KiCad design files for a bidirectional 3.3V-to-5V level converter shield that sits between an Arduino Giga R1 WiFi and a RetroShield Z80. The shield translates all bus signals between the Giga's 3.3V logic and the RetroShield's 5V logic.
The shield uses nine TXB0108PW 8-bit bidirectional level converter ICs, providing 72 channels of voltage translation. The TXB0108 uses automatic direction sensing — it detects which side is driving each signal and translates accordingly.
Board specifications:
- Dimensions: 155mm x 90mm (matches Arduino Giga R1 footprint)
- Layers: 2-layer PCB
- Level shifter ICs: 9x TXB0108PW (TSSOP-20)
- Signals translated: 72 channels covering data bus, address bus, and control signals
- Version: V0.1
| Signal Group | Pins | Channels | Direction |
|---|---|---|---|
| Data bus D0–D7 | D42–D49 | 8 | Bidirectional |
| Address bus A0–A7 | D22–D29 | 8 | Z80 → Arduino (input) |
| Address bus A8–A15 | D30–D37 | 8 | Z80 → Arduino (input) |
| Control (MREQ, WR, IORQ, RD) | D39–D41, D53 | 4 | Z80 → Arduino (input) |
| Control (RESET, INT, NMI, CLK) | D38, D50–D52 | 4 | Arduino → Z80 (output) |
| Remaining GPIO | Various | 40 | Bidirectional |
The TXB0108's auto-direction sensing fails for some Z80 bus signals in practice:
- IORQ_N (pin 39) — stuck HIGH; never toggles through the converter
- RD_N (pin 53) — stuck HIGH; never toggles through the converter
- Data bus Z80→Arduino — invisible during I/O write cycles
These failures are worked around in firmware via shadow register tracking. See the companion firmware project for details.
kicad/ KiCad 8 source files
├── AlexJ_bz_ArduinoGigaShield.kicad_pro Project file
├── AlexJ_bz_ArduinoGigaShield.kicad_sch Schematic
├── AlexJ_bz_ArduinoGigaShield.kicad_pcb PCB layout
└── AlexJ_bz_ArduinoGigaShield.kicad_prl Project preferences
gerber/ Production-ready Gerber files
├── *-F_Cu.gbr Front copper
├── *-B_Cu.gbr Back copper
├── *-F_Mask.gbr Front solder mask
├── *-B_Mask.gbr Back solder mask
├── *-F_Silkscreen.gbr Front silkscreen
├── *-B_Silkscreen.gbr Back silkscreen
├── *-F_Paste.gbr Front paste (for stencil)
├── *-B_Paste.gbr Back paste
├── *-Edge_Cuts.gbr Board outline
├── *-PTH.drl Plated through-hole drill
├── *-NPTH.drl Non-plated through-hole drill
└── *-job.gbrjob Gerber job file
bom/ Bill of Materials
├── AlexJ_bz_ArduinoGigaShield.csv CSV format
└── AlexJ_bz_ArduinoGigaShield.xlsx Excel format
cpl/ Component Placement
└── AlexJ_bz_ArduinoGigaShield-all-pos.csv Pick & place positions
schematic/ Schematic PDF
└── AlexJ_bz_ArduinoGigaShield.pdf
images/ 3D renders
├── AlexJ_bz_ArduinoGigaShield_TOP.jpg Top view
├── AlexJ_bz_ArduinoGigaShield_TOP.png Top view (PNG)
├── AlexJ_bz_ArduinoGigaShield_BTM.jpg Bottom view
└── AlexJ_bz_ArduinoGigaShield.png Perspective view
| Reference | Qty | Value | Part Number | Package |
|---|---|---|---|---|
| U1–U9 | 9 | TXB0108PW | TXB0108PWR | TSSOP-20 |
| C1–C27 | 27 | 0.1 uF | CC0603KRX7R9BB104 | 0603 |
| R1–R9 | 9 | 10K | RC0603FR-0710KL | 0603 |
Each TXB0108 has a 0.1 uF decoupling capacitor on both VCCA (3.3V) and VCCB (5V) power pins. The 10K pull-up resistors tie the OE (Output Enable) pins to 3.3V.
The Gerber files in gerber/ can be uploaded directly to any PCB fabrication service:
For SMD assembly, provide the BOM (bom/) and component placement file (cpl/) to the fab house.
| Parameter | Value |
|---|---|
| Layers | 2 |
| Board thickness | 1.6 mm |
| Copper weight | 1 oz |
| Surface finish | HASL or ENIG |
| Solder mask | Red (or your preference) |
| Silkscreen | White |
- SMD components first — solder the TXB0108PW ICs, decoupling capacitors, and pull-up resistors
- Pin headers last — solder the through-hole pin headers (female on bottom for the Giga, male on top for the RetroShield)
- Power jumper — a jumper wire connects the Giga's 3.3V output to the shield's VCCA rail (visible in assembly photos)
- Orientation — the shield silkscreen is labeled "ARDUINO GIGA R1 SHIELD V0.1" with pin numbers matching the Giga's header layout
- retroshield-z80-cpm-giga — Arduino Giga R1 firmware for CP/M 2.2 on the RetroShield Z80
- retroshield-sector-server — Rust TCP server for WiFi-based CP/M disk I/O
This project is documented in a three-part series on tinycomputers.io:
- My Experience Using Fiverr for Custom PCB Design: A $468 Arduino Giga Shield
- Porting CP/M to the Arduino Giga R1: When Level Converters Fight Back
- Playing Zork on a Real Z80: From CP/M Boot to the Great Underground Empire
This work is licensed under the Creative Commons Attribution-ShareAlike 4.0 International License (CC BY-SA 4.0). See LICENSE.
You are free to share and adapt this design, including for commercial purposes, as long as you give appropriate credit and distribute derivative works under the same license.
Alex Jokela — tinycomputers.io
PCB design by Elijah (ekeziah) via Fiverr. Manufacturing sponsored by PCBWay.