Diode and inductor. about esp32-geiger-counter

[grillbaer]

Hi, you may use any series of zener diodes that add up to a voltage drop of about 400 V, e.g. 4 times 100 V in series. There's no need for a special type. Their max power does not matter, since there will be almost no current through it. So simply take the smallest ones. These z-diodes' task is to cut of the generator when their total voltage drop (=the target voltage) is exceeded, which works by a small current starting to flow through them then.

Both z-diodes and fixed inductors should be available from almost any electronics parts retailer.

My favorite retailer in Germany has e.g. this inductor https://www.reichelt.de/festinduktivitaet-axial-hm50-ferrit-10-mh-bi-hm50-103klf-p245509.html?&trstct=pos_3&nbc=1 and these z diodes https://www.reichelt.de/zenerdiode-200-v-2-w-do-41-zy-200-dio-p219675.html?&trstct=pol_2&nbc=1.
I don't know in which part of the world you live, so perhaps you better look into the products of a local retailer, maybe rs electronics or digikey are there.