Q&A
Many of you had problems with that
circuit in that there was too much
variation between the NE-2 lamps,
making it unusable or impossible to
calibrate the counter.
Well, I have done a little research
since then and think I have found a
better design that uses — of all things
— a peanut can. The “Cheap, but
Sensitive Radiation Detector” can be
found at www.techlib.com/science
/ ion.html The design is by Charles
Wenzel, whose designs I trust. Figure
9 shows the basic concept. His
commentary is self-explanatory, so I
won’t go into it here.
The second missing part of the
equation was a radiation source. I
found that on eBay under the guise of
a Coleman lantern mantle. One
mantel produces 1.5 mr/hr (about
750 counts per minute) and sells for
about $5.00. You can also find them
from time to time at K-Mart and
camping supply houses. Look for the
brand that says “Made in India.”
The radioactive ingredient in the
mantle is thorium-232. By itself,
thorium is only slightly radioactive,
emitting only alpha particles that are
easily blocked by a thin piece of
paper.
However, thorium breaks down
into two parts: a small part — the
alpha radiation — and a larger part
called the decay product. The decay
products include radium and radon,
which emit alpha and beta particles
and gamma rays.
In fact, the longer thorium stands
(half-life is 14 billion years), the
more radioactive it gets — but that’s
another story.
Frequency
MHz
Number of
Turns
Tap at Turn
No.
Wire AWG
Coil
Diameter
Winding
Length
1. 8-3. 8
82
12
#26
1 1/4
1 9/16
3. 6-7. 3
29
5
#26
1 1/4
9/16
7. 3-14. 4
18
3
#22
1
3/4
14. 4-32
7
2
#22
1
1/2
29-64
3 1/2
3/4
#18
1
3/4
Table 1. Dip meter coil data.
Figure 9
A. Controlling the speed of an AC
motor is fairly simple. It’s done all
the time in hand drills, but what
you’re trying to control is a flow of
water, which has a lot of latency —
resistance to change in flow. No
matter how hard you try, the fountainhead won’t follow the fast-moving
audio. The controller needs a low
frequency filter to turn sporadic
into rhythmic. Here’s what I’d do
(Figure 10).
In this circuit, I’ve used the
control voltage input (pin 5) of a 555
timer to PWM (pulse width modulate)
the speed of the motor. With this
design, the motor is never completely
off — for good reason. Starting a
water flow from a stall takes a lot
longer than revving it up from a
trickle, making your fountain slightly
more responsive. It also takes care of
the low frequency filter I mentioned
earlier by using the inertia of the
Figure 10
+12V
115VAC
Hot
Three Coins in a
Fountain
Q. I want to hook up one or more
submersible fountain pumps
(typically 115 VAC, 0.8 A) to a circuit
that will vary the flow of water in
concert with the input from a sound
source. Should the circuit change the
voltage or current?
33k 8 4
7
555
Pump Motor
3 1k
MOC3010
180
1.2k
33k
6
2
0.2
TRIAC
+
5uF
15
115VAC
Neutral
Bob Slusher
via Internet
Audio In
Fountain Pump
JANUARY 2005
19