other ways to get 3.3v

daguuy · Post by **daguuy** » Thu Sep 22, 2005 8:47 pm

i already asked something about using a resistor to get 3.3v but people said a resistor would die. before i buy anything (i hate buying stuff), i want to see if i can get 3.3v with what i already have. my old joystick broke so i got some big 100k ohm pots out of it and my big multi-use monitor broke so i got a butt load of fairly big and small pots from that. is there a way i could use pots to change 8.4v into 3.3v at 1.3-1.5 amps? what resistance should i use? also, if i get a 3v DC-DC converter from a car adapter, would there be a way to change it to 3.3v by using a pot to connect input to output or would that not work?

usbcd36 · Post by **usbcd36** » Fri Sep 23, 2005 5:51 pm

If you have an older board, it can probably accept 4v or so without any problem, but you could always buy the regulator and tantalum caps from digikey and use a DC-DC convertor to lower it to 5v, then 3.3v with the regulator.

daguuy · Post by **daguuy** » Fri Sep 23, 2005 6:21 pm

what i'm gonna do if i can't use a pot is get a DC-DC convertor. i want to know if a pot would work

Post by **bicostp** » Fri Sep 23, 2005 6:46 pm

Well I'm sure you could use a potentiometer, it would just need some tweaking and you'd hae to lock it with threadlock (the blue/red/green stuff you put on screws to keep the bolts from coming off) so it won't move.

If you don't mind some extra batteries, you could use 3 1.2v rechargeable batteries, which would give you 3.4v...

Math edited. Sorry about that, it's just hard to think straight with bad sinus pressure and a head cold, you know?

daguuy · Post by **daguuy** » Fri Sep 23, 2005 6:51 pm

3, not 2. i'm using one 8.4v battery, not AAs. anyway, thanks for answering my question

superdeformed · Post by **superdeformed** » Fri Sep 23, 2005 8:19 pm

If a resistor wouldn't work, then why would a potentiometer? It's just a variable resistor. Anyways, I doubt that the potentiometers you have are rated for the amount of power that would be going through them if you dropped 8.4v to 3.3v at about an amp of current. You can, however, get a resistor big enough to handle it. Assuming that the current draw actually was one amp, then you would need a 5 ohm resistor (actually 5.1, but lets say 5 to make it more simple), which would drop the voltage from 8.4 to 3.4v. The resistor would also have to be large enough to handle 5 watts of power.

With all of that said, despite the fact that a resistor probably would work, it is definetly not the best way to go. Different games require different amounts of power, which means the 3.3v line is not always drawing a specific current (this is why the power adapter is able to supply so much current to the nintendo). Quite a few people have said that they found the usual draw to be 800mA on the 3.3v line. If you were to use a resistor to achieve 3.3v, you would ideally want 6.375 ohms of resistance, capable of supporting 4.08 watts of power. This set up would work fine for any game that drew 800mA on the 3.3v line, but if it were to draw slightly more, say 900mA, then you would only be getting 2.6 volts, which is cleary not enough.

Considering the amount of time you'll be putting into this project, and also assuming that you'll want it to last and be efficient, you're best bet is to spend the extra $10-20 on the parts to make a proper regulator.

codeman · Post by **codeman** » Sat Sep 24, 2005 5:30 pm

superdeformed wrote: you're best bet is to spend the extra $10-20 on the parts to make a proper regulator.

a regulator is always the best way to go. If you ever need to reduce voltage though, and the current won't always be constant, it can still be done with resistors. You would still need to make sure that the parts you you choose have the proper wattage rating... but if you look up "voltage divider" on google, it'll show you a resistor configuration that will cut the voltage according to the ratio of the resistors.

Mike · Post by **Mike** » Tue Sep 27, 2005 6:39 pm

Hey,
Judging by the age of this topic, you've probably already solved your problem, but I thought I'd mention something about using car adapters. I'm planning on using a car adapter on mine, and if you've got one or can find one, go ahead and slap a voltmeter on it and see what it's really putting out. I've got a 3v sony walkman one for my old minidisc player, but according to my voltmeter it's juicing out 3.4. My only concern is that it says it's rated for 1000mA (one amp) and the N64 says it wants 3.3v at 2.7 amps. There's a one amp fuse on the twelve volt input in the car adapter... do you think it'll manage to power the 3.3v on the N64? I mean, if it doesn't, there's no harm it'll fry it, right? Just not turn on? Has anyone actually used a car adapter in their system before?

Edit: Well, just read another thread and it looks like this has been discussed before, and rather recently. My B.

daguuy · Post by **daguuy** » Tue Sep 27, 2005 7:10 pm

saw a pic somewhere of someone powering it with 2 car adapters in parrallel. now i have a question: if car adapters really do output 3v, would there be a way to put a pot bridging "in" and "out" to raise the voltage a little?

Mike · Post by **Mike** » Sun Oct 02, 2005 4:33 pm

My car adapter puts out 3.4 volts - close enough to 3.3. Anyways, I just tried powering up my N64 on batteries for the first time, running Ocarina of Time. I used one car adapter, and I used a 9.6v racecar battery, 1000mAh. Anyways, it'd power the N64 through the spinny logo thing, and as soon as that was done it would always reboot. My only guess is that the power requirements are met so long as the processor isn't working so hard. Just wondering if anyone else had any keen insight into that. Tempted to run a less strenuous game to see if it has any effect on it. I'd heard that the 12v line doesn't really need 12v... is that wrong? Because that's my best bet, is that underpowering the 12v line is the source of my problems. I haven't fried anything yet though, so that's happy.

Turbo Tax 1.0 · Post by **Turbo Tax 1.0** » Sun Oct 02, 2005 4:38 pm

Mike wrote:My car adapter puts out 3.4 volts - close enough to 3.3. Anyways, I just tried powering up my N64 on batteries for the first time, running Ocarina of Time. I used one car adapter, and I used a 9.6v racecar battery, 1000mAh. Anyways, it'd power the N64 through the spinny logo thing, and as soon as that was done it would always reboot. My only guess is that the power requirements are met so long as the processor isn't working so hard. Just wondering if anyone else had any keen insight into that. Tempted to run a less strenuous game to see if it has any effect on it. I'd heard that the 12v line doesn't really need 12v... is that wrong? Because that's my best bet, is that underpowering the 12v line is the source of my problems. I haven't fried anything yet though, so that's happy.

try charging the battery again

Post by **marshallh** » Sun Oct 02, 2005 4:50 pm

Your car adapter probably puts out 3.1v under load liek mine does.. Didn't you measure the voltage without the n64 connected?
Anyway, the only thing the 12v line is used for is a 7805 regulator, which runs on 7.2-30v or so (varies) and you don't ned much amperage at all on that line. You DO need some capacity on the 3.3v line (at LEAST 1.5 amps, maybe more.)

daguuy · Post by **daguuy** » Sun Oct 02, 2005 5:09 pm

the 12v line can take around 7.2v and very little ma. i've heard the 3.3v line takes around 1.3 amps

superdeformed · Post by **superdeformed** » Sun Oct 02, 2005 5:46 pm

daguuy wrote:the 12v line can take around 7.2v and very little ma. i've heard the 3.3v line takes around 1.3 amps

Last I checked the 3.3v line draws around 800mA (and if it draws 1.3 amps, someone explain to me how both of my portable N64s draw 1.1 to 1.2 amps total off the battery

). I've been checking it with the jumper pack though, maybe it draws more if you use the expansion pack. Also, if you're using a converter or regulator to power it, the draw from the power supply might be a bit higher depending on how efficient it is.

Mike · Post by **Mike** » Sun Oct 02, 2005 7:12 pm

My bet is that it's the car adapter not giving enough current. I tried powering it off of my gamecube power supply (which also gives 12v) and it didn't work either. The light goes on though. This leads me to believe it's not that the power supply isn't capable of putting out enough amps (if the gamecube power supply can power the system and a screen, it should be able to power the N64 no problem). The car adapter does say it's capable of just an amp, I believe, so I'm pretty sure that's the root of the problem. I do have the whole thing in parallell with a half-amp fuse which hasn't blown yet - this means that the entire setup isn't drawing more than half an amp. Wonky. Anyways, it's not fried, because it still works with the wall adapter.