Another console which i always wanted to design my own flashcart for, the GameKing from Timetop.
The frontside contains the eeprom and six switches, the backside contains a description for all switches on the board.
This flashcart has 512kb of space and is switchable between 1x 512kb bank or 4x128kb banks.
Which means you can program 4 games with 128kb to it, or just one of those 4in1 roms, which have 512kb.
The cartridge is reprogramable with every programmer which supports 39VF040 eeproms. For example the cheap TL866IIPlus (costs about 35-40EUR) can do the job easily. Programming a 512kb rom takes about 25seconds.
The goal of this cartridge-design was to be as small as possible, while also as much useable as possible.
The cartridge itself should also work within the GameKing3 to play the GK1 and GK3 games on it. As with the recent emulation progress of the GameKing and GameKing3 (emulated in the next MAME-release) it was determined that the GameKing3 makes some checks about flashroms at it's startup. Which could be a protection-check.
Because of this fact, i would need someone with an GameKing3 to verify, if this cartridge is really working on a GK3 handheld. (This person will get a discount on the cartridge!)
I currently have 9 pieces of this cartridge left.
One cartridge can get bought for 15EUR.