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 had a team hackathon from the 26th to 28th August to work on our
Analogue PCB, which carries the front end amplifier (an AD8014 per
channel) and the SiPM's (on the reverse side for close coupling to the
scintillator slab). The tests were successful and we'll shortly be
posting a version 2.1 with some changes to the resistors and a couple of
extra traces and pads to permit the addition of an LED to inject light
into the scintillator slab for testing and calibration. Head over to the
files section to download the schematics and layouts.
We have also ordered prototypes of our Main PCB (Version 2) which should
be delivered soon. Of course we'll be testing them and sharing the
results as soon as we have a couple assembled.
Finally, we've also been testing the overall performance of our timing
system. We're working through a 0.5 baseline at the moment (basically
testing the robustness of our server and data transmission scripts)
before doing a long baseline timing test in a few weeks time. For up to
the minute updates follow us on Facebook!
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
*Raspberry Pi Hat form factor compatible for easy integration with
*Data acquisition, representation and storage software stack written in
*Fully open source design, released under CERN Open Hardware License to
encourage widespread use and
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!