ground, the negative wire will be your -12v or whatever. Built a -5 volt regulator circuit as described on the first page of the 7905 datasheet making sure place capacitors on both input and output (else the device will oscillate).

[FA-MAS]

FA-MAS,

Ok, lets keep this a simple a possible. Go and find another game console power adapter or similar which outputs between 9 and 12 volts DC. This contains a transformer, bridge rectifier, and filter capacitor. The output of this will be two wires -- one positive, one negative. Connect the positive wire to the circuit ground, the negative wire will be your -12v or whatever. Built a -5 volt regulator circuit as described on the first page of the 7905 datasheet making sure place capacitors on both input and output (else the device will oscillate).

I can't say this is an option.  Using a second power supply just for the video converter isn't something that'll work for what my end result's needing to be.  I'm making a supergun, that will only recieve power from a tabletop power supply that provides +12v and +5v.  All i needs is to get -5