With its small size of only 10 x 2.5 cm this board features everything you need to get running with a simple scintillation counter. The SiPM power supply is built for any SiPM using 28 - 34 Volts. The output signal is fed into a comparator that outputs TTL pulses for every detected gamma-ray.
The Mini SiD is a stripped down and much smaller version of the Open Gamma Detector. It can be used with any input voltage from 3.2 - 5.5 Volts. The outputs include a raw pulse pin and a single TTL out that can be used for time-over-threshold applications!
By connecting the TTL "INT" pin to an interrupt pin of a microcontroller, you instantly have yourself a simple, but very powerful scintillation counter. It's as easy as that! Of course, you can always use the raw pulses from the "SIG" pin and connect it to a MCA to do some gamma spectroscopy.
Details
Here are some of the most important key facts:
Compact design: Total size 100 x 25 mm. 51 x 25 mm area for electronics and additional 49 x 25 mm to mount a small scintillator.
Input voltage: 3.2 V - 5.5 V.
Low-voltage device: No HV needed like with a photomultiplier tube.
SiPM voltage range from 27.5 V to 33.8 V.
Low power consumption: <5 mA @ 5 V in standard operation.
Adjustable gain for the SiPM pulses, also affects pulse decay time and therefore dead time.
TTL output for counting pulses or time-over-threshold applications.
Additional raw pulse output if you want to manipulate the signal or use it for spectroscopy.
Dead time only limited by the speed of the scintillator and the gain. Typically <10 µs.
Only needs an additional cheap microcontroller to, for example, build a simple scintillation counter.
Just updated the silk screen on the PCB one last time, because the OSHWA certificate was just issued and I added the mark. Like I said last time, there are no changes in the actual hardware, I only updated the mark on the PCB, that's it. Cheers!
Just did a quick rework of the 2x2 MicroFC SiPM array PCB, added the temperature compensation from the single PCB and cleaned up the layout in general. It's now 2x2cm in size and still keeps the easy solderability for the four SiPMs (results in a fill factor of ~40%), while also adding the ~21mV/K slope for the power supply.
Front side with only the four SiPMsBack side with all the other components
If you want to use it, just connect your power to the "VCC" pad, ground to "GND" and then the SiPM anodes to the Mini SiD. You can check the set voltage at the "C" pad on the PCB. If you don't want to use the extra circuitry, you can just solder your power straight to the "C" pad and not bother with the other circuitry. However, you'll still have to solder the low-pass filters for each SiPM, otherwise they won't work.
I finally came around to finish the PCB layout for the latest (and probably last honestly) hardware revision of the Mini SiD. In short, this is a small-ish quality-of-life update with some nice changes that should make it easier to use, while still not changing a whole lot fundamentally.
This is what the new PCB looks like, I still need to get the OSHWA certification for this again, so the files are not completely final, altough everything's functional. The files and all the additional info can be best found on GitHub: https://github.com/OpenGammaProject/Mini-SiD
Changes in this revision:
Switched from a 2-layer PCB to a 4-layer PCB for much better signal integrity.
Improved PCB layout and shielding in general.
Decreased length of the electronics section by 2 millimeters.
Slightly more filtering for the SiPM output voltage.
Consolidated all the diodes to use the same chip to reduce BOM clutter.
The pulse discriminator reference, input resistor and power supply feedback path all now use much tighter tolerance resistors with less temperature dependence. That way it's less susceptible to temperature changes.
The pulse discriminator range has been slightly decreased for easier setting the correct voltage.
I think these changes are a great way to expand upon the last version that already worked well enough to be usable. It also marks a great point to say this project is more or less completed. It's usable, it works great and IMO there is not much that can be changed anymore without some fundamental changes. So thanks to everyone for your support and posting your interest and suggestions. Feel free to continue doing so!
There will be one update when the OSHWA certifies the hardware again, so expect that in the next couple of days.
Hello there, this is just a very quick update on the state of the project since I haven't reached out to you in quite a long time. I've investigated some issues with the temperature dependency of the threshold and the gain. It's not a big issue, but it can be annoying if you use the board in an environment where the temperature can change over a much wider range than indoors. You can always increase the threshold a little bit above the needed voltage to have a small safety margin, so it won't affect you nearly as much.
These problems will be fixed with a slight change in parts and more optimized circuitry. I'm going to do one final updated revision of the board with these changes and maybe some other slight improvements that come to my mind. I'll update you once the work is done and the hardware is ready, so stay tuned!
On another note, the Mini SiD is sold out on Tindie, so thank you all for your interest in this project and the support. You can still get some of the Tiny MicroFC breakout boards if you want, the sale is still on until the end of september.
From September 1st to 30th there will be a site-wide sale (-10%) on my Tindie Store, including the Mini SiD, the Tiny MicroFC SiPM breakout board and the Open Gamma Detector. No limit on the number of uses or products!
Finally, the Tiny MicroFC SiPM breakout/carrier boards are now available on Tindie! I have added some volume discounts for the PCBs and purchase options together with the Mini SiD and Open Gamma Detector.
Thanks to all the feedback and demand from you guys for the SiPM carrier boards. It's been long overdue to add these to Tindie so that you can get the PCBs together with the detector electronics.
Just wanted to let you know that there are only 3 of the fully assembled Mini SiD boards left on Tindie. This is the final batch, after that there will be no new production run. So if you want to get your hands on one, this is the last chance.
Here is a new and updated revision of the MicroFC SiPM carrier board: It now has some extra circuitry for temperature gain compensation! The overall size of the PCB and the solder pads have not changed at all and the bias filtering is also still on there. In addition to that, you can also use it without any of the additional electronics on it too. Don't need temperature compensation or any of the filtering? Just leave out all the components on the back side and solder directly to the anode and cathode pads for the SiPM.
If you do want to use the compensation circuit, a new BOM, Gerber file and schematic have been uploaded to GitHub. Kitspace should update too in the next couple of days (hopefully). Here is a link to the repo: https://github.com/OpenGammaProject/MicroFC-SiPM-Carrier-Board
It works completely passively without any sort of user intervention. It's based on an NTC thermistor that sits on the back side of the PCB, which is a big plus for temperature accuracy since it's on the same board as the SiPM. It's also low-power enough so that there is no unnecessary self-heating of the PCB. Just be sure to increase the SiPM PSU voltage a little bit as the compensation circuit initially drops a couple of 100mV to increase the temperature range without any need for readjustment. And ideally, you'd want to set the correct voltage at around normal ambient temperature for the correct tracking range (e.g. ~29.5V @ 25C).
Most of the research and testing has been done by Sebastian D'Hyon, so big thanks to him.
Finally, here are some screenshots on what the new board looks like:
It's a mini SiD connected to a microcontroller that works like a voltage controlled oscillator with a buzzer! It'll change it's output tone frequency with the measured activity. There is a really cool video on GitHub (link above), that I can't really show you here, where he demonstrates the device packaged in a tube with a 3D printed handle. The samples he has collected here are pretty impressive, especially since he's got no problem detecting the rocks already from a couple of meters away.
Just released a new, extra small carrier board for the 6mm MicroFC SiPMs. It's only 10x10mm in size with the SiPM on the front side and all the solder pads + an optional RC low-pass filter on the back. Usability-wise it's exactly the same, but it's smaller! That makes it A LOT easier to use on small scintillator crystals.
This is an optional step if you're using the carrier boards. If you're not and just soldering wires directly to the SiPM or doing it otherwise, skip this part.
All the SMD parts, the pin header and the SiPM itself. Orient yourself with the schematic and BOM. You can solder the pin header or, even better, use small wires instead.
Optionally, you can also skip this part and use the raw SiPM on its own and try to solder some small wires directly to it. That's not recommended though, as this whole process is quite delicate.
2
Couple SiPM with scintillator
Center the SiPM on the scintillator crystal and put some silicon grease between the two parts to optimize the coupling (and minimize reflections)
3
Wrap scintillator assembly
Use black electrical insulation tape or similar non-transparent material to wrap the whole assemby, but watch out for the connector or cables, of course. This will reduce light passing to the SiPM to an absolute minimum, otherwise it won't work properly. You should use multiple layers of tape just to be sure.
NuclearPhoenix
sako0938
Radu Constantin
HP (@banjohat)