Megajoy 2 battery limit?

ShaolinDrunkard · Post by **ShaolinDrunkard** » Tue May 03, 2005 10:33 pm

Im entering the final stages of my portable, right now i'm trying to figure out my battery setup. It looks as if my screen will only run of 8 AAs(12v).
At least i mean without modification. My question is, if i hook up my mega joy 2 to the 8AAs will that fry it? It normally takes 4 AAs and has a 9v power supply.

LToidKing · Post by **LToidKing** » Tue May 03, 2005 10:36 pm

I seem to recall the 7805 will take up to 35v and shrink it down to 5v, which is useable by the NES. I'm assuming that Mega Joy 2 runs off the same voltage. Correct me if I'm wrong.

I hope you buy your batteries in bulk!

Dave · Post by **Dave** » Wed May 04, 2005 2:07 pm

From what I recall the mega joy uses some resistors and something else to knock the voltage down to 5v. I don't know how those would hold up to 12v. i would recommend modding the screen for a lower voltage or powering the NOAC through a 7805.

SgtBowhack · Post by **SgtBowhack** » Wed May 04, 2005 5:32 pm

Or you can do the opposite (use 4 AAs and a voltage pull-up to get the screen powered). That'll lower battery life by some, but since the 7805 just burns off voltage as heat, it'd be less wasteful to go up than down (that is, you should get more than half of the power of 8 AAs using the 7805 method with 4 AAs with a pull-up method).

Dave · Post by **Dave** » Wed May 04, 2005 7:04 pm

What would be the best part to pull up power from the 4 AAs?

ShaolinDrunkard · Post by **ShaolinDrunkard** » Wed May 04, 2005 7:16 pm

I looked at my megajoy 2 and it has a 7805 on the board i guess i should be fine then.

Post by **gannon** » Wed May 04, 2005 7:22 pm

Dave wrote:What would be the best part to pull up power from the 4 AAs?

I'd assume a boosting regulator.

nos_slived · Post by **nos_slived** » Wed May 04, 2005 7:23 pm

PT5041

Dave · Post by **Dave** » Wed May 04, 2005 7:28 pm

My superjoy 3 knocks it down with resistors

SgtBowhack · Post by **SgtBowhack** » Wed May 04, 2005 11:36 pm

Yes, what nos_slived said is about what I'd use. Very good efficiency, very low waste of batteries. If I have a chance to make an NESp when I get back, I'll be using that (unless I use a Hip Gear screen that only needs 5v anyway, then I'll just use 4 rechargeable AAs).
Too bad the PT5041 is so expensive

It'd save on space though, and help with things like N64p and stuff where +12v is needed.

Post by **Gamelver** » Thu May 05, 2005 6:58 am

the n64 only needs 7.2v

(along with 3.3v)

SgtBowhack · Post by **SgtBowhack** » Fri May 06, 2005 6:40 am

Errr, right. I didn't mean to say that it did, but they have sister chips for systems like the N64 that need > +5v is all I meant to say.