Geiger Kit - GK-B5

Please note: Due to the chip shortage and other reasons, the GK-B5 kit will be phased out when existing stock is gone.

This page is intended to describe the main features of the GK-B5 kit. For full details, please refer to the Users Guide found on the GK-B5 Downloads page.

DIY Geiger invests a lot time and resources, not only in providing this open source code, but in the documentation below. Please support it by considering the original DIY Geiger Kit on this site, rather than knock-off versions that link to this page.

General Features:

• CPM and dose values based on moving average for the last 30 seconds. Updated every 5 seconds.

• A bar graph provides fast response to changes in activity (updates 20x / sec).

• A scaler screen that shows running counts / accumulated CPM and dose for the last minute and a user definable period.

• Serial output in CSV format is sent once every minute. (a USB to Serial dongle is required for this)

• Independent counters and periods for display, serial output, scaler, and bar graph.

• Low voltage warning displays when MCU voltage drops to 4.2V.

• Two switchable CPM to dose conversion rates, each settable allows for multiple GM tubes to be used.

• A settable threshold alarm to alert for high CPM levels (optional components may be required)

• supports Bluetooth connection to Android - see Android / PC BT Graphing

• I/O pins can be used to support other optional features

• Auto-precision - decimals are dropped from the displayed dose rate as it gets larger.

• Tone Mode Option - metal detector like tone instead of clicks.

Here are some of the main menu options:

• DISP PERIOD (MS) - The number of milliseconds before the display refreshes.

• LOG PERIOD - Period to write CPM, 'dose', and MCU voltage to the serial output.

• CPM->[DOSE] RATIO - Sets that ratio for the type of GM tube used.

• ALARM THRESHOLD - When the CPM or DOSE units is greater than this value the alarm is triggered.

• DOSE UNIT - Used to select the name of the unit for the dose value - "uSv/h", "uR/h" or "mR/h".

• ALARM UNIT - Sets whether the alarm is based off of CPM or the DOSE unit.

• SCALER PERIOD - Sets the user definable period for the second scaler.

• BARGRAPH MAX CPM - CPM that will give a full scale reading on the bar graph.

• TONE SENSITIVITY - Determines how sensitive the tone is to changing activity.

• USE RADLOGGER? - When "Yes" serial output is compatible with Radiation Logger application - see Android / PC BT Graphing page.

• REG. VOLTAGE - Displays the voltage powering the MCU (Vcc). To a large degree, this represents the state of the battery.

Tone Mode

Instead of the usual 'clicks', tone mode produces tones that vary in frequency with the current activity - much like a metal detector. There is also an associated "null" button that resets the scale to the current activity. Tone mode is very responsive to changes in activity, and the change in pitch is much more noticeable than a change in the rate of clicks. It was primarily designed for field surveying and as far as I know, no other Geiger counter has it.

The sensitivity of the tone mode is set by the TONE SENSITIVITY menu option. Sensitivity refers to the 'bandwidth' of the tone. Sensitivity can also be adjusted by adding an external pot. The BARGRAPH MAX CPM menu setting also affects tone mode by defining the CPM that will produce the highest frequency of tone. Normally this is set to highest CPM for situation and tube being used.In order to get the best spectrum of tones, tone mode is based on a logarithmic progression rather than a linear one. This fits with the fact that radiation intensity is inversely proportional to the square of the distance from the source.

The "null button" resets the range of tones so that the low notes are set back to the current activity. This is a useful feature when switching from a low to a high background for instance. The null button removes the higher background so increased activity may be more easily discerned.

External Controls:

This diagram shows the switches, buttons, etc. that are supported by the current board and software.

The controls you choose to use are up to you. The kit will work without any external controls, but you should at least add the Select Button.

The Build Instructions will have more details.

What's included / Availability

• The GK-B5 kit will contain all parts needed to build the base board with the ATmega328 processor.

• The mini-remote, and a blue/white 2x16 LCD is also provided.

• The GM tube is not included.

• A case, power source,and buttons and switches are also not provided.

• A USB to serial adapter is needed if you want to interface the kit with a PC. See the GK-B5 Software page.

The GK-B5 is available for purchase on the Buy the Kit page.