cosmic shower detector v2

The [MuonPi Project](http://muonpi.org) utilizes an inexpensive Raspberry Pi B+ plug-on module for particle and nuclear physics detectors aimed for measuring muons from atmospheric showers triggered by high energetic cosmic particles. The goal is to set up a distributed network of these detector stations in order to determine the energy, timing, and eventually the origin of the primary particles. To do so, the detected events are timestamped utilizing an on-board GNSS receiver with a precision in the nanosecond range to search for event coincidences between other detectors in the network off-line. The circuit comprises two inputs for typical input signals (PMTs, SiPMs etc.) with positive or negative pulses (negative input with mounted inverting amplifier U1) of few hundreds of mV amplitude and several tens of nanoseconds length. Each channel comprises adjustable threshold discriminators for fast timing and amplitude processing with a fast peak-detector (channel 1 only) for amplitude measurement with the on-board slow sampling ADC. Timestamping of the single channels or a logic coincidence thereof (XOR or AND) is achieved with the interrupt input of a U-Blox NEO-M8N GNSS module with few tens of nanoseconds precision. This version of the circuit utilizes a cheap commercial DC/DC upconverter (XL6009) as plug-in module for bias voltage generation for the SiPM photo sensors (available eg. from eBay). In contrast, version 1 comprises an on-board bias voltage generator with software-adjustable output voltage (0...40V) via DAC MCP4728. The newer version 3 includes both of these options. This version is the current working version. However, if you like to build and use this hardware, consider the more recent [Version 3](https://easyeda.com/hgzaunick/cosmic_shower_detector_v1-52b8a2536bb6468e9f48412a774951d0_copy_copy), instead. Status: V2.1 design is complete, PCB was produced and tested. Device is operational.