so many resistors!

daguuy · Post by **daguuy** » Thu Jun 23, 2005 5:04 pm

is "R=1.7 ohm" a 1.7 ohm resistor? if it is, is this diagram correct?

rawls · Post by **rawls** » Thu Jun 23, 2005 5:32 pm

Yes, but remember that this assumes 1 amp current. As the current changes, the voltage will vary some, depending on the zener characteristics. Also, this will not work if the current goes below 1 amp. What you should do is find the smallest current that the 3.3V part of the N64 needs (i.e., try a bunch of games and figure out what the smallest current will be), and then use a resistor to get that current (R=(5-3.3)/Ismall=1.7/Ismall).

If the current needs don't vary much, then this should work ok. However, there are much better, more stable ways of building a voltage source with a zener; the thing is, though, if you are going to add a bunch of additional components, you might as well just use a switching regulator.

daguuy · Post by **daguuy** » Thu Jun 23, 2005 6:06 pm

this is getting very complicated. i've heard some 3v car adapters can work with lees than 12v. what would work with 8.4v?

Post by **Gamelver** » Thu Jun 23, 2005 6:32 pm

most car adapters I've used can work with 7.2v.....

daguuy · Post by **daguuy** » Thu Jun 23, 2005 6:34 pm

great

Post by **Gamelver** » Thu Jun 23, 2005 6:39 pm

I'd advise against using them, though....3v is just barely enough for the 3.3v line, and even then there's some sound and picture distortion.....if at all possible, go with 3.3v instead

rawls · Post by **rawls** » Fri Jun 24, 2005 10:14 am

You are obviously looking for something easy. Why not just use a 3-pin 3.3V regulator? If you search on Digikey you can find a whole bunch of these. For example, the IR120633 (Digikey part # IRU1206-33CD-ND). Here is the data sheet. All you really need to do is add a capacitor to the output pin and there you go. It can accept up to 12V in and can output over 1A. And it is and LDO so if you want you can drive it off of a few batteries if you want. And this thing is only $1.28. You'll need to heatsink it of course, but it isn't to hard to do this with an N64.

daguuy · Post by **daguuy** » Fri Jun 24, 2005 10:22 am

what uf should the cap be?

rawls · Post by **rawls** » Fri Jun 24, 2005 10:26 am

It says in the data sheet it should be at least 2.2 microfarads. Polarized too (search for digikey under electrolytic capacitor). When I say add the capacitor to the output pin, I mean from the output pin to ground. Look at the datasheet, there is a diagram.

daguuy · Post by **daguuy** » Fri Jun 24, 2005 10:33 am

http://www.digikey.com/scripts/DkSearch ... t=30802624
so does "microfarad" mean "uf?" should i choose 2.2uf and what voltage rating and other stuff do i need?

Turbo Tax 1.0 · Post by **Turbo Tax 1.0** » Fri Jun 24, 2005 10:37 am

would part # 296-13484-1-ND work also

rawls · Post by **rawls** » Fri Jun 24, 2005 12:44 pm

# 296-13484-1-ND has a 25ma max current, so for an N64 it wouldn't be good. It is actually not a voltage regulator, but a voltage reference, meaning it shouldn't be used for things like a portable vg system that will have a decent current draw.

Here are a few more, in stock, relatively cheap ones:

497-1222-1-ND (6V input max)

ADP3338AKC3.3R7CT-ND (8V input max)

IRU1010-33CY-ND (7V input max)

LM3940IMP-3.3CT-ND (7V input max)

LT1963AEST-3.3-ND (20V input max)

RC1117S33TCT-ND (7.5V input max)

These took me less than 5 minutes to find. Remember, what we are doing here isn't super specialized, so most anything you might want will probably be available on Digikey in more than one form.

daguuy · Post by **daguuy** » Fri Jun 24, 2005 2:19 pm

excellent...so i could just get an LT1963AEST-3.3-ND and it would work without any caps or any other stuff like that?

rawls · Post by **rawls** » Fri Jun 24, 2005 2:44 pm

Still needs a capacitor. Most regulators will (especialy LDOs and switchers). The LT1963AEST-3.3-ND wants a 10 microfarad one (again electrolytic and they discourage ceramic ones).

To stave off a $5 charge from Digikey you'll need to buy more than just a regulator, so just buy a regulator and a capacitor. If you go with the IR120633 and a capacitor, you'll still be spending less than $5 for the regulator. So buy a few and some leds and maybe some circuit board and maybe you'll be close to $25.

daguuy · Post by **daguuy** » Fri Jun 24, 2005 2:49 pm

in the search filter thing, it doesn't mention "microfarad" so i assume you mean 10 uf?