In Excel, I plot the count rate over time. Figure 8 is
an example of the count rate measured over a
period of six hours while monitoring Maxwell in his
cat tree apartment.
From my years of experience in startups and
product development programs, I’ve embraced the
motto, “Fail often and fail early.” This means I want
to design and build a prototype with the best
practices I can think of, but get it done quickly.
Then, I can use the prototype to test my approach. I
want to use my prototype to help me find the things
I could not anticipate, so the next versions get better
When I build Arduino circuits, I always start out
building them on a solderless breadboard. It takes
minutes to put something together and test out. Figure 9
is the prototype Geiger counter that I put together in
about three hours. It is so much quicker than designing a
circuit board, sending it out to get made, and assembling
it. When I have a final stable design and may want to
make multiple units, I will design a board at that time.
The downside to using a solderless breadboard is that
it may have more noise and not as good signal integrity as
a multi-layer circuit board. This is one reason I mount my
solderless breadboards on a copper base connected to
ground. I keep wires short and route signal lines close to
the copper base, and pay attention to all signal return
paths. In other projects, I’ve been able to keep voltage
noise levels from AC and RF pickup below 1 uV RMS.
My designs may not look pretty, but I can construct
them quickly, make changes on-the-fly, and optimize the
design in hours instead of weeks. They have surprisingly
When I turned on the voltage
to my Geiger counter, I
immediately began detecting pulses
when the applied voltage was
above 290V. I settled on 310V as
giving a steady rate of pulses, at
about 30-50 counts per minute.
This was the background I expected
to see, but was it really detecting radiation?
I needed a radiation source to test my Geiger counter
(remember my wife forbade me from ordering anything
that could potentially trigger a Homeland Security alert).
Turns out, I could buy one at Walmart.
There are two types of smoke alarms: photoelectric
based and ionization based. The ionization based smoke
detectors have a small piece of Americium-241. It is
radioactive, and emits an alpha particle and a very low
energy gamma particle. The gamma particle has an energy
of 59 keV which is in the range of dental x-rays. I had no
hope of detecting the alpha particle, as it would be
stopped by the metal wall of the Geiger tube. However, I
thought I might be able to detect the low energy gamma.
I bought an ionizing smoke detector for $7 and took it
apart. I found a piece of metal that looked like it could be
the ionizing source. I pulled this off the detector and
August 2017 37
■ FIGURE 10. Americium source pulled from a smoke detector and placed
on top of the Geiger tube.
■ FIGURE 9. Example of building a relatively
complex circuit using a solderless breadboard.
The entire circuit took about three hours to
design, build, debug, and optimize.