ExtCard
About the ExtCard PCB
ExtCard is an open source PCB design by profdc9, published on GitHub under the CC-BY-SA-4.0 license. It is a 2-layer board measuring 62.2 × 57.2 mm, with 32 components from 12 distinct parts.
Other key parts include the MicroSD_SPI_CD. By type, the board carries 14 resistors, 7 diodes, 4 capacitors, 3 transistors, 2 ICs and 2 connectors.
From the project
A ISA card for PC/XT/AT that has SD storage and SPI/I2C interfaces using a ATMEGA328P
This is a simple card that provides two SD cards as mass storage devices on PC compatibles in an ISA slot. This design is an adaptation of the Apple II version of the card (). For building in the future, it is designed to use only the most common chips: 74HCT32, 74HCT86, 28C64B/27C128/28C256, 82C55A, and ATMEGA328P. It does not use Compactflash format as that is a rather uncommon memory card format at the time of this writing (Oct 2025). The SD card interface is not as fast as a Compactflash card, however, being read through SPI. Hopefully, the components to build this board will be available…
Main components on the ExtCard
ExtCard bill of materials (BOM)
32 components, 12 distinct parts.
| Qty | Part | Footprint | Refs |
|---|---|---|---|
| 2 | MicroSD_SPI_CD | GCT-MEM2055-00-190-01-A | U12, U13 |
| 3 | 2N3906 | TO-92_Inline_Wide | Q1, Q2, Q3 |
| 1 | WIZNET | PinHeader_2x05_P2.54mm_Vertical | J1 |
| 1 | EXTSPI | PinHeader_2x05_P2.54mm_Vertical | J3 |
| 3 | LED | LED_D3.0mm | D3, D5, D7 |
| 4 | 1N4148 | D_DO-35_SOD27_P7.62mm_Horizontal | D4, D6, D8, D9 |
| 3 | 100 nF | C_Disc_D5.0mm_W2.5mm_P5.00mm | C6, C7, C16 |
| 1 | 10 uF | CP_Radial_D5.0mm_P2.00mm | C17 |
| 4 | 10k | R_Axial_DIN0207_L6.3mm_D2.5mm_P7.62mm_Horizontal | R1, R4, R31, R33 |
| 3 | 100k | R_Axial_DIN0207_L6.3mm_D2.5mm_P7.62mm_Horizontal | R2, R3, R5 |
| 2 | 470R | R_Axial_DIN0207_L6.3mm_D2.5mm_P7.62mm_Horizontal | R21, R24 |
| 5 | 1k | R_Axial_DIN0207_L6.3mm_D2.5mm_P7.62mm_Horizontal | R22, R23, R25, R30, R32 |
ExtCard design files
The KiCad project lives in the profdc9/ISACard repository on GitHub; these links point at the commit this page was built from.
- LayoutExtCard/ExtCard.kicad_pcb
- SchematicExtCard/ExtCard.kicad_sch
ExtCard: common questions
How big is the ExtCard PCB?
The ExtCard measures 62.2 × 57.2 mm, has 2 copper layers and is 1.6 mm thick.
How many components are on the ExtCard?
32 components, from 12 distinct parts. The full bill of materials is listed on this page.
Where can I download the ExtCard design files?
From the profdc9/ISACard repository on GitHub, which has the KiCad layout and the schematic; the links under Design files point to each one.
Can I use the ExtCard design in my own project?
Yes, under the terms of its CC-BY-SA-4.0 license, which profdc9 chose for the repository.
