Picture of Switchable Dual-Voltage (3.3v/5v) Hacduino
This is my second version of a Hackduino. I built the first one on
a Radio Shack PC board (solderable breadboard) with a triple-pad IC
layout. It turned out to be, essentially, an Arduino Duemilanove clone,
complete with headers for plugging in shields. The result was more than
satisfactory, but I needed a denser parts layout this time.

I wanted a Hackduino that would run at 3.3 volts (but retaining 5 volt compatibility),
which would permit direct interfacing with 3.3v sensors and peripherals
(and with a Raspberry Pi!) without having to use level shifters.
It would be also be nice to have an on-board plug-in socket for a Nokia 5110 display,
since that (allegedly) runs on 3.3v. Headers for shields were superfluous because I
already had laying around quite a number of factory-built Arduinos that
would serve that purpose. Result: a tailor-made special purpose Hackduino.
Let's call it a Hacduino.

I build this one on a stripboard and that proved to be more suitable
than a solderable breadboard for a dense and efficient parts layout.
It's especially useful when there are terminal points with multiple

Features of the Mark II Hacduino:
  1. On/off power switch
  2. Switchable between 3.3v and 5v to the Vcc buss (& voltage indicator?)
  3. D13 LED can be enabled/disabled by a jumper
  4. Wired on-board socket for a Nokia 5110 monochrome display
  5. Uses standard (cheap) hole-through ATMega328 chip
  6. Highly customizable -- can optionally add extra header strips for power and I/O.


An ATMega 328 powered at 3.3 volts with a 16 MHz clock is running out
of spec. Effectively, it is overclocked. I have not had any problems with
this, but I certainly would not run an overclocked CPU on mission critical
projects, such as controlling industrial machinery or even home automation.
For hobby purposes, it should be just fine, though.

thegrendel (author) 1 year ago
If anyone is interested in the Arduino sketch for interfacing
this Hacduino to the Mighty Ohm geiger counter mentioned in the final step,
see the last two posts in this forum thread.