Geiger counters are designed to measure nuclear radiation, which, in practice, would be more like background gamma radiation. On the other hand, it is not a bad idea to measure gamma radiation given that it also happens to be the radiation produced by nuclear or radiation spills, such that a sharp increase in background gamma radiation might actually be related to a nuclear spill instead (in which case you can panic scientifically, not just like a layman!) OR WHEN "TEHY" ARE SCANNING THE PLANET FROM OUTER SPACE TO DETECT NUCLEAR BOMBS, SON!!!!11

There are many Geiger counters out there that are functionally the same and they all rely on a tube, usually called a "scintillator", that measures the actual radiation before it is converted by the rest of the electronics. The tube or "scintillator" is an excitable element, sometimes filled with gas, other times even filled with fluid, that provides a small electrical current whenever a gamma ray (or any other radio-nucleotide when speaking about scintillators) passes through. The electrical impulse is then gauged in terms of duration and intensity and then converted according to the specifications of the scintillator into a true physical value that measures radiation.

One good example, is the MightyOhm Geiger Counter Kit:

which is a kit distributed as components, PCB and tube that must be assembled before it can be used. There are some other aftermarket variants, some fully assembled and some not, by Chinese sellers, and most of these are just as good as the others.

The major problem with these sensors is that the tube (or, the scintillator) that these sensors rely upon are not particularly rare, however these tubes are created on demand, mostly en-masse, in Russia or China, but the producer does not really know the exact specifications of the tubes and more than often the datasheet for a tube in particular does not exist. Realistically, the audience that Geiger counters are designed for, is good enough to tell which tube they have and how it is used such that sometimes datasheets were never really created, with the producer not expecting consumers to dabble with measuring nuclear radiation (which, is a fair gamble).

As the sensors split between "relative" and "absolute", Wizardry and Steamworks actually chose a Gravity sensor for the sensor cocktail due to the same concern that the measured value might not be accurate and by buying a branded Geiger counter, the values reported might actually represent some physical measure that could be corroborated by any other Geiger counter.

After setting it up, the Gravity Geiger counter reports values around the value, which is a good value, with the scale set up being from zero to "right next to Cernobyl" ($800CPM) but capable to reach much higher in the hundreds of thousands in the presence of an active radiating source.

CPMs or counts-per-minute is a measuring unit for radiation that can be further converted into Siverts or micro-Siverts if need be. In fact, the Gravity sensor provides two helper functions to do so but in reality the conversion is purely algebraic. This is also one of the cases where the actual value being reported will seem elusive to most people, well, unless they glow in the dark and can find the actual numeric value relatable. Nevertheless, the following table, also provided by Gravity, should make the scale in CPMs more relatable:

One other computationally-interesting feature that could be explored using the Geiger is to leverage the entropy of background (background, as in, from outer space) gamma radiation due to the incidence of a collision between gamma particles and the scintillator is deemed to be inheritently unpredictable or non-deterministic. With that being said, the entropy can then be used to, say, create a true random number generator (TRNG). Alternatively, the extra entropy could boost the overall entropy of Linux machines via Linux-RNGd, similar to how the Moonbase OneRNG device performs the same job but by relying on radio radiation. The purpose for that would be to avoid low-entropy cryptographic attacks, even though, there are dedicated devices that provide a better entropy source in case such high-level securization is needed.

The Geiger counter features a small switch that is by default set to "on" which will make the geiger counter emit a sound whenever a gamma particle or ray is sensed by the tube - that "beep" represents a random incident, and the the "sequence of beeps" would then be fed as a series of digital "1s" or digitized in a different way in order to be fed into an entropy pool.

Luckily for us, Gravity also provides their own library, which spares the need to mess with the actual calculations, such that the following code was sufficient to provide accurate values in our case:

#include <DFRobot_Geiger.h>
 
DFRobot_Geiger geiger(GEIGER_PIN_ANALOG);
 
void setup() {
    Serial.begin(9600);
 
    geiger.start();
}
 
void loop() {
    float cpm = geiger.getCPM();
    float svh = geiger.getnSvh();
    float suh = geiger.getuSvh();
 
    Serial.printf("CPM: %.1f, nSv/h: %f, uSv/h: %.1f\n", cpm, svh, suh);
 
    delay(1000);
}

Insufficient data has been collected to provide a graph. Ideally, the CPMs will end up plotted in order to be able to observe irregularities. For now, it seems that we pick up way more radiation during the day than during the night and that should more than likely be blamed on sun activity.