A portable, USB-connectable geiger counter that is simple to build from readily available components. It's based on the popular SBM-20 tube, I designed a very energy-efficient 400V supply, it will run for weeks from a single LiPo cell. The USB interface can be used to recharge the battery, upload firmware and configuration and read out measurements.
I will upload the complete documentation once it's done :)
I am interested in your energy-efficient 400V supply. Has it been posted anywhere, or would you be kind enough to mail me a circuit diagram?