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68k nano watchdog

demik·oldworld·EDA/68k-nano-wd/68k-nano-wd.kicad_pcb

68k nano watchdog PCB layout, top view — open source AVR/Arduino board by demik
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About the 68k nano watchdog PCB

68k nano watchdog is an open source AVR/Arduino PCB design by demik, published on GitHub under the CERN-OHL-P-2.0 license. It is a 2-layer board measuring 90.2 × 26 mm, with 13 components from 11 distinct parts.

Its main chip is the LF347, from the AVR/Arduino family. Other key parts include the CD40107BE. By type, the board carries 4 resistors, 2 ICs, 2 connectors, 2 diodes, 2 capacitors and 1 switch.

It belongs with the retro computing designs in this gallery.

From the project

Development ressources for Old World Macintosh (68k and NuBus PPC) and a few related things…

Minimalistic watchdog build around an ATtiny45 for the 68k-nano(+).

- generate an external 10 Hz interrupt for FUZIX if running without an RTC - monitor RAM accesses and enable a LED if no access have been done for a few seconds (crash)

The 68k nano watchdog hardware is very simple and straightforward. It can be built on a breadboard as well.

As of this writing (June 2026), all components are available from major distributors like Mouser and Jameco.

68k nano watchdog, from the project README
From the project README

Main components on the 68k nano watchdog

LF347CD40107BE

68k nano watchdog bill of materials (BOM)

13 components, 11 distinct parts — part numbers from the project's BOM.

QtyPartRefs
1
LF347
ATtiny45-20P
U1
1
CD40107BE
U2
1
CONN_01X02
EXPANSION (F.Cu)
J5
1
SJ1-3535NG-BE
EXPANSION (B.Cu)
J6
1
CLOCK_SW
SW1
1
CLOCK
D1
1
WATCHDOG
D2
2
100NF
0.1uF
C1, C2
2
1k*
R1, R2
1
10K
10k
R3
1
20K
10k
R4

68k nano watchdog design files

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

68k nano watchdog: common questions

What microcontroller does the 68k nano watchdog use?

The 68k nano watchdog is built around the LF347, from the AVR/Arduino family.

How big is the 68k nano watchdog PCB?

The 68k nano watchdog measures 90.2 × 26 mm, has 2 copper layers and is 1.6 mm thick.

How many components are on the 68k nano watchdog?

13 components, from 11 distinct parts, with part numbers taken from the project's own BOM. The full bill of materials is listed on this page.

Where can I download the 68k nano watchdog design files?

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

Can I use the 68k nano watchdog design in my own project?

Yes, under the terms of its CERN-OHL-P-2.0 license, which demik chose for the repository.

Can I test firmware for the 68k nano watchdog without the hardware?

Yes. HardLabs builds a simulation of the board from its netlist and BOM, so you can run and debug AVR/Arduino firmware against it before you order a PCB.

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