Zx81-external eprom

zxinfo-diy-electronics·zx81-external-eprom

Zx81-external eprom PCB layout, top view — open source board by zxinfo-diy-electronics

About the Zx81-external eprom PCB

Zx81-external eprom is an open source PCB design by zxinfo-diy-electronics, published on GitHub. It is a 2-layer board measuring 60.3 × 52.4 mm, with 13 components from 9 distinct parts.

Other key parts include the W27C512, 74LS138 and 74LS157. By type, the board carries 4 resistors, 3 ICs, 3 capacitors, 1 transistor, 1 connector and 1 switch.

It belongs with the retro computing designs in this gallery.

From the project

External MultiROM Interface based on EEPROM W27C512 for ZX81

BOM for v1.0: - [ ] WINBOND W27C512 EEPROM - [ ] 74LS138 - [ ] 3 x 10K Resistors - [ ] BC549 Transistor - [ ] 2 x 100nF ceramic capacitor, 2,5mm - [ ] DIP Switch 3 x ON-OFF - [ ] Sockets for IC, Edge Connector (RM 2,54)

The PCB can be fitted with a standard Edge Connector for ZX81, or it can be used as a plug-in card in the Bus Extender

- DIP-4 (right) - sets the mode of operation, DOWN = use 8KiB banks, UP = use 16KiB banks - DIP-1 to 3, selects which banks is used as ROM - in case of 16KiB banking, DIP-3 (A13) is ignored.

Main components on the Zx81-external eprom

W27C512 74LS138 74LS157

Zx81-external eprom bill of materials (BOM)

13 components, 9 distinct parts.

Qty	Part	Footprint	Refs
1	W27C512	DIP-28_W15.24mm	U1
1	74LS138	DIP-16_W7.62mm	U2
1	74LS157	DIP-16_W7.62mm	U3
1	BC549	TO-92_Inline	Q1
1	Connector ZX81	EDGE ZX81 BOTTOM	J1
1	SW_DIP_x04	SW_DIP_SPSTx04_Slide_6.7x11.72mm_W7.62mm_P2.54mm_LowProfile	SW2
3	100nF	C_Disc_D3.0mm_W1.6mm_P2.50mm	C1, C2, C3
3	10K	R_Axial_DIN0207_L6.3mm_D2.5mm_P10.16mm_Horizontal	R1, R2, R3
1	4K7	R_Axial_DIN0207_L6.3mm_D2.5mm_P10.16mm_Horizontal	R4

Zx81-external eprom design files

The KiCad project lives in the zxinfo-diy-electronics/zx81-external-eprom repository on GitHub; these links point at the commit this page was built from.

Layoutzx81-external-eprom.kicad_pcb
Schematiczx81-external-eprom.kicad_sch

Zx81-external eprom: common questions

How big is the Zx81-external eprom PCB?

The Zx81-external eprom measures 60.3 × 52.4 mm, has 2 copper layers and is 1.6 mm thick.

How many components are on the Zx81-external eprom?

13 components, from 9 distinct parts. The full bill of materials is listed on this page.

Where can I download the Zx81-external eprom design files?

From the zxinfo-diy-electronics/zx81-external-eprom repository on GitHub, which has the KiCad layout and the schematic; the links under Design files point to each one.

Can I use the Zx81-external eprom design in my own project?

The repository has no license, so all rights stay with zxinfo-diy-electronics. Use it as a reference, and ask the author before reusing the design.

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