Velleman

for MK158 downloads click here
Briefly - power in is 9V on the left most two connectors. Power input is diode protected.
Reason for mentioning this kit is that the kit is already made and can be used for testing other gadgets.
The data format is 2400/N/8/1 { RS 232 }.

Useful as a small display board, 3V supply, no serial I/O pmk 157

mk158
check for assembly manual and user manual.