Help for Build Super Famicom (rom loading from usb cartridge)

Nounours

Hello Everyone,

This is my first message on this Forum and i am totally newbie on the raspberry / retropie scene. However, after all my research and the review of a lot of thread related to this topic, i think i am finally ready o start my own project.
Nothing especially original but i want to make my own super famicom build (my old one doesn't work anymore so i can use it for the case, no need to new buy one, and in case a want another stock one, there is a lot of super famicom here in japan : o ) .

Here is below what i plan to do :

Keep the case as stock as possible
raspberry pi 3b based
functional snes controller port.
Usb port on the back to connect other controller if needed
power switch functional to turn on/off the raspberry using the mausberry circuit (on his way...)
reset button to exit the game and come back to the main menu
functional cartridge slot => the goal is to load the roms from cartridge and to have one cartridge dedicated with the rom of one specific hardware i want to emulate (1 cartridge for SNES, one for Nes, one for megadrive etc... In order to keep a little this particular feeling with the cartridge change).

And my main question will be for the last point. i think i already have all my answer for all the previous point just by looking on all the thread did for this kind of build. However the last one is a little bit tricky for me.
i don't know how to make a good solder / select the good pin for soldering the usb drive to the cartridge. and also how to connect the cartridge slot to the raspberry.
If my idea is not clear, that guy on youtube made what i want to achieve but with a Nes case, so it maybe a little bit different regarding the cartridge slot :

Can you advise me on how to select make the connection to have this cartridge slot idea functional ?

Many thanks in advance for your help.
And sorry for the bad english

Darksavior

@nounours You'll need soldering experience to solder 4 pins of your choice on the cart slot, to match the 4 pins on the cart. A multimeter is highly recommended for the cart to figure out what pins go to what. Here's pics of mine for reference. The last pic has the connections exposed. grey wires are for the two pads that goto gpio, blue/yellow for reset. blue usb cord soldered to 4 cart slot pins.
https://www.dropbox.com/sh/pc27fe31cruc4q4/AADWrnunXI4jrt0qIkQLkUAja

Nounours

Thank you ! i guess i will buy a multimeter asap. It is helpful for me to see how you did your soldering.

However, i'am sorry because it will be a really naive question, i am not sure to know what i should see with the multimeter in order to be sure the pins of the cart are matching with the pins of the slot.

Darksavior

@nounours You'll be looking for continuity from the traces on the cart pcb. You'll also have to desolder chips or remove them from the circuit by scratching out the traces or they'll interfere. You need a clear trace or the USB stick will be hard to read.

Look at the pic of my cart. Traces go from the front of the cart to the back and to the front again. Try and find the 4 shortest traces for less interference. Thats what the multimeter will do to make your life easier. If it beeps from one end to the other then it should work.

There are solder points very near to the cart pins too. You can use those but you must use the same pins for all the carts, of course. Depending on the cart, those might be the best to use. Here is an example. 4 short traces. Then the traces are scratched out from the back out so they're cut off from the rest of the circuit for less interefence.