Prepper Geiger Counter

The image at the top left is of a working prototype from November the 7th 2014, assembled as analogue click only.

The image at the top right is a silk screen overlay print of the new board design, currently waiting for the boards to arrive, 17 Nov 2014.

Below is a time line of the Geiger counter development starting October 2014

I have decided to produce a Geiger Counter printed circuit board not using any surface mount parts that is suitable for people used to working with through-hole components. Below is a list of some of the design criteria.

1/     The Geiger counter will be available in a kit form or as individual key components.

2/    The board can be assembled in many different configurations. See below.
  • Simple "click only" with low component count, the Geiger-Muller tube is the only speciality item, no micro, no software required, easy to build, very reliable , no speciality transformer used, the Geiger counter is expected to last for decades.
  • Add a rail-to-rail op-amp and a 1mA meter for a visual display (linear scale required). 
  • At any stage a few extra components can be added for enhanced operation (better high voltage regulation).
  • Add a 28 pin micro-controller and the optional LCD, many of the above analogue parts need not be fitted if the micro is fitted.
  • Install extra parts for enhanced operation, for example built a in voltmeter (handy for DC off grid systems)   
  • Bluetooth connectivity for use with computers, or android devices.
3/    Extensive spice and functional testing.

4/    Include lots of well written printable documentation for easy assembly by novice builders. Schematics will be published for those more advanced in the art.

5/    Have spare I/O's, for those skilled in the art of pic micro-controller programming. The boards can be used for other apps. All micros are plug in for easy updates by the semi-skilled.

6/    Measurements taken from the Anode not the Cathode for better performance with most Geiger Muller tubes, this enables the outer metal cathode to be grounded for better RF, hum and noise rejection. The board can be configured for anode or cathode operation.
11 October 2014

The design has been spice tested, the schematics have been drawn up and the PCB design is well under way, the PCB measures 100 mm by 100 mm with 3 mm mounting holes in each corner, input voltage is from 9 volts to 24 volts, current used will depend on the components installed, no firmware has been written, I have however used the 16F1783 and its big brother the 16F1789 before so a lot of code can be reused and modified. In its simple form it will run the default program, a single plug in jumper will select one of three different programs, an external rotary switch or pot could select more options.

It can take up to 4 weeks to receive the prototype board back from China, so I will be busy on this for a couple more days then nothing until the boards return.

6 November 2014

The boards have arrived from China and I have assembled the high voltage generator, it seems to work fine, with luck later tonight the audio output will be assembled and it should be clicking away, I have some radio active thorium to test it with.

7 November 2014

Assembled with speaker, works as designed, image below. This is almost the minimum build, the board could be cut at the white horizontal line and still work, the green terminal block for the meter connection need not be fitted. Apart from the Geiger Muller tube and circuit board, all the parts should be available from your local electronics hobby shop. The IC's are 555 timers, the larger diodes 1N4007's, the small diodes 1N4148, I believe a 1N4007 could replace the 1N4148.
The click has a good sound, a larger speaker or horn speaker could be fitted.

A Russian SBM-20 tube is fitted this has been described as the quintessential Russian tube. Some types are a waste of money, if in doubt buy a SBM-20 (Beta and Gamma only).

Fitted the remaining parts (below the white horizontal line) and tested the meter drive circuit, it worked as designed. BTW spice testing of the meter drive circuitry shows it be very linear.
It is be possible to use the 0 to 1 mA scale in some meaningful way for example 0 to 1000 CPM or 0 to 10000 CPM.

The analogue board works well, some of the soldering requires considerable skill and good eyes, I shall endeavour to make it a little easier.

8 November 2014

A version with the micro controller was tested, although it works very well as first produced many changes will be made to the PCB, I want it to use a micro that has a good free compiler available.

9 May 2015

This project is on hold due to high work commitments, development will eventually continue. 

25 Feb 2016

This project has not been forgotten and will be completed some day :-)