The Amstrad ROM Expansion was published 1988 in the Practical Electronics magazine by Simon Dean. It is possible to use up to six expansion ROMs (16 kB each) with the board. Because there are only a few parts needed, the price of the board is inexpensive.
Part List
R1 620 Ohm 0.25W C1-C6 100nF ceramic C7 22uF elect IC1 74LS32 IC2 74LS373 IC3 74LS138 IC4 74LS02 IC5 74LS20 D1 1N4148