We make a prefix - Geiger counter to the iPhone in 2 hours

UPD: Who has already read the post - please go and take part in the survey. Thank you very much!

About a year and a half ago, on several network resources, including those in the Habré, they began to promote the “Do-ra” project - an iPhone prefix that allows you to measure background radiation and do a lot of tasty things based on information received from a Geiger counter. Articles in the project news mention several multi-million grants allocated for the development of the instrument by the Skolkovo Foundation. The months went by, the “Do-ra” was still not working, the buyers were waiting, the competitors were not asleep. Is “Do-ra” so complicated, how it is painted and how to assemble a ten times more sensitive analogue from a scrap of a couple of hours from the parts at hand I will tell those who click on

')
So let's get started. More recently, I learned about the excellent (and also free!) Program GeigerBot, which processes incoming pulses from an ionizing radiation detector to an iPhone or iPad microphone input and has a nice feature: with a certain combination of settings, a 20 kHz sinusoidal signal is played through the headphone output. The combination of settings required for this is as follows: in ClickifyLab, all controls should be at the maximum, Echo Filter is enabled, and the Clickify function itself is turned off. Having done the appropriate settings, I was convinced with the help of a 3.5-mm plug and an oscilloscope that the signal actually appears and its span from peak to peak at maximum volume is about 1.3 volts. At this moment, there is no doubt that in an hour this signal will be used after a small transformation to power the Geiger counter, the pulses from which will be sent to the microphone input.
The counter was taken popular - SBM-20. To supply it you need 400 volts DC, you can get them in a standard way using a transformer having a high transformation ratio and a rectifier. A very high transformation ratio in transformers that supply cold cathode fluorescent lamps in the backlight of monitors. I turned up the backlight from the already-not-remember-what, containing the transformer SGE2687-1 (any suitable one, hundreds of types) with a transformation ratio of about 150. A little, but I did not have another, and the lack of voltage was filled with diode doublers. We take layoutka and start to collect the scheme.



The scheme turned out to be very simple: a transformer, two voltage doublers, a 390 volt varistor as a zener diode and a transistor to increase the duration of the pulses coming from the Geiger counter to the values ​​that are digestible for the iPhone's audio ADC. With proper parts and proper installation, it will begin to work immediately, the ratings of most parts can be changed within very wide limits without affecting the performance of the entire circuit. Insert the connector into the iPhone and run the application GeigerBot. Accurately high-resistance (not less than 100 MOhm) voltmeter or tester with additional resistance control the voltage across the varistor, it should be about 400 volts. Make sure that the type of the SBM-20 counter is selected in the GeigerBot settings and observe the number of recorded pulses. With a natural radiation background (0.1–0.15 µSv / h), the pulses will follow at an average speed of 20–30 per minute. With a large cable length from the connector to the circuit, the mutual influence of a relatively powerful 20 kHz output signal on the microphone input is possible, this can manifest itself in the form of a huge pulse recording rate of several thousand per second. To reduce this effect, two separate earth wires are used - for the supply and signal circuits. In case of such problems in the settings of GeigerBot it is necessary to increase the trigger threshold by the amplitude of the pulses (Settings - Geiger Counter - Custom GM tube - I / O Settings - Volume threshold - put 10,000 or so).
Here is a small video showing the operation of the device.



At the twenty-fifth second, the counter’s reaction to a saltcellar, made in the United States in the 1940s and covered with uranium glaze, is shown. At 35th, the pulse shape at the microphone input of the iPhone is shown.
That's all, that is, almost everything. In order to give our detector set-top box a finished look, we take a small piece of a suitable tube, shove everything that we have soldered into it, not forgetting to insulate parts of the circuit from each other and seal it at the ends with hot melt glue. Now everything, you can go to Pripyat: forewarned - forearmed.

Thanks for attention. Good luck to everyone in technical creativity and good environmental conditions!