Bamboori
Offline
Germany

i dont want my saves to perish at any time, so i want to make my cart run on a li-po cell (one of those tiny ones used for rc helicopters and the like).
now the li-po cell outputs 3.7v, so ill have to use a 3v regulator for that. charging ciruit boards are also incredibly small (not much bigger than the four soldering points on them).
i only have to figure out two more things:
-how do i charge it?
-do i need a battery meter / at which voltage does the save perish?

the first point is pretty easy, these are some options i can think of:
-use a usb cable
-use a solar panel
-modify the gameboy so the cart plugs into a charging connection when inserted

the last option will probably be the most feasible, but needs some more thinking: do i want the battery to be charged constantly?
the answer is no, because it will damage the battery over time. so you need a small switch to enable/disable charging. youll want the cart to be chargeable even when the gameboy is off, so the charging connection of the gameboy should be directly connected to the batteries.
now if you can charge the cart battery at will youll also want to know when you should charge it. this is why we have to know at which voltage the save goes byebye. i dont have the equipment to test that, so ill welcome anybody who would bother to test that for me.
if we know the critical voltage, we can build a battery led that lights up a little while before the critical voltage so we can react and charge the battery. this should be at least a day, so we dont have to stay alert 24/7.
so the voltage tester could either do a lot of measurements to know when the battery still has about a day of charge, or he calculates the power consume of the gameboy cart and from that we calculate the voltage of the day before the voltage drop.

this is a lot of text and im sure its not all in a logical order, but youre very welcome to help smile
when the project is finished we could make a simple tutorial for everybody to copy.

and yes, we will probably have to mod our cartridge, because i highly doubt well find enough room in the cart for all the extra parts (namely the battery, the 3v regulator and the battery meter, the rest could be in the gameboy).

nickmaynard
Offline
rochester, ny

Could be neat. I just back stuff up every few sessions.

yogi
Offline
Jelly Stone park, MD USA

Generally, RAM chips hold their data down to around 2V, but check your data sheet for specifics.
I would suggest that you approach the charging problem with a automatic circuit, charging the battery when the cart is docked. Dallas Semi, and I'm sure others did also, used to make a RAM supervisor chip to control switching from mains to batt.
There is never going to be a 100% fail-safe design; the batts will drain if the cart is left in a box for years, or the batts will fail over time with reg use. Battery backed RAM is not a permanent media, could be why we don't see too many RAM based devcarts.
For truly 'safe' you need to back it up. A batt will buy you some time, but only diamonds are forever.There are some newer chips out that operate as RAM and save to Flash on power fail, but speed and density may be an issue ATM.

Bamboori
Offline
Germany

i dont think id be able to pull off a ram supervisor tongue
as for the failing battery, yes that might become a problem. one could use two batteries in parallel and make an alarm led to see when one dies, and make them accessable with bare hand (under a flip lid or something) and swappable.

yogi
Offline
Jelly Stone park, MD USA

I just brought up the Dallas chip cause this thread reminded me of the last time I work on a similar problem. I'm sure if you look into Maxium;s current lineup you will find a charger/controller chip, these type of circuits are used in every phone/mp3 player/Ipad shipped. The biggest problem is dealing with the SMT packaging, not DIY friendly!
  If you look at the problem from a diff angle, why not a dock to dump the sav data from a stock cart. A uController connected to the cart's bus contacts that reads out the RAM's data, and could also write to it. Throw in a USB connection for control and archiving to HD. I know this is do-able, (it's prob already been done for the GB? )

Bamboori
Offline
Germany

uhm... i dont really get what you mean ._.

Zef
Offline

Yeah, nothing is fool-proof, I had just replaced the batteries on one of my carts so I thought I was safe for a while, but the solder to the battery casing broke loose, so I lost it anyway tongue

Edit: lol, had to do a double take, interesting censorship on this board smile

Last edited by Zef (Jun 20, 2013 3:59 pm)

thebitman
Offline

I've looked into the possibility of throwing FRAM into non-FRAM flashcarts. Still on the fence about whether or not to do it, but technically there are drop-in replacements for chips I have isolated in some of my cartridges. Just want to let you know that option also exists though it has mostly gone unrealized.

Bamboori
Offline
Germany

thats interesting o: but how costly do you think it would be? im not exactly rich and dont have a programmer or anything.

yogi
Offline
Jelly Stone park, MD USA
Bamboori wrote:

uhm... i dont really get what you mean ._.

Well, had the cart reader for the PS1 in mind. Some combination of PC softs and a hardware interface to access the address and data bus on the cart.

Bamboori
Offline
Germany

but wouldnt that basically be a usual gameboy transferer? or did i still not understand you? D:

yogi
Offline
Jelly Stone park, MD USA
thebitman wrote:

I've looked into the possibility of throwing FRAM into non-FRAM flashcarts. Still on the fence about whether or not to do it, but technically there are drop-in replacements for chips I have isolated in some of my cartridges. Just want to let you know that option also exists though it has mostly gone unrealized.

Cool. I had looked at some of Microchip's FRAM not too long ago, but they were serial devices and the offered densities were low compared to similar serial ram devices.

yogi
Offline
Jelly Stone park, MD USA
Bamboori wrote:

but wouldnt that basically be a usual gameboy transferer? or did i still not understand you? D:

Sorry, yes; didn't know bout the transfer dock. total noobie with all things GB. Whatever it's cost, it has to be cheaper then modding a stack of carts?

Bamboori
Offline
Germany

only if you can get it cheap or you have many carts to mod otherwise. ill only have 1 or 3 carts, so ill rather mod them. also, all the transferers only have parrallel plugs, so you have to use an old computer for backing up your saves.

yogi
Offline
Jelly Stone park, MD USA
Bamboori wrote:

only if you can get it cheap or you have many carts to mod otherwise. ill only have 1 or 3 carts, so ill rather mod them. also, all the transferers only have parrallel plugs, so you have to use an old computer for backing up your saves.

True nuff. Sounds like Bitman's insight would be useful, drop in replacement with FRAM, never have to worry bout batteries

thebitman
Offline

What I know is scalped from other people and forums, and looking at spec sheets. The particular chips I have found *should* work but I'm not in a financial situation to try buying extra carts and FRAM units (which are $12+ USD each and they take a while to install).