Hints & Tips
• To view and change the board files and schematic,
go to www.expresspcb.com and download their free
CAD software. There is no obligation and you will not
be harassed by emails.
• Microchip provides free software for the
programming of their microprocessors. Go to www.
microchip.com for information.
• When using hour and day readings, until you get
60 minutes or 24 hours, the unit will show that it is
counting and will give the number of hours to go.
D5 is a zener that changes the voltage. The one
recommended is 270 volts. To get higher or lower
voltages, change this zener. To the left of the zener is
another set of pads. You can place zeners in series and
add their voltages. If using a second zener, make sure you
cut the small trace between the second set of pads.
Note: The generator cannot supply much current. An
ordinary 10 megohm voltmeter will pull the output voltage
quite low; a very high impedance voltmeter is needed to
directly measure the output voltage.
Here is a technique you can use. Take a 100 megohm
resistor and place it in series with the voltmeter probe.
If you have a 10 megohm meter, this will give a 1: 10
reduction. Measure the voltage from ground across the
cathode of the zener diode. Note the voltage on the
voltmeter and compare it to the voltage of the zener.
Perform a ratio. This will correct for the meter’s input
resistance, e.g., voltage of zener = 270 volts; voltage on
Now, measure the voltage on the cathode of D4 and
multiply it by the factor used. This will give you
(approximately) the correct voltage of the circuit.
If you use another tube besides the LND 712, check
its specifications for the voltage needed to drive the tube.
RECORDING USING WINDAQ
I normally record an event once per minute. Make
sure you are only using one recording channel. To record,
click “File” and then “Record.” Make up a file name that
you can remember. Once you name it, a window will pop
up and ask for the number of kilobytes. Make sure you
put enough in for 24 hours of recording. You can do this
by holding down OK, and observing the hours and
minutes. If this is not correct, move the arrow off of OK
and input more or less KB. Click OK when finished.
You can change the units by clicking on “Edit.”
Go to the engineering unit settings and make five volts
= 4096 counts.
When finished recording, click “File” and then
Perform a search with the name you stored the data
in. Click on it and the Windaq software should open.
Press F7; it may take a few seconds to load. Click on
“Maximum.” The display should have 24 hours of data
on one page.
The first Geiger counter I had was back in 1989 and
was an Aware Model RM- 60. They are still manufacturing
counters, but they start at about $180. They make a good
product, however. On their website ( www.aw-el.com),
they have a lot of information on Geiger counters,
including sites to experimentation. They also have
methods of measuring radon that can be applied to
Check out https://sites.google.com/site/diygeiger
counter/gm-tubes-supported for more information on
different Geiger tubes.
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