nesdev.org

http://www.retrousb.com/product_info.ph ... ucts_id=42

I've bought some of these.

Now I was going to try to make something with them. I've bought some eproms that will work with the boards. (27C020 DIP eproms and 27C256)

But I think I am missing one little tiny thing, or two of them.

"Add two 0.1uF capacitors" does the manual say:
http://www.retrousb.com/downloads/repropakmanual.pdf

Hmm, the manual says that this should be added on all variants. But hmmm. My Battle Kid board doesn't have any of them.



So the question is. Do I really need to add them?

If I do, could someone please tell me if these are the one I should buy?
http://cgi.ebay.com/100-x-0-1uF-50V-Cer ... 4aa6c5285c

Wow, there isn't a single capacitor on the board? I guess there's no surface-mount one on the back? Every cart I've seen at least hast a 'bulk' capacitor, usually electrolytic 4.7uF-10uF on the power input. The rule of thumb is a .1uF cap per IC, but it may be overkill to put them all on. Of course I'm sure you've noticed those things can cost less than a penny each, so it's not like it's expensive kind of overkill, heheh.

No, you don't really need it - if it's working on your NES. It's probably OK in general, but I would want them on there if I was going to use it on different systems or trade/sell it and wanted to be sure. And yeah, the caps you linked to would be fine.

I know Codemasters at least seemed to have put carts out that didn't have any bypass caps. But I've also heard of one case where one of their games (Fantastic Adventures of Dizzy) was crashing during the intro, but was perfectly fine after bypass caps were added. But even that cart I'm sure still had a bulk capacitor.

This might be a little odd to ask, but why are capacitors needed on the cart?

Without caps, the power supply might become instable and chips may suddently not behave like they are supposed to due to voltage drops. I've heard that this actually happens.

One every two chips is a good consensus I think. It's not a problem to solder one on the board, but it's a problem to find room for them when designing the board.

Bregalad wrote:Without caps, the power supply might become instable and chips may suddently not behave like they are supposed to due to voltage drops. I've heard that this actually happens.

Oh! As a power stabilizer? I never thought of that, I just always assumed the DC current of the NES was constant, i.e. the built in power supply handled that stuff already. I guess that's a bad assumption, huh?

Hmmm, I wonder why they didn't include these caps on my Battle Kid cart...

In this use they're also known as decoupling capacitors. It solves the problem of having noise in the power supply. The so-called noise is the state changing inside all the various ICs. With larger ICs having hundreds of pins, there will be dozens of bypass caps all around the part. So I was wrong when I said one per IC, it's one for every VCC pin on the IC. Clearly it's not critical on an NES cart, in the same way it is it is on a faster CPU, FPGA, or something (look on a PC mainboard, they usually have many tiny caps directly under the CPU socket).

Kreese: Because it appears to work, it'd be a waste to use the caps if they really weren't needed. Small waste, but it would add up. The NES is well-built and should put out some reasonably clean power, but the exact power requirements are application-specific. It's possible that they're all fine, if they were all built like that - I imagine there would be a lot of complaints if the games crashed randomly, or depending on the NES's temperature, and so on.

It might be interesting to run an NES with some bypass caps removed, or smaller sized, to simulate failed caps or ones that are in the low end of their allowed tolerance range.

You can get ceramic caps up to 10uF that are cheap, small, and surface-mount. That's what I'll be using to replace that pesky and huge electrolytic cap. Usually the main power input cap is 4.7uF or 10uF.