Een vriend stuurde mij op een chatkanaal de volgende pagina toe:

http://www.kempelektroniks.com/General/Tweaks.aspx

Ik dacht eerst bij een Nederlandstalige parodie op een doorgeschoten hifispecialist te zijn gekomen, maar naar enig gescroll kwam ik erachter dat alles op deze site gemeend was. Genoeg andere Nederlandse sites met “speciale”, enorm dure kabels welke, ondanks keiharde tegenargumenten uit de natuurkunde een enorme geluidsverbetering zouden moeten brengen.

Ik heb altijd vermaak gehad aan de hilarische, pretentieuze claims op vele audiofiele websites en aan hoe men terugkrabbelt als er door sceptici een zgn. dubbelblinde test van de gepromote produkten wordt voorgesteld.De site van Kemp Elektroniks, echter, presenteert een aantal voor mij nieuwe audiofiele “uitvindingen” waarbij ik geestelijk heen en weer werd getrokken tussen schaterlachen en alle vertrouwen in de mensheid verliezen.

Let op: Alleen verder lezen als je dit geestelijk aankan!

Hieronder een bloemlezing van een aantal produkten op de website:

De Audiodesk CD Sound Improver freest – onder een hoek van 36 graden – een randje af van uw CD, DVD of SACD. Het resultaat is een aanzienlijke verbetering in de weergave van uw muziek- en DVD-collectie. Na behandeling zal uw muziek boeiender en echter klinken.

Het duurde niet lang en de eerste pseudowetenschappelijke claims komen langs:

Empirisch is vastgesteld dat een hoek van 36 graden klankmatig optimaal is.

Echter in de praktijk is gebleken uit empirische metingen dat deze verontreinigd zijn met ferro (magnetische) materialen zoals ijzer, nikkel of kobalt waardoor zij de laserstraal kunnen afbuigen.

Empirisch? Ik geloof er geen snars van. Het zou me niks verbazen als het genoemde apparaat de onbalans in een CD juist verergert. Waarom zouden fabriekslijnen na decennia CD’s te hebben geperst nog met een dergelijk probleem zitten? De uitgebreide foutcorrectiemethodes in CD’s DVD’s, BD’s zorgen er sowieso al voor dat fouten door onbalansen en krassen worden geminimaliseerd. Sporen van ferrometalen welke laserlicht afbuigen? Serieus?

Voor optische media heeft Kemp een heel assortiment producten en tips. Men spreekt over het polijsten (niet eens zo’n gek idee) demagnetiseren (natuurkundig absoluut niet van toepassing op optische media), het elemineren van Argon van het produktieproces en als klapstuk het invriezen van CD’s!

De eigenaar van Kemp Elektroniks zegt in een interview op Hifi.nl het volgende:

Momenteel is er incidenteel nog wat discussie op fora die veelal worden bevolkt door mensen die mijn producten helemaal niet hebben geprobeerd en die soms niet eens over een goede installatie beschikken. Mijn echte klanten zijn over het algemeen zeer tevreden; ik heb zeker niet te klagen over belangstelling en waardering.

Juist,.we moeten dus eerst stervensdure spullen aanschaffen en over een “goede installatie” beschikken alvorens we een oordeel over de produkten van Kemp Elektroniks mogen vellen. Natuurlijk zijn de klanten tevreden, waarom zouden ze twijfels hebben in een aanschaf welke eigenlijk uit een geloofsovertuiging is gedaan?
Nergens op de site van Kemp Elektroniks worden claims onderbouwd, er wordt puur gegrossierd in aannames, tot absurditeiten als het toevoegen van Schumann frequenties aan netspanning toe!

Ik heb een mooie naam in gedachte voor dit alles: audiofiele homeopathie. Net zoals homeopathie werkt het niet, wordt er geen noemenswaardige schade aangericht en wordt er uiteindelijk alleen geld van goedgelovige mensen gescheiden.

Goede audio hoeft niet duur te zijn. Een goede versterker, degelijke speakers, voldoende dikke kabels er naar toe en een degelijke verbindingskabel naar je audiobron is alles wat je nodig hebt. Er zijn grotere gevaren voor audio dan goedkope spullen, zoals bijvoorbeeld hedendaagse producers welke mastering zien als een proces waarbij de naald continu bij de 0 dB moet blijf hangen.

Ik link als laatste nog voor de tweede keer in dit artikel de website welke al jaren de vloer aanveegt met audio onzin, het onovertroffen breem.nl .

Just some venting,

Why on earth is every interesting technical discussion forum on Yahoo Groups? I absolutely loathe its design. When requesting the main forum it presents you with unthreaded, ungrouped messages by date. To group messages by thread you have to click a link, and even then you have to click each message separately just to view it. It’s 2012 damnit, stupid threaded message boards should be a thing of the past!

It absolutely puzzles me why certain technical stuff ends up on Yahoo Groups. Especially hamradio and geiger counter stuff seems to end up on Yahoo Groups by default. Maybe people setting up these groups favor the usenet style interface because they are somewhat older than me and continue to use the annoying, threaded usenet-style interface because that is what they initially came in contact with when first using the net. Don’t get me started on search results…

(BTW, I found a modern message board focused on geiger counters and all kinds of radiation detection stuff, guess what, it’s only in Italian!)

Another annoyance of me lately has been expensive USB to TTL serial adapters. Most are based on the well known FTDI chip which is used on Arduino boards. Simple adapters using this chip have prices ranging in the €/$10-25 range, just for a simple device presenting a serial port to the host operating system and outputting TTL levels.
I guess the CEO of FTDI gets a nice bonus each year, selling loads of these chips for $3 when they likely cost pennies to make.

I’m still looking into a decent alternative, €15 TTL adapters suck!

English summary below

Via Ebay wat eitjes van Triops cancriformis besteld, de europese ondersoort. Ik heb eerder deze soort proberen te kweken maar de eitjes kwamen niet uit. Nu dus een nieuwe poging en er is leven in mijn kweekbakje. Eitjes lijken wat langzamer uit te komen en ook de ontwikkeling van de larven verloopt minder snel dan bij T. longicaudatus. Nu is het wachten op verdere ontwikkeling en hopelijk veel eitjes, want veel leek er niet tussen het zand te zitten…

On Ebay I scored some Triops cancriformis eggs, of the European subspecies. I tried breeding this species earlier but it failed for some reason. So, I tried again and now there is life in the hatching tank. Eggs seem to hatch somewhat slower than T. longicaudatus and development also seems slower. Now it’s waiting for further growth and hopefully harvesting of some eggs as the package I received didn’t seem to contain that many eggs.

In the picture you can see the HV generator on the top of the board, on the lower left the Arduino standalone parts along with a MAX232 as a level converter for easy serial hookup and on the right two tubes connected in parallel, a SI-29BG (beta and gamma) and a SI-12B for added alpha sensivity. Also shown are the USB>Serial adapter and a separate USB connector to provide 5V to the board.

I have had it running for some weeks with a Russian SI-29BG hard beta and gamma tube. These are nice, very sturdy tubes to experiment with. They easily detect natural background radiation and K-40 from a bag of Potassium Chloride.As I already explained I have connected two tubes in parallel. There wasn’t that much variation in background radiation, (see below) even after heavy rainfall so I am now going to watch whether alpha sensivity makes any difference.

Also, the SI-12B is kind of useless on its own, it is not very sensitive to beta and gamma but is able to detect alpha quite well due to its mica window.

Scripting

I have also changed my scripting on both Linux and Arduino to make everything easier to test and make it fail gracefully when the counter stops functioning for some reason. It also now works in Cacti with a GAUGE type of data, not a counter. This prevents spikes when the counter is reset or temporarily disconnected or offline. The script is as follows:

#!/bin/bash
# serial gmcounter update & log script
LOGFILE=/var/log/gmcount.log

function getcounts {
# display last 5 minute counts
# check if log was updated within 6 minutes
if [ `find $LOGFILE -mmin -6` ]
then
# print last 5 minute count
tail -n 1 $LOGFILE | awk {' print $5'}
else
echo "Error - logfile too old"
fi
}

function log {
# read counts from serial and write to logfile
read LINE < /dev/ttyUSB0
echo $(date) >> $LOGFILE
echo $LINE >> $LOGFILE
}

# check arguments and display or log data
if [ "$1" = "" ]
then
echo 'Use "getcounts" to display counts or "log" to log counts'
fi

if [ "$1" = "getcounts" ]
then
getcounts
fi

if [ "$1" = "log" ]
then
log
fi

I have put everything in one script and created functions to log the counts over  the last 5 minutes or display the last logged 5 minute count. If the logfile wasn’t updated properly it will return an error, causing Cacti to not record a value and show the error in its logfile. The script is connected to SNMP as described in my original article.

The Arduino script is as follows:

unsigned long counts = 0;
unsigned long fivemcount = 0;
long timer = 0;
long fivemtimer = 0;

void setup() {
Serial.begin(9600);
Serial.println("serial gm counter v1.0 starting...");
attachInterrupt(1, counter, FALLING);

}

void loop(){

if (millis() - fivemtimer > 300000){
 fivemcount = counts;
 counts = 0;
 fivemtimer = millis();
}
 if (millis() - timer > 10000){
 Serial.print("counts, cur: ");
 Serial.print(counts);
 Serial.print(" total: ");
 if (fivemcount == 0){
 Serial.println("n/a");
 }
 else {
 Serial.println(fivemcount);
 }
 timer = millis();
 }

}

void counter()
{
 counts++;
 tone(8,5000,1);
}

Basically, it counts the pulses, outputs the last five minute count every 10 seconds using the serial port and clears the counter after 5 minutes preventing any overflows of the unsigned long value (very unlikely). It also gives a very short tone with each interrupt which results in a little clicking sound. The random clicking helps me get to sleep quicker .

BTW, the current graph can be found here.

(picture: “Geiger Tube” by “dh” on Flickr, showing Russian SBM-20 hard beta and gamma GM tube)

On the internet there lots of DIY people showing off their homebuilt Geiger counter circuits, complete with microprocessors and LCD’s calculating and displaying count rates and often the dose rate in microsieverts/roentgen per hour.

The last thing surely makes a project look more impressive with the floating point number with a weird unit that most people are unfamiliar with. It’s not a big deal with DIY setups but there are lots of mentions of sending projects to Japan to help people over there “measure” contamination.

I would like to explain something I think is overlooked when implementing these projects:

You cannot convert counts per minute accurately to sieverts or roentgen per hour

If you look up information of a tube it will often specify how sensitive it is to gamma radiation of a certain isotope. For example, the specification of the widely used LND712 end window tube reads:

Gamma sensitivity:  18 counts per second = 1 mR/hr (Co60)

The tube is calibrated against a known gamma source, and the counts per minute to R/hr is only valid for gamma radiation emitted by Co-60.

In real life,  all kinds of radiation of different isotopes cause GM tube discharges. A GM tube does not give information about the particle/ray energy, it only indicates that something was able to ionize the gas in the tube. It doesn´t matter whether the tube detected a high energy secondary cosmic ray, or some weak beta particle just being able to penetrate the tube, it will give the same loud click.

However, this does not mean GM tubes are useless. They will detect most beta and gamma radiation and alphas (pancake, end window tubes) so most of the time they will give you information about whether something is radioactive or not, and how radioactive,  relative to the background. For example. I was able to measure that a porcelain mug I have is very slightly above background.

There are also other purposes for geiger counters in experiments. If you make an array of tubes and connect them to a microcontroller you can actually count particles that come from a certain direction, from space for example. It should also be possible to detect radon daughters decaying by pushing air through a filter and measure the radioactivity of the filter afterwards.

So, even with a  `simple` geiger muller tube you can perform interesting experiments.

Disclaimer: I am not a scientist. When you want to accurately measure radiation for some official purpose, consult a nuclear physicist.

Well, you could say that’s the free market in action. But it wouldn’t surprise me if prices are driven up by people not actually needing geiger counters but buying them anyway out of fear while they are not likely to experience any effects of the disaster.

Today I saw something much worse, some German on Ebay trying to sell a “geiger counter” which actually is a high range survey meter, a CDV715 according to the picture.

This person is even recommending this device to Japanese people. I would say that is a very bad recommendation because:

• this meter is high range, if the needle moves you are likely in the exclusion zone around the reactors where one shouldn’t be anyway.
• it will not measure smaller amounts of radiation, you cannot use it to check whether food or water has been contaminated or not, or compare contamination levels.
• it will mostly detect gamma radiation, so it won’t properly detect the beta radiation coming from the Iodine-131 release from the reactors which is something you really want to be able to measure.

It kind of sickens me that there are people trying to make money of this disaster while thousands of Japanese died and more are homeless, and have to cope with possible effects of fallout from the leaking reactors.

Finally, €199 is way overpriced for a survey meter, I bought a German made one for a mere €10. An original Civil Defense CDV715 should cost €100 at most.

It’s also possible to use cheaper, easier to find tubes with the CDV-700.  I found the following post from radio amateur K0FF on the “Geiger Counter Enthousiasts”  group on Yahoo groups. It describes a simple circuit to adapt tubes of varying voltage to the CDV-700. I built one, and it works!

I created a schematic to help people build this very handy circuit:

Parts:

R1 = 3.3 megaohms resistor 0.25 watts
R2= 1.8 megaohms resistor 0.25 watts
C1 = 10 nanofarad capacitor, rated 2 kilovolts
D1 – D3 = any number of zener diodes, the values added together  should be the desired voltage to regulate to

You can build this circuit in any way you want, keep in mind that there is high voltage involved, make sure that everything is properly insulated and that bare conductors are not closer to eachother than 2mm to prevent any arcing.

This circuit is basically a voltage regulator such as a 7805 built with discrete components and for higher voltages. To regulate to 500V for example, I used one 200V and two 150 zener diodes. 500V is a common voltage used by GM tubes.

With this circuit you are no longer limited to the more rare 900V tubes and you can connect all kinds of tubes to the CDV-700.  Keep in mind, however, that the CDV-700 may no longer display correct measurements in milliRöntgens per hour since the scale is calibrated for use with the 6993 tube.

I have always had an above average interest in radioactivity.  It’s a subject with political, sociological and scientific aspects. I have been mostly interested in the scientific part, but I also closely follow any news and other developments. With the earthquake in Japan and the following nuclear disaster the discussion about nuclear energy has  been fired up after being quite silent for years. In the Netherlands there was talk about building a new reactor next to the existing plant in Borssele. Well, I guess it will be a bit harder now to get support for this plan…

To be honest, watching the developments with the damaged reactors in Japan got me thinking again. Is nuclear energy a proper way of generating electricity? Sure,  for the immediate surroundings it is very clean. There are virtually no CO2 emissions and with proper shielding and maintenance you’ll need some pretty advanced equipment to measure any radioactivity coming from a reactor. Still, uranium mining is not very nice for the environment and there is no clear solution for storage of waste. And, if a reactor malfunctions there is the possibility of widespread contamination as currently seen in Japan. So, while I am not against nuclear energy my support for it has weakened somewhat.

Anyway, enough rambling, how to monitor radiation with your computer!

Update 18/4: Guess I am not the only one doing some monitoring: http://radgoes.blogspot.com

Geiger counter setup

I earlier built a geiger counter using the following circuit: http://letsmakerobots.com/node/18220 It’s an easy circuit because apart from high voltage capacitors and diodes most parts are fairly standard. The circuit has a 555 pulse shaper that converts the pulses from the tube into nice 0-5V signals. It’s also adjustable, not completely in the way I wanted, but by using the variable resistor and tapping into the end or the middle of the high voltage cascade I can get various voltages for different tubes. Most tubes will run at 400-500 volts.

I acquired tubes by buying an old German FH40T counter. It didn’t work properly anymore so I disassembled it for the parts, mainly the three tubes that come with it. The €40 it cost me is a nice deal even if you only get the tubes which can cost up to €23 separately. It comes with 2 low range (1R/hr)  tubes and one high range tube (50R/hr). The high range tube is of course less interesting but still a working tube for testing purposes. The sensitive tubes have the part number FH76V. Actually, according to the CDV-700 Club on Yahoo they are repackaged LND713 tubes. Specifications can be found here.

To connect the tubes to the circuit I had to get +500V out of it. At the end of the cascade the voltage was too high so I tapped into the middle of the high voltage cascade and with R5 and a high voltage adapter for my DMM I adjusted the supply to the correct voltage. To measure HV properly with your DMM you can build a HV probe cheaply using the following circuit.

By the way, watch out with high voltages. Even if the circuit is off, capacitors will retain charge, so discharge capacitors by shorting them before working on the circuit!

The circuit didn’t trigger the 555 properly so I made some modifications. I soldered a 50K potmeter over R12 to adjust the voltage of the pulsed fed into the 555. If everything is working, each pulse will be shaped and converted into nice pulses of 0V since the circuit inverts the signal from the tube. This seems to be a best practice for supplying pulses to a microcontroller because it provides a test signal, if there are no pulses the signal will be 5V, proving that the counter is actually on.

Arduino and Linux interfacing

If everything is working OK you can connect it to the Arduino. Since the circuit runs on 5V I was able to power it from the 5V supply of the Arduino itself.  Counts from pin 3 of the 555 are connected to pin 3 of  the Arduino, interrupt 1. The Arduino runs the following program:

long count = 0;
long timer = 0;

void setup() {
Serial.begin(9600);
attachInterrupt(1, counter, FALLING);

}

void loop() {
 lcd.setCursor(0,0);
 if (millis() - timer > 5000){
 Serial.println(count);    
 timer = millis();
 }

}

void counter()
{
 count++;
}

This simple program increments a counter each time the interrupt is triggered. Each 5 seconds it  prints this counter to the virtual serial port of the Arduino. If you monitor the serial port you should see the counter being printed each 5 seconds.

Note: this is a simple program, the long value count will overflow after 2147483647 counts. This number will be reached more quickly when measured radiation is higher. It shouldn’t be a big problem,  it will overflow after 510 years with my current measured background radiation.

Another note: To prevent the Arduino from resetting when the serial port is read, put a 10 microfarad capacator between the RESET and GND pins on the Arduino.

To log the value on my Linux server the following script waits for output from the serial port (will be autodetected when Arduino is connected) and logs the count with a timestamp, This script is run permanently by starting it with /usr/local/bin/getcountserial&

Script at /usr/local/bin/getcountserial

#!/bin/bash

while true
do
read LINE < /dev/ttyUSB0
echo $(date) >> /var/log/gmcount.log
echo $LINE >> /var/log/gmcount.log
done

To make interfacing with Cacti easy, I made another script that reads out the last line of the script:

Script at /usr/local/bin/getcount

#!/bin/bash

value=$(tail -1 /var/log/gmcount.log)

echo $value

This script is coupled to SNMP by adding the following line to /etc/snmp/snmpd.conf:

extend .1.3.6.1.4.1.2021.2000.4 gmc /usr/local/bin/getcounts

When this OID is read by snmpwalk, you will get the following output (rest of output snipped) :

UCD-SNMP-MIB::ucdavis.2000.4.4.1.2.3.103.109.99.1 = STRING: "32129"

Again, as in my Cacti temperature monitoring setup, use the most unique OID to get the value.

If the counts are properly registered, the rest is quite simple. Create a graph of a single OID, an instruction can be found here. There is a small change. The graph assumes data is per second, while the counts are measured over 5 minutes and need to be expressed in CPM, counts per minute. To get proper values I did the following: I duplicated the Generic OID template and named it CPM – Counts per Minute. I created a CDEF to convert the values from counts per second to CPM. I then coupled this CDEF to all the graph elements in the graph template.  I also added a comment to roughly convert CPM to microSieverts per hour.

You can find the live graph here: http://ruthenium.dyndns.org/graphs/graph_61.html

Final note: This is a crude setup and after completing it discovered it needs some tuning. It can be made more robust by getting the Arduino put out the actual measured CPM instead of the counts. That way the server still gets proper values even when it is restarted. When the Arduino is reset the counter will be reset to zero and Cacti will record a nice “radiation spike”  because it will see a large difference between the last recorded count and the zero value.

Op het moment ben ik wat aan het experimenteren om een bak met Triops wat represenatiever te maken met de dingen die je normaliter in aquaria voor vissen ziet. Ik heb grind gebruikt om waterplanten goed te kunnen laten wortelen, en een stuk kienhout op de bodem gelegd.

Grind is niet bijzonder geschikt voor Triops heb ik gemerkt. Ze hebben niet voldoende kracht om in fijn grind te graven. Daarom heb ik voorin de bak een gedeelte van het grind weggeheveld en het vervangen door zand. Zo hoop ik dat de planten goed kunnen groeien en de Triops goed kunnen graven om eitjes te leggen. Als het goed is zouden de eitjes zich voorin de bak moeten concentreren aangezien ze alleen daar goed kunnen graven.

T. cancriformis

Ik heb bij een Duitse postorder de soorten Triops cancriformis en T. australiensis besteld om daar eens mee aan de gang te gaan. Vooral T. cancriformis lijkt me erg interessant aangezien deze soort ook in Nederland voorkomt. Deze soort schijnt wel een wat lagere temperatuur nodig te hebben en groeien in een ander tempo dus waarschijnlijk zijn ze niet samen te houden met T. longicaudatus. Het is ook de bedoeling om ze apart te houden, dan blijven de eitjes ook zoveel mogelijk apart.

T. australiensis

Tot slot nog een tweetal interessante links voor mensen die zich verder willen inlezen:

http://www.triopsguys.com/ (Engelstalige site, weblog opzet)

http://www.urzeitkrebse.at/ (Engels/Duits, over alle grote diertjes van de order Branchiopodia)

This article will try to explain how to monitor and graph temperatures remotely using Dallas Semiconductor DS18xx sensors, SNMP and Cacti. DS18xx sensors are relatively cheap, accurate and multiple sensors can be connected to a single bus.

This guide is based on Ubuntu, so YMMV on other Linux/Unix based systems and may need modification to work properly.

Interfacing and software

To directly read out DS18xx sensors you need the following things:

- a Linux server running the software package digitemp (available on various platforms) and net-snmp

- a serial to 1-wire adapter (DS9097 or build one yourself with the following schematic)

- an installation of cacti running on a remote or local server

Setting up the hardware of the 1-wire network is outside the scope of the article. You can find lots of  guides to cabling and building interfaces on Google.

Testing and reading out sensors

When everything is connected properly you can try to read out the sensors. Make sure digitemp is installed and enter the following command  (this command assumes your first serial port is /dev/ttyS0, for USB serial adapters try /dev/ttyUSB0)

digitemp_DS9097 -w -s /dev/ttyS0

Digitemp should search (walk, hence the “-w”) the network and find sensors if they are connected:

DigiTemp v3.5.0 Copyright 1996-2007 by Brian C. Lane
GNU Public License v2.0 - http://www.digitemp.com
Turning off all DS2409 Couplers
..
Devices on the Main LAN
10A67CF501080074 : DS1820/DS18S20/DS1920 Temperature Sensor
10DF7DF5010800B7 : DS1820/DS18S20/DS1920 Temperature Sensor

In the example above two DS18xx sensors are found. If no sensors are found, check your cabling and sensors. It is also best to run as root to make sure there are no permission issues.

To make digitemp remember the sensors you have to store the settings in a configuration file. You can do a walk and configuration using the following command:

digitemp_DS9097 -i -s /dev/ttyS0

It should report the connected devices and confirm that it wrote a configuration file:

DigiTemp v3.5.0 Copyright 1996-2007 by Brian C. Lane

GNU Public License v2.0 - http://www.digitemp.com

Turning off all DS2409 Couplers

..

Searching the 1-Wire LAN

10A67CF501080074 : DS1820/DS18S20/DS1920 Temperature Sensor

10DF7DF5010800B7 : DS1820/DS18S20/DS1920 Temperature Sensor

ROM #0 : 10A67CF501080074

ROM #1 : 10DF7DF5010800B7

Wrote .digitemprc

It is best to move the configuration file to a central location, for example I use /etc/digitemp/digitemp.conf.  If you have multiple sensors you might be confused which sensor is which.  A simple way to check which sensor you are measuring is to hold it in your hand and probe the sensor indexes using the following command:

digitemp_DS9097 -t 1 -c /etc/digitemp/digitemp.conf

In this example, the sensor with index “1″ is measured. In the configuration file, the unique adresses of the sensors are listed so you can look them up or change the index of a device.

Interfacing with SNMP

To make interfacing with SNMP easy I wrote a script that reads out a sensor based on the index number and returns the temperature:

#!/bin/bash
# digitemp readout script

CONFFILE=/etc/digitemp/digitemp.conf

digitemp_DS9097 -t $1 -c $CONFFILE  | awk {' print $7'}| tail -n 1

This script takes the index as an argument and returns the temperature for that sensor, with all the other info stripped off. The awk command only prints the 7th column and that is piped to tail to only display the line the temperature was displayed on.

To couple this script to SNMP you have to add the following lines to /etc/snmpd.conf:

extend .1.3.6.1.4.1.2021.2000.1 temp0 /usr/local/bin/checktemp 0
extend .1.3.6.1.4.1.2021.2000.2 temp1 /usr/local/bin/checktemp 1

Shown here are two scripts coupled to different SNMP OIDs, both returning the script output for one of the connected sensors. Make sure the SNMP daemon has sufficient rights to access the serial port! On my Ubuntu 10.04 system I had to add the user “snmp” to the group “dialout” in the /etc/group file.

To test the scripts coupled to the SNMP OIDs, read them out using snmpwalk:

snmpwalk -v1 -c public localhost .1.3.6.1.4.1.2021.2000.2

UCD-SNMP-MIB::ucdavis.2000.2.1.0 = INTEGER: 1

UCD-SNMP-MIB::ucdavis.2000.2.2.1.2.5.116.101.109.112.49 = STRING: "/usr/local/bin/checktemp"

UCD-SNMP-MIB::ucdavis.2000.2.2.1.3.5.116.101.109.112.49 = STRING: "1"

UCD-SNMP-MIB::ucdavis.2000.2.2.1.4.5.116.101.109.112.49 = ""

UCD-SNMP-MIB::ucdavis.2000.2.2.1.5.5.116.101.109.112.49 = INTEGER: 5

UCD-SNMP-MIB::ucdavis.2000.2.2.1.6.5.116.101.109.112.49 = INTEGER: 1

UCD-SNMP-MIB::ucdavis.2000.2.2.1.7.5.116.101.109.112.49 = INTEGER: 1

UCD-SNMP-MIB::ucdavis.2000.2.2.1.20.5.116.101.109.112.49 = INTEGER: 4

UCD-SNMP-MIB::ucdavis.2000.2.2.1.21.5.116.101.109.112.49 = INTEGER: 1

UCD-SNMP-MIB::ucdavis.2000.2.3.1.1.5.116.101.109.112.49 = STRING: "24.25"

UCD-SNMP-MIB::ucdavis.2000.2.3.1.2.5.116.101.109.112.49 = STRING: "24.25"

UCD-SNMP-MIB::ucdavis.2000.2.3.1.3.5.116.101.109.112.49 = INTEGER: 1

UCD-SNMP-MIB::ucdavis.2000.2.3.1.4.5.116.101.109.112.49 = INTEGER: 0

UCD-SNMP-MIB::ucdavis.2000.2.4.1.2.5.116.101.109.112.49.1 = STRING: "24.25"

End of MIB

For some reason the output of the script is displayed multiple times. I always use the most unique OID (in this case the last OID on the output) and it seems to work all the time, no problems whatsoever. If SNMP is running and accessible by either the localhost or a remote server running cacti, you can read out the temperature from Cacti.

Graphing the output in Cacti

To graph a single temperature in Cacti is quite simple. Generate a new data source using the SNMP -  Generic OID template, fill in the OID and Cacti will poll the data every 5 minutes. To graph the data source, create a graph using the SNMP – Generic OID graph template. Under Graph Item Fields you can select the data source containing the SNMP data. Save the settings (Cacti could ask for a min and max value, enter something between -20 and 100 ) and the temperature should now be graphed. You can find additional Cacti documentation on this subject here.