Required Parts

The DIY Particle Detector comes in two variants.
The circuit board is the same for both, but the diodes and few resistor/capacitor values differ (D1-4,R3-5,R8,C4,C6,C9).

electron-detector - easier to build and operate for beginners, more sensitive to radioactivity than the alpha-spectrometer
- using 4 very low-cost BPW34F diodes as sensor and 21 other parts
- get parts & circuit board easier via kitspace.org or buy a complete kit
- parts overview & assembly guide PDF, German version
alpha-spectrometer - measures the characteristic energy of alpha particles (as well as detecting electrons)
- using 1 rather expensive BPX61 diode as sensor and 23 other parts
- get parts & circuit board easier via kitspace.org
- parts overview & assembly guide PDF
chose a suitable metal enclosure
minimum size housing the circuit board, batterie, switch and connector:
- 8 x 4.5 x 3 cm³ (9V battery upright)
  or
- 8 x 5.5 x 2 cm³ (9V battery flat)
few centimeters of flexible electrical wire to connect the signal output connector and on/off switch
the right cable, connecting the signal output with an oscilloscope or computer/smartphone/tablet
a 9 V battery
depending on the enclosure, addititional screws for fixing the detector inside the enclosure
- M3 distance bolts or 'PCB standoff'/hex spacers and a pair of corresponding M3 nuts and screws is recommended (made from metal instead of plastic)

Both variants of the detector require the same circuit board, but with different sets of electronic parts, the schematic drawing features both sets of parts in an overview.

Tips for ordering parts

Please use the two kitspace links above to find the right order codes for each variant from several different electronic part suppliers. There are no additional costs if you use its '1-click BOM' functionality, it merely copies the right amount of parts and their order codes into the respective shopping carts of supported suppliers. www.kitspace.org is community-run and intends to simplify the uptake and distribution of open hardware projects.

Unfortunately, not every electronic part supplier ships to private individuals in all countries. Mouser and Digikey are currently the more universal ones from the suppliers supported on kitspace. Both offer free shipping if a minimum threshold of ~50 USD/EUR is reached.

If you want to order as a private person, please check first which of the listed supplier supports this in your country. Then create your own account at the supplier's website, log in with your account and finally use one of the two kitspace project links (see above) to populate your shopping cart with the correct order codes for all required parts. Please open a new question in Discussions if you have problems with certain parts.

Required Tools

solder iron
solder wire
sharp pliers (preferably of the "side cutting" or "electronic" type)
small screwdriver
for creating holes in the metal case:
- either hole punchers and a hammer: 2, 5 & 9 mm diameter, for candy tin boxes
  (punching tools require smaller diameters than the final hole size)
- or a drilling machine: 3, 6 & 10 mm drill size, for thick-walled metal enclosures
either a hardware oscilloscope or a software oscilloscope/python scripts and a soundcard/headset input together with a computer/smartphone/tablet

Optional tools, but handy:

tweezers
a simple multimeter for measuring resistance (useful for finding problems and distinguishing the resistor values)

Build Instructions

Before you start soldering, make up your mind about how and where you want to mount the detector inside the metal case (please consider all the remarks on that page!).

If the enclosure is quite small, you may want to put the large capacitor C8 and/or the diodes D1-D4 on the opposite side as they are marked on the circuit board. For example, the detector is more sensitive if the diodes are very closely placed in front of a radiation window. C8 could be rather mounted on the opposite side of the board in such cases.

If the enclosure is rather large and radioactive objects will fit inside easily, the default position of all components on the board can be kept as marked.

Always use one of the two parts overview PDFs linked at the very top as an assembly guide. Solder the components as they are listed on those sheets, top-bottom, left column followed by the right column.
General note: The small capacitors and resistors can be mounted either way. Only C8, the diodes D1-D4 and U1 must be mounted exactly in the correct orientation since these are components with a specific polarity.

solder the resistors in the correct places as marked on the board, carefully checking for their color bands
cut all residual and protruding resistor leads off as close a possible to the board
solder the small (yellow) capacitors in the correct places as marked on the board
- C5 should be mounted as flat as possible if the selected enclosure is very small and if the battery will be directly on top of it
cut the residual and protruding capacitor leads off as close a possible to the board
- the leads of C5 must be cut as short as possible such that U1 can fit closely on top of them
solder the large capacitor C8 on that side of the board that fits better to the available space in your enclosure
- if unsure about the best position, keep 2-3 mm of free space between C8 and the board - this extra lead length provides an option to later bend C8 horizontally/flat if necessary
solder the diodes, 4 x BPW34F or 1 x modified BPX61, respecting their polarity (anode vs. cathode)
- the cathode pins must point to the board center, marked with the letter 'K' (see images below)
- Electron-detector: the BPW34F's cathode_pin is marked with a notch
- Alpha-Spectrometer: the BPX61's anode_pin marked with a notch, which must point away from the board
solder the black amplifier chip U1, respecting its polarity: pin 1 is marked with a circle on the board & chip
- double-check that the pins from C5 are cut short enough and do not touch each other
check all solder points on the board for possible short circuits, cut them short/flat if required
- optionally measure the resistance on the +/- 9 V battery connector holes, it must be much higher than zero: 9 to 10 kilo Ohms
make sure the chosen enclosure has all the required holes in the correct size for (c.f. Required Tools)
- signal output connector (BNC or audio), check if it fits in place and mount it
- on/off switch, check if it fits in place and mount it
- optionally, create a radiation window in front of the diodes
solder the black ground wire of the 9 V battery clip into the hole labelled '-', next to '+9V' and C8
solder the red wire of the 9 V battery clip to the middle pin of the on/off switch
strip the insulation from 3 short pieces of electrical wire at the ends
solder one short piece of electrical wire between the on/off switch and the hole labelled '+9V' on the board
solder a pair of short pieces of electrical wire between the board and the signal output BNC connector
- solder two wires into the holes marked with 'signal' and '-' on the board
- solder the other end of the 'signal' wire to the BNC connector's inner pin
- solder the other end of the '-' wire to the outer part of the BNC connector, usually surrounded by an extra connection ring Alternatively, the '-' wire can be soldered directly on tin box walls next to the connector (does not work with aluminum cases).
- if an audio connector is used instead of the BNC connector, tip/sleeve should be connected respectively
check all wire connections for possible short circuits, correct them if required
- optionally measure the resistance on the +/- 9 V battery clip connector, it must change when switching on/off
fix the circuit board in place with screws, either via the two metalized board edges or via one to two of the 3 metalized holes
connect a full 9 V battery, place it inside the metal enclosure
close the lid of the enclosure
- light must not reach inside, even the tiniest holes and slits must be covered with sticky tape from the inside

Top sides of the electron-detector variant on the left, the alpha-spectrometer varaint on the right:

The central label 'K' between the diodes D1-D4 marks the position of the cathode pins.
('K' was derived from the Greek word 'kathodos' - it also looks like the electronic diode symbol)