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The Radiac 2000

A Desktop Geiger Counter
by Sam Evans

The Radiac 2000

What can be said of the Radiac 2000?

It started out as a portable GM counter based on my HV circuit, and John
Iovine's early version (circa 2004) of the Digital Meter adapter. After the PCB
was built I decided to make it a desktop counter. It is really the Radiac 2000
Mark-1 as I am planning at some stage to redo the PCB using surface mount
technology and include all subunits on the one PCB, such as main power board and
audio amplifier - Radiac Mark-2. I am also looking at the possibility of using
the Radiac 2000 Mark-2 with both a GM-tube and a Scintillator tube with some
modifications to the HV circuit, and this would be the Radiac 2000 Mark-3. The
PCB is made from FR-4 single-sided fibre-glass board with 2 ounce/foot of copper
laminate. As an added protection the board was coated with a layer of DCA - SCC3
Conformal Coating, and subjected to 12 hours at 25°C followed by 24 hours at
90°C. I like things to last a long time and I do not like cluttered PCB's - just
my view!

The Radiac 2000 Mark-1 runs off the 240V supply line but I have also included
the provision for external power. I included this feature so that I could take
the unit into the field seeking specimens of Uraninite and Torbernite in the
Adelaide Hills, the Mounty Lofty Ranges and the Flinders Ranges, which are
within driving distance from my home in South Australia. High grade Uraninite
and Torbernite specimens are very common in South Australia.

The unit also has a TTL out should I decide to connect it to my PC. I also
included an "auxiliary output" which runs off the ICM7555 chip just in case you
I decided to do some real GM Ghetto blasting by connecting the output to a
150Watt audio amp unit. The only tuning involves tweaking the LM393 circuit
using the 1M precision resistor so you get a "good" digital output to feed Pin-6
of the PIC16F628A. If you would like just an analogue GM you can exclude all
circuits except for the LV supply, HV supply and the ICM7555 units. This would
make a neat and portable analogue GM, and if presented in SMD format might make a very nice "flashlight" style GM counter.

Construction Manual

Humble Beginnings