Cosmic Pi - a low cost distributed cosmic ray detector, based on
Cosmic rays are everywhere, flying through the atmosphere, our bodies,
our computers, everything. Previously the detection and analysis of
Cosmic Rays was the exclusive domain of high energy physicists. We aim
to make the detection and analysis of cosmic rays accessible to
students, educators and ordinary people with an interest. The Cosmic Pi
started as an after work project at CERN and is available here under the
CERN OHL for all to build. It uses a specially designed detector
combined with the low cost hardware of the Raspberry Pi computer for
data storage and online analysis.
At the moment we're using the free version of
EagleCAD to develop our electronics and
all files available for download are in this format.
We've now completed assembly and distribution of our first 40 units (Version 1). However we have some issues with the signal/noise ratio. We're working on some changes to our Arudino firmware to attempt to fix this. We're also going to start development of a Version 2 to address the issues we've found on our Version 1. This will be starting in April.
Issue tracking is now turned on, if you have issues with the design you can track them here under the issues tab.
Known bugs with Version 1
The current mainline firmware has issues adjusting the voltage and thresholds applied to the SiPM detectors, leading to very high noise at the output. A significant part of this issue is due to a single HV supply for the biassing of both SiPM's, which will be addressed in Version 2. We are also working on delivery of a client to run on the PC (Linux) - for connection to our servers.
Technical Specification Prototype 1
*Low cost plastic scintillator detection medium
*SiPMT readout from scintillator
*On-board multi-stage analog front end
*Coincidence triggering with variable threshold
*2 channel, 12 bit ADC
*Integrated -72V DC power supply (Version 1)
*GPS for detector localisation and 300uS timing accuracy
*33 MHz event clock (Version 1)
*MEMS barometer for altitude and atmospheric pressure
*I2C Temperature & Relative Humidity sensor for calibration and Scintillator monitoring
*Raspberry Pi Hat form factor compatible for easy integration with Raspberry Pi
*Data acquisition, representation and storage software stack written in Python
*Fully open source design, released under CERN Open Hardware License to encourage widespread use and adoption
Known bugs with Prototype 1
Lots: Hard limit of 1 Hz for event rate due to timer implementation, Murata PSU isn't suitable for SiPMT as it's too noisy. The ADC's are not pipelined and we have issues getting the Raspberry Pi to respond fast enough via the interrupt using standard Raspian. Version 2 is going to have a different hardware architecture to avoid these flaws!