Electronics > Projects, Designs, and Technical Stuff

Ultra low-power Geiger counter

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Teal:
I'm making a fully open source very low-power Geiger counter capable of running for decades on a single 950 mAh CR1/2AA Li-MnO₂ battery.

Here's the old less efficient version that's been proved to run for a year on two LR44 cells (~19 uA consumption):


I'm also posting detailed project logs on Hackaday:
https://hackaday.io/project/187553-compact-low-power-geiger-counter

In the new version the booster consumes only 0.5-0.6 uA at background radiation level (0.33 CPM) and the microcontroller consumes 0.55 uA (0.4 uA on RTC, 0.15 uA on LCD). The CPU consumption is negligible as it runs at 32.768 kHz and active for ~30ms once in a few seconds, so the total consumption is around 1.1-1.2 uA. Such a low power consumption is achieved by using a boost converter with an autotransformer where feedback is taken from primary winding (see schematic below) and a RL78/L13 microcontroller, in which the LCD driver uses a capacitive voltage divider instead of resistive one, and there's an option to disable the charge pump too.



The project is still in an early development stage, here's the features that I'm planning to have:

- M4011 GM tube with an energy compensation filter
- Dose rate measurements in Sv/h and CPM, alarm if a user-adjustable threshold is reached
- Absorbed dose measurements in Sv and counts, alarm if a user-adjustable threshold is reached
- 120 KB of memory to store the dose measurement logs, which is enough for over a year at 5-minute intervals
- Display of time passed since the absorbed dose measurement has started
- Self diagnostics: failure detection in the HV converter, GM tube, flash memory and clock generator
- Software-based resilience to single-event upsets in RAM
- USB-UART interface to connect to external devices and browse the logs or send data to the aggregators like radmon or radioactive@home; advanced options in the PC software are also planned like firmware update, tube calibration, UI tweaks etc.

Questions:

1. I want to have a phosphorescent layer on the bottom on the LCD for passive backlight, a paint or a tape maybe, is it possible/viable to have it applied during the LCD manufacturing? I couldn't find any LCD manufacturers that would do this, only DIY mods on Reddit.

2. I'm not sure about the form-factor; which one do you think is better, the round / hexagonal marker pen or a regular box?
The former is more compact, more convenient (?), and it just looks better — but the latter should be more sturdy and easier to 3D print / manufacture; there are also off-shelf enclosures of a suitable size.
Additionally the box allows the device to have a larger LCD, though I'm not sure how to use the extra display area.





3. Are the menu controls and the LCD layout good? The UI has to be intuitive as the intended use case is to throw it into a pocket or a backpack and forget about it for a long time.
Few people are going to remember the controls when tweaking them once in a blue moon, I'd imagine. I've attached the menu block diagram below.
Here's the LCD that my colleague designed:



— logging enabled
— dose rate alarm set
— absorbed dose alarm set
— clicker enabled
— battery level

And here's the the JS demo for the UI (alarm/failure sounds and messages not implemented):
https://plnkr.co/plunk/EDuPNBUZYkALeRak

Will be glad to hear your thoughts about the design!

Phil1977:
Nice project!

Two questions/ideas:
- Can it make direct "clicks" on the buzzer if an event is registered?
- What is the integration window time for the dose rate? A short time is preferred if you e.g. search for a radiation source and want quick response if you scan an area. A larger integration window greatly surpresses false alarms if you use the counter as a personal dosemeter and want an alarm if you are exposed to steady radiation, but not if you only have a short radiation burst. Of course the accuracy of the dose rate also gets better with a longer integration time.

If the device generates "clicks" then you could use the clicks for scanning and a longer averaging integrator for the dose rate display. Quick response of the uSv/h display is not that important if the clicking gives you a good feedback.

From my point of view the pen seems much more attractive. A combination of small outline, long living battery and low price would be great. Maybe it could have form factor so that its similar to the Radiacode 102/103 - so you could have one device for permanent surveillance and one for higher sensitivity and spectral analysis.

Teal:
Thanks!

Yes, it can make clicks, and this function is programmed to be core independent, so the clicking will continue for some time even if the software fails. Here's the demo of the old version:
https://imgur.com/a/AyuMUU5

The integration time is 1 minute, and it's a good idea to make it adjustable now that you mention it. I remember now seeing a few dosimeters with fast/slow integration setting. I'm also thinking about using LWMA / EWMA Instead of a regular moving average to increase the response speed to fast changes in dose rate while keeping the integration window long. Not sure yet how this will impact the accuracy though.
Another idea is to adjust the averaging time dynamically, say, if in the last  seconds were registered more than 100 events, the averaging window becomes 10 seconds long and the display updates twice in a second instead of once in 2 seconds.

Not sure about the Radiacode, I should figure the UI and the LCD layout first to be able to make small adjustments to the enclosure. But the box version that I've posted seems quite similar to the Radiacode.

Phil1977:
The radiacode sets a real benchmark for how much radiation detector you can get for around €350 in an EDC-package.

It is a scintillation detector with a special photodiode instead of PMTs. It´s packed with features, it has complicated menus, needs a PC/Bluetooth cellphone for full possibilities and you have to charge it frequently.

I don't want to advertise for it in your thread (though I probably somehow do...) but want to say an always-on-companion with a display and menus that are dead simple would make a perfect match for enthusiasts or people living in contaminated areas: Using and always-on-Geiger-Müller-Tube as a personal dosemeter and a small scintillator for first analysis or scanning for sources.


Damn, the time I was on university you would have spent the worth of a small luxury car for this setup! Now you can carry it for a fraction of your salary in your pants pocket...

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