Robert,

No problem getting in touch, that’s why we have an interest group.

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Yes, my detector uses tubes like the SBM-20, mine are actually CTC-5. I should have some pictures, but can’t find them just now. I changed my network attached storage box and have not moved things over yet, quite a task, something for Winter nights. I have attached a sketch which shows how I have 5 tubes arranged to produce a square active area about 75mm on each side. The tubes are diode gated together to produce just one output. I have two of these boards stacked and the outputs are taken via high speed comparators to an old fashioned fast logic based coincidence circuit. The coincidence window is only about 25ns long.

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The tubes are supplied from a stabilised 400v supply. I used parts from an electroluminescent backlight PSU PCB. Unfortunately these seem to have disappeared from eBay, but I am sure another suitable arrangement can be found. I do not use Beagle Bone boards for the recorder, I use a PIC 18F8722 based arrangement. I may have mentioned the Beagle Bone Black in passing. The boards are very good, but to be honest I have not built any personal projects using one. I built four into an X-Ray camera for a NASA sounding rocket, to store images from four CCD detectors, which is how I got familiar with them. As soon as I had proven that the image capture worked, the project was moved on for students to develop. Hopefully the OGRE sounding rocket X-Ray telescope will fly in 2024.

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Capturing data when using a hardware front end is not difficult. My hardware simply operates a set/reset latch when the GM tubes detect a particle, the computer gets an interrupt to say that the counter needs to be incremented and then the latch is reset. Of course there has to be some formatting of data and timestamping. I recorded the count every 10s and pack these samples into a frame that holds 120 counts. This limits the size of each frame to about 512 bytes, a convenient size for a medium size PIC processor with limited memory. It also suits the page size of an SD card using an SPI interface. For this project, storage on a 16GB SD card is effectively unlimited.

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I download the data and control the detector using the STARBASE command structure developed by myself and Laurence Newell. That project went nowhere, but the Staribus protocol I developed has been useful. I use it on my CRD, Magnetometer, VLF Rx and BBC H-Line telescope. All messages are of a similar form which makes development of a GUI’s very easy once you have one working. The protocol is also in use at synchrotrons at Diamond Light, Brookhaven and PSI in Switzerland. I developed a temperature controller for a camera with sensors working at cryogenic temperatures. The OGRE camera also has the same temp controller and its camera configuration also uses Staribus. So STARBASE was not a total failure.

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If I can hinder you in any way please let me know. Small Cosmic Ray detectors are not very dynamic, but I am interested in the very occasional odd events that I see. The more system there are out there working, the more likely it is that we will understand these events.

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Have you got the H-Line Rx working? I cannot use my system here at home, I am on a housing estate where the EMC wipes out everything. Sad…

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Regards

David Farn

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