Readiness report

Gigatron TTL Microcomputer · 2026-07-09 12:55 · complete · 53 searches, 0 pages fetched

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Readiness: Gigatron TTL Microcomputer

Verdict: Ready with caveats · 2026-07-09 · est. parts cost $115–$140

The Gigatron TTL Microcomputer is buildable as a cold check of the market on 2026-07-09. Over 90% of the bill of materials consists of standard 74HCT logic, resistors, and capacitors in high-volume production. However, two items present significant sourcing challenges: the 6.25 MHz crystal (a non-standard frequency) and the original wooden enclosure (discontinued). The crystal requires sourcing from specialized vendors or surplus markets, while the enclosure must be fabricated via DIY methods using community-provided design files.

Action required

Part Problem Recommended action
74HCT04 Planned SN74HCT04N out of stock at primary distributor. Source CD74HCT04E or use Mouser for the original part.
62256 LY62256PL-55LLI is unavailable at major distributors. Use Alliance Memory AS6C62256-55PCN as a direct replacement.
Quartz Crystal 6.25 MHz (MP062-E) is out of stock at major distributors. Source Parallax part 251-06250 or equivalent from specialized eBay/surplus vendors.
DB9 Male 5747840-3 is out of stock. Use Assmann A-DS 09 A/KG-T2S as a direct substitute.
Wooden Enclosure Commercial manufacturing has ceased. Download community OpenSCAD or SVG plans for DIY laser cutting or woodworking.

Parts

1. Integrated Circuits (Main Board)

Part Spec/Package Status Stock Price Source
74HCT04 Hex Inverter, DIP-14 Available 0 $0.68 Mouser
74HCT161 4-bit Counter, DIP-16 Ready 9,716 $1.34 DigiKey
74HCT273 Octal Register, DIP-20 Ready 28,789 $0.93 DigiKey
74HCT244 Octal Bus Driver, DIP-20 Ready 4,495 $1.52 DigiKey
74HCT139 Dual 2-to-4 Decoder, DIP-16 Ready 26,336 $1.19 DigiKey
74HCT153 Dual 4-to-1 MUX, DIP-16 Ready 840 $1.22 DigiKey
74HCT138 3-to-8 Decoder, DIP-16 Ready 3,447 $0.89 DigiKey
74HCT240 Octal Inv Buffer, DIP-20 Ready 24,089 $0.96 DigiKey
74HCT32 Quad OR Gate, DIP-14 Ready 1,806 $0.97 DigiKey
74HCT283 4-bit Full Adder, DIP-16 Ready 923 $1.32 DigiKey
74HCT377 Octal Flip-Flop, DIP-20 Ready 10,109 $1.43 DigiKey
74HCT157 Quad 2-to-1 MUX, DIP-16 Ready 33,788 $1.16 DigiKey
74HC595 8-bit Shift Reg, DIP-16 Ready 16,021 $1.86 DigiKey
62256 32K x 8 SRAM, DIP-28 At risk 0 — —
27C1024 1Mbit EPROM, DIP-40 Low Stock 96 $4.52 DigiKey
MCP100-450DI/TO Reset IC, TO-92 Ready 8,797 $0.42 DigiKey

2. Pluggy McPlugface (Add-on) ICs

Part Spec/Package Status Stock Price Source
ATtiny85-20PU MCU, DIP-8 Ready 25,981 $1.66 DigiKey

3. Passive Components (Main Board)

Part Spec/Package Status Stock Price Source
Resistor 68 Ω Axial, 1/4W Ready 23,623 $0.10 DigiKey
Resistor 750 Ω Axial, 1/4W Ready 20,724 $0.10 DigiKey
Resistor 1 kΩ Axial, 1/4W Ready 730,687 $0.10 DigiKey
Resistor 1.5 kΩ Axial, 1/4W Ready 26,645 $0.10 DigiKey
Resistor 2.2 kΩ Axial, 1/4W Ready 51,599 $0.10 DigiKey
Resistor 1 MΩ Axial, 1/4W Ready 592,309 $0.10 DigiKey
Resistor Array 5-pin SIP, 2.2 kΩ Low Stock 32 $0.28 DigiKey
R2R Network 6-pin SIP, 10 kΩ Ready 1,368 $0.46 DigiKey
Capacitor 47 pF Ceramic, 50V Ready 24,946 $0.26 DigiKey
Capacitor 100 nF Ceramic, 50V Ready 236,488 $0.27 DigiKey
Capacitor 220 µF Electrolytic, 25V Ready 7,630 $0.60 DigiKey

4. Discrete Semiconductors and Protection

Part Spec/Package Status Stock Price Source
Signal Diode BAT42, DO-35 Ready 23,163 $0.50 DigiKey
Zener Diode 5.6V 5W, DO-15 Ready 70,621 $1.26 DigiKey
LED Red, 3mm 1.8V, 2mA Ready 61,796 $0.51 DigiKey
Multifuse (PTC) 0.75A 60V, Radial Ready 5,227 $0.47 DigiKey
Quartz Crystal 6.25 MHz, HC-49/U At risk 0 — —

5. Connectors and Hardware

Part Spec/Package Status Stock Price Source
Mini-USB Type B, 5-pin Ready 1,061 $2.07 DigiKey
3.5mm Audio Jack Stereo, TH Ready 234,594 $1.06 DigiKey
DB15 Female (VGA) High Density, R/A Ready 128 $2.07 DigiKey
DB9 Male Standard, R/A At risk 0 — —
Mini-DIN 6-pin PS/2, TH Ready 4,184 $1.88 DigiKey
DB9 Female Standard, TH Ready 1,465 $1.24 DigiKey
IC Sockets DIP Assortment Ready High [$6.00](https://www.google.com/search?ibp=oshop&q=DIP IC socket assortment&prds=productid:4697472611069187389) [Shades Dancewear](https://www.google.com/search?ibp=oshop&q=DIP IC socket assortment&prds=productid:4697472611069187389)
Famicom Gamepad Clone, DB9 Ready High [$4.95](https://www.google.com/search?ibp=oshop&q=Famicom DB9 clone controller&prds=productid:10938543824438340543) [AliExpress](https://www.google.com/search?ibp=oshop&q=Famicom DB9 clone controller&prds=productid:10938543824438340543)
Wooden Enclosure Custom Case Obsolete — — —
Rubber Feet 3M Bumpons Ready High $14.70 DigiKey

Substitutes

For part Substitute Differences Judgment
74HCT04 CD74HCT04E Direct PDIP substitute. Acceptable.
62256 Alliance Memory AS6C62256-55PCN Direct replacement (DIP-28, 55ns). Acceptable.
DB9 Male Assmann A-DS 09 A/KG-T2S Similar direct substitute footprint. Acceptable.

Verify any substitute against its datasheet before ordering.

Other dependencies

  • Main ROM: Requires 27C1024 EPROM programmed with Gigatron ROM v5. (Ready)
  • BabelFish Firmware: Requires ATtiny85 programmed with BabelFish interface software. (Ready)
  • PCB Fabrication: Requires Gerber files for Main and Pluggy boards from gigatron.io. (Ready)
  • Enclosure Plans: DIY OpenSCAD/SVG files found via Thingiverse and community sites. (Ready)

Watch list

  • AT27C1024-70PU: This 16-bit EPROM is increasingly rare (only 96 units in stock); procure immediately or investigate SST27SF010 adapters for future builds.
  • 6.25 MHz Crystal: No longer available via standard distribution channels; rely on specialized surplus or Parallax stock.
  • Resistor Array (4605X-101-222LF): Extremely low stock (32 units). Consider 4605X-101-222LF substitutes from other manufacturers if stock depletes.