2 layers232.8 × 204.2 mm
2 layers118.5 × 100.4 mm
Hardmpu
christal87/hardmpuHardMPU PCB design based on the original schematic
- Size
- 118.5 × 100.4 mm
- Copper layers
- 2
- Thickness
- 1.6 mm
- Parts
- 44
- Nets
- 86
- Pads
- 355
- Tracks, vias
- 1,279, 83
- Routed
- Yes
- KiCad
- KiCad 5 (file 20171130)
- Created
- 9 Jun 2026
- Updated
- 9 Jun 2026
Overview
Hardmpu is an open-source printed circuit board by christal87, from the christal87/hardmpu repository on GitHub, published under the GPL-3.0 licence. It is a 2-layer board of 118.5 × 100.4 mm with 44 parts on 86 nets, routed with 1,279 tracks and 83 vias.
It is built around the ATMEGA1284P-PU, 74LS240DC and 74LS374PC, with the 74LS74PC among its other parts. Its parts include 14 capacitors, 10 ICs, 8 resistors, 7 connectors and 1 diode. It belongs with the AVR (ATmega, ATtiny) boards of this library.
Main components
4
ATMEGA1284P-PU
PDIP-40-40℃~+85℃ 1.8V~5.5V 10bit 128KB 16KB 20MHz 32 4KB 8 Bit AVR Built-in FLASH PDIP-40 Microcontrollers (MCU/MPU/SOC) ROHSMicrochip TechnologyMicrocontrollers (MCU/MPU/SOC)74LS240DC
--55℃~+125℃ 1 15mA 18ns@5V,45pF 24mA 29mA 4.75V~5.25V 74LS Output enable Schmitt trigger Tri-State - Buffers, Drivers, Receivers, TransceiversTexas InstrumentsBuffers, Drivers, Receivers, Transceivers
74LS374PC
PDIP-200ns 0℃~+70℃ 1 20ns 28ns@5V,45pF 35MHz 4.75V~5.25V 45mA 74LS Series 8 D-Type Rising Edge Tri-State PDIP-20 Flip FlopsonsemiFlip Flops
74LS74PC
DIP-140ns 0℃~+70℃ 1 2 20MHz 3.5pF 35ns@5V,50pF 4.5ns 4.75V~5.25V 400uA 74LS Series 8mA 8mA Asynchronous Complementary D-Type Rising Edge Set and Reset DIP-14 Flip FlopsTexas InstrumentsFlip Flops
README
README.mdhardmpu
A HardMPU 8-bits wide ISA card PCB based on ab0tj's schematic. I was curious how ISA cards were designed back in the day and I'm also a retro PC enthusiast so I designed my own version a few years ago. I also used this project as an experiment to supplement and speed up a manual ECAD design flow using FreeRouting. After drawing an outline and placing components I let it run multiple iterations/optimizations then I chose one of it's suitable outputs as a template to refine manually afterwards. There are two label typos that slipped through invisibly ERC/DRC reporting stages which got corrected using bodge wires as a temporary fix (see photos). I've chosen an I/O bracket backplate that seemed to be popular and was readily available from multiple sources on Aliexpress at design time. Just like the original project, this circuit design is covered by the GPL-3.0 license and is free for non-commercial use.
Parts
44| Qty | Value | Footprint | References |
|---|---|---|---|
| 11 | 0.1uF | Capacitor_THT:C_Disc_D3.4mm_W2.1mm_P2.50mm | C3, C5, C6, C7, C8, C9, C10, C11, C12, C13, C14 |
| 3 | 220R | Resistor_THT:R_Axial_DIN0207_L6.3mm_D2.5mm_P7.62mm_Horizontal | R4, R5, R6 |
| 3 | 4.7k | Resistor_THT:R_Axial_DIN0207_L6.3mm_D2.5mm_P7.62mm_Horizontal | R1, R2, R3 |
| 2 | 18pF | Capacitor_THT:C_Disc_D5.0mm_W2.5mm_P5.00mm | C1, C2 |
| 2 | 74LS138 | Package_DIP:DIP-16_W7.62mm_Socket_LongPads | U1, U2 |
| 2 | 74LS374 | Package_DIP:DIP-20_W7.62mm_Socket_LongPads | U4, U5 |
| 2 | 74LS74 | Package_DIP:DIP-14_W7.62mm_Socket_LongPads | U7, U8 |
| 1 | 1N4148 | Diode_THT:D_DO-35_SOD27_P7.62mm_Horizontal | D1 |
| 1 | 20MHz | Crystal:Crystal_HC49-U_Vertical | X1 |
| 1 | 220k | Resistor_THT:R_Axial_DIN0207_L6.3mm_D2.5mm_P7.62mm_Horizontal | R7 |
| 1 | 3.3k | Resistor_THT:R_Axial_DIN0207_L6.3mm_D2.5mm_P7.62mm_Horizontal | R8 |
| 1 | 33uF | Capacitor_THT:C_Disc_D5.0mm_W2.5mm_P2.50mm | C4 |
| 1 | 500mA | Fuse:Fuseholder_TR5_Littelfuse_No560_No460 | F1 |
| 1 | 6N136 | Package_DIP:DIP-8_W7.62mm_Socket_LongPads | IC2 |
| 1 | 74LS08 | Package_DIP:DIP-14_W7.62mm_Socket_LongPads | U3 |
| 1 | 74LS240 | Package_DIP:DIP-20_W7.62mm_Socket_LongPads | U6 |
| 1 | 8bit Wide ISA Bus | Connector_PCBEdge:ISA_CARD_EDGE_CONNECTOR_8BIT_Rev0 | BUS1 |
| 1 | ATmega1284P-PU | Package_DIP:DIP-40_W15.24mm_Socket_LongPads | IC1 |
| 1 | DB9 | Connector_Dsub:DSUB-9_Female_Horizontal_P2.77x2.84mm_EdgePinOffset7.70mm_Housed_MountingHolesOffset9.12mm | J1 |
| 1 | IRQ | Connector_PinHeader_2.54mm:PinHeader_2x06_P2.54mm_Vertical | P2 |
| 1 | ISP | Connector_PinHeader_2.54mm:PinHeader_2x03_P2.54mm_Vertical | P3 |
| 1 | JTAG | Connector_PinHeader_2.54mm:PinHeader_2x05_P2.54mm_Vertical | P4 |
| 1 | PORT | Connector_PinHeader_2.54mm:PinHeader_2x04_P2.54mm_Vertical | P1 |
| 1 | SHIELD_GND | Connector_PinHeader_2.54mm:PinHeader_1x02_P2.54mm_Vertical | P6 |
| 1 | USER | Connector_PinHeader_2.54mm:PinHeader_2x05_P2.54mm_Vertical | P5 |
The 43 most common of 44 parts.
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Questions
How big is the Hardmpu PCB?
It measures 118.5 × 100.4 mm and has 2 copper layers, 1.6 mm thick.
What parts does the Hardmpu use?
44 parts, built around the ATMEGA1284P-PU, 74LS240DC, 74LS374PC and 74LS74PC. The full list of its parts is on this page, with links to each part's symbol and footprint where PCBKit's library has them.
Where can I download the Hardmpu KiCad files?
From the christal87/hardmpu repository on GitHub, at the commit this page was made from: the board is HardMPU.kicad_pcb. PCBKit opens the board in the browser, with nothing to install.
Can I use the Hardmpu design in my own project?
Its repository publishes it under the GPL-3.0 licence: you may reuse it on that licence's terms (keep the author's notice, and for a copyleft licence share your changes alike).