This detector uses a silicon photomultiplier (SiPM) instead of the usual photomultiplier tubes that are more common with these types of DIY projects. This means that the whole assembly is much smaller and also safer, because no high voltages are needed! Also in contrast to projects like theremino you don't strictly need a computer or even an external sound card -- everything is self-contained. You can do standalone measurements using only a USB power cable and save the spectra to the Pico's flash storage or connect to your PC via the Serial-over-USB connection.

Hardware design has been done with EasyEDA and all the needed files for you to import the project as well as the schematic can be found on GitHub. There is also a Gerber file available for you to go directly to the PCB manufacturing step.

The software aims to be as simple as possible to understand and maintain; to achieve this I decided to use an off-the-shelf microcontroller - the Raspberry Pi Pico. This board can be programmed with the Arduino IDE over micro-USB and is powerful (dual core, good ADC, plenty of memory, ...) enough for the purpose and also exceptionally cheap.

A much more detailed and up-to-date look can be found in the GitHub repository at https://github.com/OpenGammaProject/Open-Gamma-Detector...

Here are some of the most important key facts:

• Compact design: Total size 120 x 50 mm. Approx. 70 x 50 mm area for electronics and additional 50 x 50 mm to mount a scintillator.
• All-in-one: No external parts (e.g. sound card) required to record gamma spectra.
• Standalone spectra recordings on built-in flash.
• Easily programmable using drag-and-drop firmware files or the standard Arduino IDE.
• Low-voltage device: No HV needed like with photomultiplier tubes.
• Can use SiPMs in the voltage range of 27.5 V to 33.8 V.
• 4096 ADC channels with built-in 3 V voltage reference.
• Energy resolution of up to 7% @ 662 keV possible; highly dependent on your SiPM/scintillator assembly.
• Energy Mode: ~20 µs total dead time while measuring energy (default settings).
• Geiger Mode: <5 µs total dead time without energy measurements (default settings).
• Low power consumption: ~20 mA @ 5 V with default firmware at normal background.
• Built-in ticker (buzzer) for audible pulse count rate output.
• Additional broken-out power pins and I2C, SPI and UART headers for custom parts (e.g. display, µSD card, etc.).
• Simple OLED support out of the box (SSD1306 and SH110x).
• Built-in True Random Number Generator.

Link to GitHub repo: https://github.com/OpenGammaProject/Open-Gamma-Detector
Also on Hackaday: https://hackaday.io/project/185211-all-in-one-gamma-ray-spectrometer
Buy a detector board: https://www.tindie.com/products/28827/