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Add sub

tmarhguy·alu·schematics/kicad/boards/add_sub/add_sub.kicad_pcb

Add sub PCB layout, top view — open source board by tmarhguy
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About the Add sub PCB

Add sub is an open source PCB design by tmarhguy, published on GitHub under the MIT license. It is a 2-layer board measuring 110 × 117 mm, with 200 components from 8 distinct parts.

Other key parts include the 74HC86 and 74HC157. By type, the board carries 178 transistors, 12 ICs, 6 capacitors and 4 connectors.

From the project

8-bit combinational ALU built from scratch with 3,488 CMOS transistors (KiCad + SPICE + Logisim + 1.24M tests

8-bit adder with conditional B inversion for subtraction

Implements both addition and subtraction using a single 8-bit ripple-carry adder.

Operations: - ADD: OUT = A + B (when M=0) - SUB: OUT = A - B (when M=1, using 2's complement)

Truth table: | M | B | B' | |---|---|----| | 0 | 0 | 0 | | 0 | 1 | 1 | | 1 | 0 | 1 | | 1 | 1 | 0 |

When M=0 (ADD): B' = B When M=1 (SUB): B' = ~B

Main components on the Add sub

74HC8674HC157

Add sub bill of materials (BOM)

200 components, 8 distinct parts.

QtyPartRefs
4
74HC86
U201, U1101, U2201, U3301
2
74HC86
U701, U702
6
74HC157
U801, U802, U803, U804, U805, U806
89
NMOS
Q301, Q304, Q306, Q308, Q502, Q602, Q701, Q704 +81
89
PMOS
Q302, Q303, Q305, Q307, Q501, Q601, Q702, Q703 +81
3
Conn_01x12_Pin
J101, J103, J104
1
Conn_01x34_Pin
J102
6
100nF
C201, C701, C702, C1101, C2201, C3301

Add sub design files

The KiCad project lives in the tmarhguy/alu repository on GitHub; these links point at the commit this page was built from.

Add sub: common questions

How big is the Add sub PCB?

The Add sub measures 110 × 117 mm, has 2 copper layers and is 1.6 mm thick.

How many components are on the Add sub?

200 components, from 8 distinct parts. The full bill of materials is listed on this page.

Where can I download the Add sub design files?

From the tmarhguy/alu repository on GitHub, which has the KiCad layout and the schematic; the links under Design files point to each one.

Can I use the Add sub design in my own project?

Yes, under the terms of its MIT license, which tmarhguy chose for the repository.

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