DIY/Homemade Radiation Geiger Dosimeter

[radu.motisan]

Given all my previous experience with Geiger Counters (see for example my uRadMonitorproject), I have decided to conceive a portable, easy to build, radiation dosimeter . I didn't have much need for yet another dosimeter (with my Radex 1706 or Terra-P), but I know there are several people not affording a commercial unit, but wanting to have their own radiation measurement tool. So here is this article, giving you just that: an efficient, stable, easy to build construction for all your radiation dosimetry needs.

Short description
I started from scratch, designing a complete dosimeter unit around the Atmel Atmega8 microcontroller and a Russian Geiger Muller tube. Here you'll see the CTC-1 tube, for high gamma doses, but the dosimeter can be used with any other tubes such as SBM-20, LND-712 or more sensitive ones such as the SBM-19 or the pancake tube SI-14B. Changing the tube requires changing the software, to adjust the dose conversion calculation. This circuit can be used with almost any geiger tube, as even the inverter's output voltage driving the tube is adjustable in the software.

Similar to my uRADMonitor, the microcontroller takes care of everything:
1. Generates a variable duty PWM signal using Timer1, to drive the 400V inverter needed to operate the Geiger tube; The invertor doesn't need a multiplier, as the ferrite's transformer secondary puts out exactly the amount required. The transformer is made on a A22 ferrite core, with 16 turns in the primary and 600 in the secondary.
2. Uses one ADC port to measure the inverter's voltage and adjust the PWM duty cycle for constant output (exactly 400V for stable operation)
3. Counts the time, using Timer0 so we can compute the dose
4. Uses interrupt INT0 to count the pulses produced by the Geiger tube
5. Drives a 2x16 LCD to output the results.
Some other circuits on the Internet come with improper 400V inverters (some people seem not to be able to design a proper inverter), they are redundant (using 555's and additional components, when the microcontroller can take care of EVERYTHING), use the wrong signal detection/counter circuit, or other small defects that result in wrong measurements. Not to mention the complicated aspect of computing dose in sieverts out of counts per minute.
Given all these wrong designs, my detector tries to fill in some of the gaps. So here is exactly what you need: a stable design, with several improvements made over time, all packed in this nice construction that you can easily replicate.

Some pictures


Circuit diagram:


Eagle SCH and PCB files:


I plan to add an UART Bluetooth module to enable remote operation (readings can be received on a phone running Android OS - I'll write a simple app for that), and a demo video - just didn't have the time to make it yet.

The software:
Here is the hex file needed to program the atmega8 : http://www.pocketmagic.net/wp-content/u ... 12/GMD.zip . More versions will follow as the project evolves.

[radu.motisan]

You might be familiar with the The CD V-717 that was designed for use in fallout monitoring stations. This detector has a removable bottom with a 25 foot extension cable. The detector element (ion-chamber) is mounted inside the removable bottom. This allows for the placement of the detector element outside of the shelter area while the metering section of the metering unit would remain inside of the shelter area connected to the detector with the 25 foot cable.
In a similar fashion remote operation is possible on my dosimeter, by using... Bluetooth. Hooked to the main microcontroller, there is an UART Bluetooth module packed with its 3.3V regulator. The software running on the atmega8, sends measured dose rate values, via UART (Rx/Tx) to the Bluetooth module.


By doing so, a mobile phone can be used to read the radiation data, from a remote location, without being exposed to what the dosimeter actually measures. Currently I wrote an application for Android phones, that can search nearby bluetooth modules, find the dosimeter, connect to it and display the dose rate, as received via the radio connection. Here is a demo video:
Video: http://www.youtube.com/watch?v=Fd8D6guu ... r_embedded
A first version of the Android software is available here: http://www.pocketmagic.net/wp-content/u ... ndroid.zip

Here is a video showing a high count rate when using a Si12b tube and Am241 alpha emitter from a smoke detector. Please disregard the uSv/h indication which is most likely incorrect for this particular case:
Video: http://www.youtube.com/watch?v=de_A6qBK ... r_embedded

The dosimeter allows changing the tube, via the small white jumper. The built in STS-1 gets disconnected, and a connector can be used to attach another tube, like I did with the SI12B . If case surface space allows it, I'll try to put a nice BNC connector of some kind.

For more details, see the complete article at: http://www.pocketmagic.net/2012/12/diyh ... -dosimeter

[radu.motisan]

This one also received an update: an UART Bluetooth module for wireless data transfer capability, and a software for Android phones, that can read the data an display it conveniently.


Reminds me of the old CDV-717 with the long remote cable for remote readings. Source code for the dosimeter and the Android application are available here: http://www.pocketmagic.net/2012/12/diyh ... dosimeter/
Yet an another example of an microcontroller-android os hybrid application.

Thanks to Andrei Borosovici, I had the chance to discuss this topic on "Vezi ce-ti doresti" TV Show running on TVR Timisoara. Here is the 14.01.2013 recording, in Romanian:
http://www.youtube.com/watch?v=WXmPR-FNbIg