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Kvarts DRSB-01 Geiger counter USB mod

The Kvarts DRSB-01

The Kvarts DRSB-01 (Кварц ДРСБ-01) is a simple consumer Geiger counter. It does not feature a display of any kind like most modern Geiger counters do, but instead each particle detected by the tube make a very characteristic "click". It was manufactured in the early 1990's and is not made any more, but you can still find it commonly on places like eBay. I got mine for about 15€ a few years ago, but unfortunately prices have skyrocketed recently after the events in Fukushima brought back the reality that is radioactivity into everyone's minds.

A Geiger counter measures only ionizing radiation. Furthermore, as this device uses a metal shielded tube, only relatively energetic particles will be detected, that is mostly gamma rays or high energy beta rays. Is is not calibrated, and thus does not give a Sievert dose rating, but it can show relative differences of radioactivity between the background radiation and a higher activity by a correspondingly higher click frequency.

Box front Box left side Box right side Front Back

The device has two LED indicators, a green one marked ФОН (background) indicating normal background radiation, and a red one marked ВНИМАНИЕ (attention) indicating a level warranting attention.

A look inside

Let's open it up.

The enclosure is hold by a single screw sealed in some wax. It looks like my unit has the serial number #003711 and was manufactured in week 6 of 1992 :

Disassembly

Inside the case is a single sided circuit board holding the high voltage power supply, a counter and a timebase. Standard Russian components are used. The К561ИЕ14 is the equivalent to the CD4029 (Presettable Binary/Decade Up/Down Counter), and the К561ЛЕ5 is equivalent to the CD4001 (Quad 2-Input NOR Gate)

Circuit front Circuit back

On the top is the Geiger–Müller tube itself, an SBM-20U in this case. Some other versions of the DRSB-01 contain other types of tubes, probably depending on availability. In this case the high voltage power supply will be modified. That's probably why R2 is soldered on little posts.

Schematic

To figure out how to modify the circuit a schematic is needed. I was able to find the schematic online, but unfortunately I could not find the source. Credit goes to the original authors :

Kvarts DRSB-01 (Кварц ДРСБ-01) schematic

The tube is charged with a potential of about 400V. When an ionizing particle strikes the tube, it briefly becomes conductive and a current passes through R4, creating a voltage across it. This voltage is amplified by Q2 and then is fed to the binary counter U2. The green LED is attached to output Q1, and the red LED is attached to output Q4. U1 is wired as an astable mutivibrator oscillating at about 1/2 Hz, and is connected to the preset enable input of U2. The preset is hard wired to all zeros, so the effect is that the U2 counter is reset twice a second. This means that to show a red "Attention" indicator, the counter must detect at least 8 particles per half second.

The mod

I want to make this device more useful by adding an USB port which will allow quantitative display of particle counts and long term logging of radioation levels. Due to space constraints inside the case I will use a mini USB port. I also need a microcontroller with USB support. The ATtiny44, which I already used in my USB NES Pad project, will do nicely. Type B mini-USB ports are not that easy to find, and I don't have one at hand, so an old multi memory card reader that barely ever worked will generously donate his own :

Component donor Donor board Voltage regulator

I also extract the AME8805 voltage regulator as well as the 12MHz quartz and a few filtering capacitors from the donor board.

Schematic

The mod schematic. The COUNT signal must be connected to the point between U2 pin 15, the collector of Q2, and R6. To be able to power the device from the USB port only, I added a 1N4004 diode in series with the 3.6V supply. This diode has a drop of about 0.6V, just perfect to provide 3.0V equivalent to the batteries. The 3 filtering capacitors are low ESR ceramic type. They can also be replaced by a 10uF electrolytic + 20nF MKT in parallel.

Schematic of the mod

The mod is mostly independent from the original circuit. It only takes its input from the clock signal on pin 15 of U2, and provides 3V to allow operation without batteries. Note that if you have batteries in your device when the USB port is plugged-in, the ON/OFF switch must remain in the OFF position. Otherwise current might flow into the batteries and they tend not to like it.

Now let's assemble the circuit in such a way as to make it fit in the little free space we have inside the enclosure :

Prototyping phase Dead bug style assembly (kinda)

The circuit in prototype phase and assembled dead bug style (kinda).

Source code and binaries

One of the worst pains of USB is the need for drivers (particularly under Windows). However there is one class that does not need a driver for any OS : the HID class. The USB designers seem to have had the simplicity of implementation and use in mind when writing this specification. May they live long and prosper. So I implemented the USB device as a standard HID device. Plug it in your computer, and tada! It is instantly recognized and useable. The devices identifies itself as an LED with a 16 bit counter attached. A bit strange, but it does not seem to pose any particular problem.

Unless you used the USBtinyISP way explained above, you'll need to burn specific fuses for the circuit to work : low 0xdf, high 0xdd, extended 0xff.

Results

Here's what the device looks like after the mod. The exterior aspect of the device is not damaged. The switch on the side is to turn off the speaker, no need to hear constant clicking when using the detector for long-term monitoring.

View of the USB port Finished product

Windows software

To test the operation of the mod, I made a small Windows software in Java. Accessing the USB port in Java proved to be a little tricky due to the complete lack of support for USB in the language, but thanks to the HID class and this blog post it was relatively easy :

View of the USB port

The dose values are the result of the multiplication of the detection count by a constant calibration factor that depends on the tube and the nature of the radiation. The SBM-20U tube datasheet gives calibration values for strontium 90 and cobalt 60. For this test I just used a random value.

I collected one hour worth of detection events, it might be interesting to perform some statistical analysis on this data. The potential as a random number generator is quite low however considering the low event rate.

Here is the source code for this software. It's a maven project, unzip and run 'mvn compile exec:java'.

Graphs

One of the main reasons I built this mod was to monitor ambient radiation levels and be able to notice if a giant radioactive cloud flies over the city. So here it is. For simplicity I decided to write a Munin plugin for this, since I already had the infrastructure in place and it is a perfect tool to draw nice graphs. Here is the script :

#!/bin/sh
 
if [ "$1" = "autoconf" ]; then
   echo yes
   exit 0
fi
 
if [ "$1" = "config" ]; then
   echo 'graph_title Geiger counter'
   echo 'graph_args --base 1000 -l 0 '
   echo 'graph_period minute'
   echo 'graph_vlabel Counts per minute'
   echo 'graph_category environment'
   echo 'graph_info Counts per minute'
   echo 'geiger.label counts'
   echo 'geiger.draw LINE2'
   echo 'geiger.type DERIVE'
   echo 'geiger.min 0'
   echo 'geiger.max 65535'
   exit 0
fi
 
event=/dev/input/by-id/usb-Bidouille.org_Kvarts_DRSB-01_USB-event-if00
od $event -t u2 --width=24 -N 24 | head -1 | awk '{printf "geiger.value " $12 "\n"}'

The device id is hardcoded, it's probably a bad idea since it might change between kernel versions or for any reason. Ideally the device name should be grep'ed from /proc/bus/input/devices. However it does work :

By day By week
By month By year

Well the graphs do actually show some pretty big variations; this is unexpected as the background radiation should be fairly constant. Actually I may have damaged the tube during testing by inadvertently applying about 700V instead of the recommended 400V. However some parts of the graph look suspiciously like exponential decay, so there may be more to this. If you have any explanation, please comment below.

Tweeting

Sorry, won't do ;-)


That's all folks.

Sources


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Comments

Comment left by Petr on 2012-12-10 10:52:25 :
V rot mne nogi.... 0_6
Comment left by Mikhail on 2011-05-25 19:12:46 :
06.92 manufacturing date means June 1992 (i.e. month 06 instead of week 06)
Comment left by Philippe on 2011-05-22 00:36:23 :
@Duder Exactly how many languages do you speak, Mr. Oh-so-courteous? I know four, including French and English. Hit the books, elevate yourself, and stop being such a pretentious a**.
Comment left by Radiationbiologist on 2011-05-17 08:42:29 :
Hello,
the background radiation is not constant and actually depends on the Radon in the air, which changes with the weather. You might want to check whether the big change around week 14-15 is due to weather changes. Also the background radiation in your house depends on your geographical position and the type of house. Very old stone houses often have a higher Radon emission than newer wood houses.

Best
Radiation biologist
Comment left by efisher on 2011-05-14 19:45:12 :
The gieger counter circuit is extremely inaccurate. The 4000 series cmos logic lower supply limit is 3 volts. Add to that an RC timebase which will fluctuate at this low a frequency (~2 hz). A low leakage cap for the timing would help. I would also add an inductor in series with the 3V supplying the hv supply and decoupling caps on the CMOS logic.
Comment left by Eaglesfire on 2011-05-14 00:46:47 :
time base your spikes in the graph to solar flares, will prob match up. Also, those types of tubes either work or don't work, yours works. Also check the input voltage/current, MUST be constant to get a constant reading.
Comment left by macona on 2011-05-13 21:07:59 :
You may have damaged the tube with the high voltage. You can always pick up a replacement on ebay. Also you might want to monitor tube voltage. You may be getting a large change as the batteries are used. There is nothing resembling voltage regulation there.

Even on very good counters you can barely tell fukushima happened.
Comment left by Tim on 2011-05-13 20:40:52 :
Maybe the variation in background radiation is due to fukushima? Im not sure where you are geographically.
Comment left by JackTheVendicator on 2011-05-13 19:51:18 :
Maybe the peaks and the instability are induced by dirty switching usb power?
Comment left by termm on 2011-05-13 19:33:16 :
@Duder, Thats because some of the articles of this web site are written in french.
The poster is french and so is the name of the site.
Anyways, I have to agree with you that when you read something you should post in the same language.
Comment left by duder on 2011-05-13 18:40:47 :
Someday, sometime, you Frenchies who obviously know English well enough to read a web page will also bother to comment in the same language as a courtesy to the rest of us...
Comment left by andre villard on 2011-05-09 18:40:22 :
ce serait assez étonnant que le tube n'ait pas supporté les 700V
à propos comment as-tu mesuré celà (les 700V) ?
sinon pas d'explication pour le moment sur le fait que le niveau de radioactivité n'est pas constant ...
il faudrait réfléchir aussi sur le fait de savoir pourquoi il y a des pics très étroits
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