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Sunday, February 24, 2013

Propeller based geiger counter part2

For the last 6 days or so I've had my Propeller demo board connected to one of the Sparkfun Geiger counters (GC) right next to my laptop and have gotten rather fond of the random blink of lights from these two boards as a high energy gamma ray plows through the GM tube and lets me be aware of its presence.

The previous post on this topic just had a mere 6560 intervals used in the construction of an inter-event histogram but it was enough to demonstrate the probability distribution of the background radiation. Over the interim, GC2 data has continued to stream to the Teraterm program which has been patiently recording the time of the event and width of the GC2 output pulse. As noted in the previous posts, the clock "tick" is 2 microseconds in duration so we have a rather fine grained view of the temporal structure of the data.

This is the final graph that I'm going to produce with this setup before I dismantle it as I need the Prop demo board to test out parts of my ambulatory physiologic monitor (APM) and the Propeller debugger I'm trying out keeps telling me my USB connection to an older Propeller project board is flaky. Hence, time to move on and will archive the version of the code I used and make a portable Propeller based GC although will definitely include a serial output on the device so can set it up as a semi-sessile device to monitor radiation in various areas.


As one would expet with a stochastic variable, the averaging of 83756 inter-event intervals produces a far far closer fit to the exponential function that describes the data. I especially like the correlation coefficient of 0.99885 which is a value that one never sees in wetware systems -- only elementary physical processes have this good a fit to a model. The reader is advised to review the previous post to see how much scatter was present with 1/15 of the number of intervals.

Was pondering why I get so excited over a simple GC and a few Mb of numbers last week and it finally dawned on me. Here's my very own way to demonstrate fundamental aspects of physical reality in a manner that serves to convince one of the fundamental truth of a theory in a far stronger way than just reading about radioactive decay and the statistics of radiation in a physics textbook. I wired up all the components in my circuit, I've got a GC that's totally open source and I could easily duplicate it if I desired to from the components, I've written all of the code that goes into the Propeller chip and I've taken a huge file of random numbers and generated an excellent fit to an exponential curve from it. This correspondence between physical reality and the "reality" of mathematics is something to admire. e is an irrational number that has its origin in exponential processes just like pi is a relationship between the circumference and diameter of a circle. One gets a feeling for the reality of "e" when one looks at this graph, although it would take an infinite amount of time for the random data to average out so the two curves were cojoint and the stationarity of the background radiation would probably be disturbed by local supernovae thus ruining that beautiful single exponential.

The next step is to replace GC1, the first Sparkfun GC I bought with GC2 in the windoze based sampling circuit. This will establish once and for all whether the "ringing" in the GC1 interevent histogram plots is the product of GC1 or windoze. I can speculate all I want about the vagaries of windoze but, to actually prove my point, I need to swap GC's and rule out the possibility that GC1 alone is the cause. That's the way that science works. Easy research to do, start the sampling program, wait for 1-2 weeks and then analyze the data.

The Propeller based system has produced many random numbers and, taking the low bits of the clock timings will hopefully produce "random" numbers which are good enough to pass the test on one random number website I found but have to now look for in my virtual rats nest of files on my machines.

Posted by Boris Gimbarzevsky at 8:34 PM