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Espruino is a JavaScript interpreter for low-power Microcontrollers. This site is both a support community for Espruino and a place to share what you are working on.
@fanoush
Wow, great. I didn't believe you would get the real thing for such price.
If you already opened it and get SWD working then you don't need to get older espruino and mess with DFU and existing firmware unless you bought more than one and want to update next one without taking apart. For SWD just build the latest and flash it like it would be microbit.
As for building you may start from NRF51822DK board which also has 32KB. So just copy this board file to something else and comment out buttons, LEDs and serial mapping and build it.
Before flashing something else you may try to backup whole flash and UICR space via openocd, see e.g. this, you basically run 'flash banks' to verify the memory is seen and then save banks 0 and 1 via 'flash read_bank 0 flash.bin' and 'flash read_bank 1 uicr.bin'. If it fails the flash may be protected and the backup is harder but possible (see e.g. this).
Also still with the default firmware you may try to find out some firmware version and model number somewhere in the menu on the device or h-band app. Or even check for firmware update via the h-band app. With such model number I could try to match the firmware from their update web servers if you can't make backup via SWD or firmware update in the app won't work or won't leave the firmware somewhere on the phone after update.
Firmware is useful for decompiling to figure out e.g. LCD SPI pinout or HR sensor. Otherwise you would need to trace pins on the board.
EDIT:
As for firmware model number, I see in FCC photos that something is also on the board itself, I don't see that part on your photos. The firmware files are named like
VPH_10_00071300_151.ziporVPH_11_00110600_152.zip. The suffix 151 or 152 is unique h-band app model number but there are more zips for same VPH_XX, e.g. VPH 10 has both _151 and _104 which may mean different board or just different firmware branding of same board.