Saturday, May 21, 2022

Gamma Dog - Performance

 So how does the Gamma Dog perform? 

The short answer is - fantastic! 

I am really happy with the performance. Charles and I have been testing our instruments inside and out and they work great - sensitivity is excellent so as the ease of use. The operation is a complete joy and a fun user experience just to go out in the field and hunt for radioactive minerals with the Gamma Dog. We seem to have nailed all of our design goals and there isn't anything I can think of to improve the instrument further.

Here is just a small fraction of the specimens I have collected with my Gamma Dog.

This little Euxenite crystal (on top of a US Dime for scale) I found under 2-3 inches of silt and sand in a wash near the pegmatite at White Signal, NM

This is the haul of Euxenite crystals over a couple of days Charles and I found in a single "honey" pot at White Signal, NM. 

I found this gigantic Euxenite crystal, one of the biggest I've seen - it wasn't difficult to find though, with an with activity of almost 8000 CPS, the Gamma Dog was howling. Charles found an unusually high-activity area and started digging a hole but then he attributed the activity to the "mass-effect". I decided to give the hole a second chance and it produced this fantastic crystal.

Another interesting Euxenite - the "corner" void was caused by a weathered quartz crystal which crumbled and disintegrated when I pulled it out. I guess the radiation onslaught over millions of years was too much for it.

A very interesting crystal habit of Euxenite (White Signal, NM) - I found the one on the left with my Gamma Dog and Charles found the one on the right. Both crystal are in the collection of Charles now. 
Picture by Charles David Young.

Allanite-(Ce) crystals I found over a couple of hourd with my GD at the Kingsman Feldspar Mine, Kingsman, AZ

Closeup of one of the Allanite-(Ce) specimens from Kingsman, AZ

Quartz with Copper ore and black Uraninite inclusions from the Green Monster Mine south of Las Vegas, NV.

Uraninite (the two on the left) crusted with secondary minerals (Gummite) and Zircon? (on the right) from the Biermann Quarry, Bethel, Fairfield County, Connecticut

A quick overview of the Gamma Dog.

Wednesday, April 13, 2022

Gamma Dog EXP - External Probe

The idea behind Gamma Dog EXP is to have a self-contained electronics module  which I can connect to various external probes. This allows a certain level of flexibility - detector using smaller crystal can be attached to a wand and used in the "Metal Detector" style setup, sweeping larger areas much faster or an alpha scintillator can be connected to check for contamination. I also use this setup very effectively during mineral shows (sans the wand) and I can quickly sweep across the tables with specimens.

The large internal detector unit is just too big and heavy to be mounted on a pole and the range of scanning around a person with it is limited to an arm's reach.

 This is the entire setup mounted on a "Metal Detector" style armrest and pole using a low-profile detector using 40x80 mm NaI(Tl) crystal

The self-contained electronics module came out pretty compact. It can be placed in a backpack or even hanging from a belt.

Over-the-shoulder strap is another, very convenient way to carry the unit.


`BNC connector for attaching the scintillating probe. Bias voltage is set internally (up to 1000V) and VD impedance of the PMT must be above 60MOhms.

Gamma Dog - skinned :-) the electronics only

The electronics modules for my Gamma Dogs - 3 are based on Version 3 Hardware and 1 unit (used as a Spare/Backup) - on the older Version 2 hardware.

My Gamma Dog pack - ready to hunt for radioactive rocks.

An inverse color scheme option is available in firmware 3.9
(Menu Selectable)

The mount for the detector was designed with TinkerCad and 3D printed with 100% in-fill for maximum mechanical strength.

Mount is comprised of a lower cup and a top cap. A threaded feed-thru is used to secure the cup to the bottom of the pole. I used a feed-thru to reduce weight and possibly add an elastic strap to pull-down the top cap.

The cap is designed with a slit for the BNC connector and cable. Cap slides over the pole and a pair of 0-rings - one on each side provide friction resistance. This facilitates easy installation or removal of the detector in just a few seconds. The friction from the o-rings is strong enough to lock the detector firmly in place.

If I need to remove the detector, all I need is to pull the top cap up and slide the bottom of the detector into the cup. To lock the detector in place I push the cap down and move the 0-ring right behind it.
The bottom cup provides additional mechanical protection to the detector housing.


This type of mount is fully adjustable for various detector lengths and diameters up to 2". Ill probably design another set for detectors with diameter between 2" and 2.5"

My 40x80mm NaI(Tl) compact detector in carbon-fiber housing, mounted at the end of the pole.

P.S. This is old but here is an article in Atlas Obscura on radioactive mineral collecting (shameless self-promotion:  I am quoted a couple of times and there are pictures of minerals currently in my own collection).

Wednesday, March 16, 2022

Low-profile Scintillating detector for Gamma Dog EXP

 For my Gamma Dog EXP (External Probe) I wanted to build small and lightweight detector to be mounted on a "Metal Detector style wand".

The weight is important as the detector is basically on the end of a long pole (which is great for covering larger area in a single sweep) and all of the implications from momentum and inertia of a large mass are present.  The pole becomes a lever in your hand the weight on the end is fighting changes in its state via momentum and inertia - according to Newton's laws it tries to stay in motion or tries to stay at rest and the results are amplified by the long arm of the lever to the operators hand. 

There is not much that can be done about the crystal - NaI(Tl) is a dense substance and at the end it comes to a compromise between weight and sensitivity. I decided to go with a 40 x 80 mm crystal. The length of the crystal makes it more sensitive for gammas coming radially to the canister - something which is an advantage due to the angle of the detector in relation to the ground surface (the metal detector wand on which it is mounted puts it at a fairly low angle)

To keep the detector assembly short and light I went with a very low-profile PMT - Photonis XP6242.
XP6242 has a hybrid multiplier comprising of a very large first dynode coupled to a foil multiplier.

The length of the entire PMT is about 10cm with the VD board on the back
It is a 10-stage PMT with Gain of 2.5x10^5 and supply voltage of 1000V

The photocathode's diameter is 48mm and the overall PMT diameter is 51mm which works out perfectly for a 40x80mm crystal. Photocathode is larger than the optical interface window of the crystal's housing which means no photons will be wasted. The size difference is small too - the canister's outside diameter is 46mm and the PMT outside diameter is 51mm which means there is no need for centering collar - just a few turns of electrical tape on the crystal's canister will equalize the size difference.

The Voltage Divider was made with 2R (K-Grid and Grid-D1) and R between the dynodes. I used 4.7M for R and 9.4M for the 2R

Since there is no standard 9.4M resistor value for the 2R resistors and the pcb pads are just for a single resistor, I had to use the "tent" mounting technique for these resistors. 
The total VD impedance is 65.8M - this is high enough to minimize voltage drop and works well with Gamma Dog's HV supply while improving SNR in case I use it for spectroscopy.

The VD board installed on the back of the PMT.
 A machined rear cap with a female BNC connector is installed over it. Before installing the cap, I soldered a strip of thin copper foil to the ground terminal and this foil is pinched between the PMT and cap, used to ground the Mu-metal magnetic shielding.

These "long" NaI(Tl) crystals are used mainly for oil logging - size is 40 x 80mm. 

Typical NOS Soviet-Era type crystal - nice and clear with no yellowing and blemishes. In Spectroscopy mode the resolution is better than 7%. Gamma Dog shows approximately half of the count rate of a 63 x 63mm crystal for natural background. 


The rest of the assembly is very straightforward - cleaning with acetone optical surfaces, applied optical interface silicon fluid between the crystal window and PMT, cap on the back with BNC connector, electrical tape, grounded mu-metal sheet (connected to ground with copper tape in order to double as an electrostatic shield for the PMT), a few turns of Mu-Metal around PMT overlapping the photocathode and VD board and then more electrical tape and foam.

For the detector housing I wanted something strong and light and the choices were titanium or carbon-fiber. I went with a carbon-fiber tube OD 64mm with 2mm wall. The detector assembly needed only one thin layer of closed-cell rubber foam to fit inside like in a glove.

Two 3D printed caps are used to close off the detector assembly.
The design of the caps is such that the carbon-fiber tube is inserted in a precisely sized groove in each cap. There is a beveled inner edge on the top cap sealing the enclosure against the inner detector cap.



The caps are glued with RTV sealant and provide dust and water resistance to the detector.

Tuesday, October 26, 2021

Gamma Dog - The Ultimate Radioactive Rock / Mineral Finder!

A friend of mine and an avid REE mineral collector Charles Young designed sometime ago an instrument intended specifically for finding radioactive rocks "in the wild". The design evolved from his initial concept to become a pretty clever and viable solution. Charles and I have been talking for awhile, exchanging thoughts and ideas what such instrument should be and what features are needed. Finally, Charles managed to do something I've been thinking about for years but never really had the time or the proper motivation to dive into! His work was truly an inspiration for me and eventually precipitated as the "Gamma Dog project" as I realized I am not alone in my ideas to create a radioactive rock-finder.

With the core R&D work done by Charles, we decide to collaborate in the design efforts and improve both, the hardware and software side in order for this instrument to become the Ultimate tool for the Radioactive Rockhound.

Currently, there are no such specialized prospecting tools as the Gamma Dog on the market. The glory days of Uranium and REE prospecting are long gone! Consumer grade radiation detection is reduced mainly to inexpensive Geiger counters and dosimeters. The few commercial detectors intended for professional use by geologists are extremely expensive yet lacking some important for us functionality.

Geiger Counters are more or less useless for mineral collecting due to their poor  gamma ray sensitivity and commercial scintillators on the other hand, require that your eyes are "glued" to the meter's scale in order to monitor for a detected rate increase or you have to listen to a divided click-rate and trying to figure out if the click rate changes , just "by ear", which is a pretty strenuous activity by itself. 

We wanted something which is simple to use, very sensitive and allows the user to focus on the environment / terrain and not on the instrument itself. Such instrument must be something really intuitive to use and this will make the activity of radioactive rock hunting more enjoyable than simply staring at a meter, while waiting for the needle to jump or a number to increase. 

Meet the γDog! 


The instrument's housing is a 14.5" long, 4" diameter ABS plastic tube with two end-caps, a few handles and attachment points and a control panel located on the top cap. Weight is ~5.5 Lbs when equipped with 63 x 63mm NaI(Tl) scintillation crystal. 

I think, the outside look is a bit ominous and I'll probably need to dress it a bit with some decals for the sake of the public. After all, you press a red button on a big, black, cylindrical object - it beeps and the first thing you see on the display is the radiation trefoil - I can see how an ignorant or less intelligent person could hyperventilate seeing this.

The 3 major internal components are the scintillating detector, electronics package which includes an advanced microcontroller, pulse amplifier and HV power supply, along with other boards and components and the 6600 mAh LiPo battery (there is also a coaxial cable interconnect between the electronics and the detector).
The scintillating detector is heavily padded with closed-cell rubber foam ("Neoprene") to protect the delicate crystal and PMT from any mechanical shocks and vibrations and to provide thermal stability for the crystal. The unit can accommodate different LiPo battery sizes - usually 2x18650 cells in parallel (4400 mAh) or 3x18650 cells in parallel (6600 mAh). The bottom ABS cap is solvent-welded and it is water-tight. The top cap is removable (3x SS Screws) and hosts the entire Electronics module and control panel.

The Latching Relay board (left) and MCU board (middle) are stacked on the motherboard (right) headers. Visible between the headers are the 12-bit DAC and 4K EEPROM boards. The red solder mask PCB is the HV power supply, pulse amplifier and decoupling circuit.
Currently, I am prototyping the latest version (v3) of the Gamma Dog. I designed the PCB with AutoCAD Eagle and the fabrication was done through the OSHPark service - the PCBs came out absolutely superb with a beautiful purple solder-mask and gold plated pads and vias! Highly recommend OSHPark for small projects - quality, pricing and ordering process are simply fantastic!

The new hardware version expands on the v2 PCB with a second control button for an improved UI, 4K EEPROM for storing settings and internal data and a 12-bit DAC for digitally adjusting the value of the Pulse Height Threshold.

There is an RFI can for shielding the HV circuit with hole to access the HV Adj. Potentiometer - the red board on the right (the RF shield is yet to be installed in this picture).
There are 6 connectors on the motherboard - one female BNC for connecting the scintillator and 5 others for power, buttons, display, speaker and LEDs (4 connectors are on the top side of the board) - not counting the IPX to SMA coaxial connection.
Not pictured here is the latching relay shield which plugs into the top MCU headers. 

A quick demonstration of the "γDog v2 PLUS" and the UI.
(Youtube link)

Hardware Features:

Most of the instrument's housing is occupied by the padded scintillator (see the diagram above). There is also a battery "compartment" and the entire electronics assembly is located in the top end-cap. A fixed metal handle with a soft nylon strap handle and a a couple of special finger pulls / attachment points facilitate easy handling and maneuvering of the instrument while searching and digging. The enclosure is sealed and water-proof up to the control panel so it can be partly submersed if needed. The control panel is water-resistant and can withstand occasional splash of mud, water or light rain and it is easily protected with a transparent plastic "shower cap" and a rubber band when weather conditions deteriorate severely. There is 1/4" thick Plexiglass bezel protecting the display.

  •  Large (63x63mm NaI(Tl) crystal) Scintillating detector - this is the detector I previously built, but almost any NaI(Tl) / CsI (Tl) / CsI (Na) scintillating detector can be used or even Bicron BC408/BC412 Plastic scintillators. Requirements are: a voltage divider impedance of 50M-120M, common signal / PMT HV bias line and voltage up 1000V - Ludlum 44-2 probe for example is one possible "off-the-shelf" solution.
It was time to put my newly built large NaI(Tl) scintillator to work. 

My large 63 x 63 mm NaI(Tl) detector is the "heart" of the γDog and covers the "traditional" for NaI(Tl) detectors Gamma rays energy range of 25keV to 3000 keV. The larger the crystal is, the more efficient and sensitive the instrument is going to be - this is critical when looking for radioactive specimens "in the wild", which can have very weak emissions due to the shielding effects of soil and rocks and/or low N.O.R.M. content. Smaller size detectors or scintillating plastic detectors on the other hand are better when searching in tailings piles, mine dumps or inside mines, where the radioactivity is abundant to begin with.

  •  Adjustable, regulated and filtered, boosted High-Voltage Power Supply for the PMT Bias, positive polarity, outputting in the 600V-1000V range with 4V input. The low-voltage supply rails of the HV PS is controlled with a latching relay for a reduced power consumption.

γDog's High-Voltage Power Supply and Pulse Shaping Amplifier.
  •  Pre-amplifier with adjustable gain ratio and adjustable pulse shape - rise/decay time-constants as well as decoupling capacitor and load resistor are all hosted on the HV board as well.
  •  Adjustable minimum pulse level detection threshold using a comparator on the input of the MCU to "digitize" the scintillator pulses for counting.
The scintillator pulses as they are amplified (yellow trace) are "digitized" by the comparator (blue trace) when they exceed the preset voltage threshold (white cursor trace on the Y axis).

Nordic nRF52840 System on a Chip is the "brains" of γDog.

  •  Nordic nRF52840 SoC (installed on the Adafruit Feather Sense Board) - ARM Cortex M4F processor, 1MB Flash and 256K SRAM, 21 GPIO, 6 x 12-bit ADCs, up to 12 PWM outputs and an array of environmental sensors - Accelerometer, Temperature, Humidity, Magnetometer, Barometric pressure, etc. as well as Bluetooth LE connectivity.
  •  Amplified (Class D amplifier) panel-mounted 1W speaker with manually adjustable volume
  •  3 backlit buttons (Power, Squelch, Display Mode) with indicator LEDs
  •  High-contrast, ultra-low power SHARP Memory eInk graphics display (144 x 168 pixels)
  •  Rugged Micro-USB port (/w protective cap) for battery charging and firmware updates. Use-while-charging with an external 5V USB battery pack is also possible. 
  •  Built-in LiPo battery charge controller with 200mA charge current
  •  6600 mAh / 3.7V LiPo Battery (or 3x 18650 cells in parallel) which provides up to 24 hours of continuous run time. Smaller capacity battery can also be used - 2x18650 (4400 mAh) and will still provide a full day of continous operation while reducing the weight.
  • BLE or Low Energy Bluetooth connectivity for outboard data processing and storage (on a Smartphone or PC)
  • Configurable BT power levels

Software Features:

There are a couple of novel features which make this instrument different than anything else out there - the count-rate based variable frequency tone feedback coupled with an adjustable level squelch control. Both features are aimed at easy detection and location of radioactive sources. 

Listening to slow clicks while trying to adjust to the background count rate in order to detect any changes when radiation is detected is way too strenuous on the brain - changes in the pitch of a tone on the other hand are picked up immediately and very easy to follow. The squelch control on the other hand makes the instrument "vocal" only when needed, near a radioactive source above background level.

Gamma Dog is running on almost 3000 lines of code (firmware V3.9.2)

  •  Audio is main method of feedback via the variable frequency tone and alert beeps.
  •  Super-simple and responsive 2 buttons UI with click, double-click and long-press actions (all with audible feedback) to execute various actions such as Sql Level Adjustment, Auto-Set, etc. 
  •  2 user-selectable persistent display modes - Current Rate and Rate vs. Time Histogram.   
  • In the Rate mode, single-click of the Squelch button will increase the squelch level and double-click will decrease the level. Audio frequency will increase 10Hz for each 10 CPS and displays shows numerical count rate.
  •  In the Histogram mode - display shows 140 seconds scrolling count-rate histogram and double-click will toggle between constantly open Squelch and Normal Squelch Control. In addition, in this mode the audio is generated with smaller (5Hz) steps per 10 CPS. This mode can be useful when searching in places with many high-activity sources like mine dumps / tailings. etc. as very high rates will keep the audio frequency half of the rate - i.e. 4000 CPS will result in ~2kHz tone when squelch level is set really low.
  •   2 indicator LEDs - Green Squelch button LED flashes when the number of counts reaches 2x the squelch setting counts and also indicates the startup sequence point for Histogram mode change, Red Power button LED indicates sleep status / HV power off (when blinking) and normal operation (solid glow)
  •   Graphics display shows Firmware version, Internal Diagnostic results and alerts, Current Count Rate in CPS (refreshed every second, resolution 10 CPS) or a count-rate rolling histogram, battery level as voltage and percentage of capacity (refreshed every minute), Current Squelch Level Setting, Count Overflow and Low Battery Alerts.
One of my contributions to the project was the development of the display interface and the firmware code for it, including the UI. γDog PLUS uses 1.3" Ultra-Low Power SHARP Memory display (144 x 168 pixels, same kind as the one used in the Pebble Watch). The display is a very high-contrast eInk type, super-easy to read in direct sunlight, recessed in the front panel for mechanical protection and it shows useful information improving on the ergonomics and the interaction with the instrument.
Data on the display is refreshed every second for the Count Rate readout and every minute for Battery-related information.

  •   Internal diagnostic routine reports over-temperature, water intrusion (by measuring the internal air humidity level in the enclosure) and various levels of the battery condition - both visually, on the display and with a series of beeps.
  •   Audible and on-screen "critical battery level" reminder - every minute when voltage drops bellow 10%
  •   On-screen Charging / Charge Complete Status Indicator
  •   Complete bootup time from Power button press to Ready to use is 12 seconds.
  •   An Advanced Accelerometer-based PMT / Battery saver will shut down the High-Voltage Power Supply and the pulse pre-amplifier after 10 minutes of inactivity (no instrument movement) during normal operation or after 1 minute while charging the battery overnight. The normal operation resumes within 1 second of the instrument detecting a physical movement (for an example - picking it up). During normal operation the red power LED glows solid and blinks when the instrument is in Sleep Mode. I designed this feature with the use of a latching relay to further save power. Going in and out of sleep mode is accompanied by an audible feedback (descending or ascending tone chirp). Current draw drops from 70 mA to 10 mA when the HV supply is powered down. The DAC is also powered down during sleep. There is also selectable "No Sleep" mode as well as "Charge and Sleep" mode.
  •   Auto-Squelch Set will sample and establish the squelch trigger level at the current sampled background radiation level during startup or when it is activated by the user with a long-press of the Squelch button.
  •   Tone frequency generation is set always to begin at the current squelch level and frequency always starts low when the squelch opens, regardless of the current rate or range of operation - this allows for the instrument to operate in a comfortable for the human ear frequency range regardless of the current measured count-rate. In other words, the lower end of the audio tone frequency range is dynamically adjusted to begin at Squelch level. 
  •   Histogram Mode displays scrolling and auto-ranging relative count-rate histogram

The scrolling count-rate histogram displays the count-rate history over the last 140 seconds. The histogram is dynamically normalized to the count-rate range over this period of time with the minimum count-rate overt the past 140 seconds on the bottom.

Typical background rate histogram (130 CPS to 200 CPS). 
The histogram is constantly updated in background at 1 sec intervals and always available for the last 140 sec. It displays also Min, Max and Average Rate.

High-rate event (2560 CPS) (specimen of Uraninite), followed by drop to background level. 
The displayed histogram is scaled to show the maximum rate peak which on the other hand "pushes down" the background level.
  •   Response to count rate changes with a pre-set hysteresis which prevents the squelch from opening during short rate fluctuations.
  •   Excessive Count Rate / Overflow alert above 10 000 CPS (600K CPM) - the maximum rate is not really limited but the count accuracy will drop when excessively high rates are detected.
  •   Compensated count accuracy for overall error in counting of 0.1% (electronics only)
Test of the hardware and the software counting algorithm. Feeding the input with pulses from a function generator shows that the counting accuracy is spot-on! Maximum error is 10 CPS.

Test Setup for counting accuracy and pre-amp alignment.
 Maximum count rate is up to 17K CPS (~1M CPM) for short pulses (~50 uS). Average pulse length of 100uS will allow count rate of 10K CPS (600K CPM).

   Instrument Usage

Sensitivity comparison between γDog and a Geiger Counter - there is no contest!

(Youtube link)



Charles Young showing his field use of the standard model Gamma Dog.
(no display and indicator LEDs but otherwise almost identical)
(Youtube link)

Prospecting for Radioactives in New Mexico - Charles Young, August 2021

(Youtube link)

Prospecting for Radioactives in Southern New Mexico - Charles Young, November 2021
(Youtube link)

UPDATE: development of Version 3 hardware and firmware has been completed. The UI is now using 2 buttons - it was specifically designed to improve the user-interactions and ergonomics if display output is also present. 

The UI can now adjust the Minimum Pulse Height Threshold. This parameter along with another 8 configurable parameters are saved in the unit's EEPROM. Adjustments of the Pulse Height Threshold are done using a 12-bit Digital-To-Analog Converter (DAC) and displayed in millivolts (accuracy is better than 1mV) while the device is running in normal counting mode - this way the result of the adjustment can be seen immediately. There are UI coarse and fine steps while changing this value.


Additionally, there are 13 items in the Configuration Menu as well as a "Reset to Defaults" feature which re-writes the EEPROM with the default values.

The Version 3 hardware installed in the front panel cap.
Only 2 connections are needed to the body of the instrument - coaxial cable with BNC connectors to the detector and a connection to the LiPo Battery pack.

Current draw for the v3 hardware is 68mA during normal operation mode with Squelched audio and only 10 mA during Sleep mode.

The Blue button is the Squelch Control (UP/+), the Green button is Display Mode and Squelch Control (DOWN/-) and the Yellow button is the power ON/OFF switch. The user now can toggle and latch the squelch control open/close by a double-click of the Green button. Squelch Auto-Set is activated by a Long-Press of the Blue button.

Version 2+ (/w one button UI) on the left and Version 3+ (/w two buttons UI) on the right.

Bluetooth connectivity 
Gamma Dog is equipped with a Low Energy Bluetooth connectivity (BLE).

Bluetooth can be enabled/disabled from the configuration menu. On startup, Gamma Dog will automatically start advertising, waiting for connection.

5 levels of BT Tx Power can be set from -20dBm for level 1 up to +8dBm for Level 5.
This menu item is context-sensitive and will show up in the menu only if BT is enabled.

There are two different BT icons, indicating in total 4 different states of the link - whether there is a currently active connection or not and whether BT data streaming is on or off.
 Double-click of the Squelch button toggles the data logging on/off and the BT icon blinks showing Data logging is in progress.
Data logging is automatically suspended during Sleep Mode and resumes on wakeup.

 A string of parameters is broadcasted over BT every second and includes various internal parameters, detected current Count Rate and Squelch Level. Each data set includes a rolling counter as well.
 Currently, the data can be received with the free Bluefruit Connect App in UART mode or Plotter mode. Commands can be send back to the Gamma Dog to toggle on/off the logging mode and to stamp "Waypoints" with GPS coordinates. 
There are plans for development of a companion Cell Phone App which will store the received data while stamping each set with the current GPS coordinates and a time-stamp. Parsing this data and converting it to Google Earth KML/KMZ format would be next logical step. Overlay over the terrain showing the path with current rate and "waypoints" of found minerals will be a pretty powerful and useful prospecting tool.

The Bluefruit Connect plotter mode shows Count Rate vs. Time Graph (orange) and Squelch Level changes (blue).

Firmware Update v3.7:
- Added a menu-selectable Sleep & Charge mode - useful to charge the internal battery of the instrument from an external power source (car) or battery pack while in constant motion - during hiking or a car ride when the constant movement otherwise will prevent it from going into Sleep Mode. When this mode is activated, the Gamma Dog will startup normally, it will Auto-Set the Squelch level but it will fall to sleep unconditionally within 12 sec of startup. The device will not wakeup due to motion in Sleep & Charge mode. Pressing any of the two buttons is the only way to wakeup it up and resume normal operation.
- Added Automatic Squelch Auto-Set (ASAS) mode. Useful as a  "Smart Searching mode" while moving through areas with different radiation background levels. This feature reduces the need for manual squelch auto-set when searching. When this mode is activated, the Gamma Dog will automatically execute Squelch Auto-Set if:
    (a) The Squelch has been constantly closed for a predetermined amount of time (menu selectable 30/45/60 seconds) AND the set squelch level is more than 100, 150 or 200 CPS (menu selectable) higher than the currently detected rate. This condition occurs when squelch has been set in a "hot area" and then the instrument transitions to an area with lower background levels. The ASAS mode will normalize the squelch level bringing it closer to the current rate thus removing the large gap which occurs between the current rate and the squelch level (a situation which otherwise will make the squelch less efficient and and will necessitate a manual Auto-Set)
    (b) The Squelch has been constantly open (30,45 or 60 seconds - menu selectable) and the detected rate does not peak higher than 25% to 150% (menu selectable) of the currently set Squelch Level. This condition occurs when Squelch is set in low background radiation area and a transition has been made to a "hot area" where the higher background keeps the squelch constantly open. Again, the Auto-Set will normalize the squelch level.
If a specimen is being located causing the squelch to stay constantly open but also detecting more than pre-set level of spike in the current rate, this will reset the timer in order to prevent an auto-set while trying to pinpoint the location of the source.
Each of the two timeout timers will reset if a corresponding change of the squelch status occurs.

Firmware Update v3.8:
    - added a menu item to set Smart-Squelch timeout - 30, 45 and 60 seconds
    - added a menu item to set Smart-Squelch Closed tolerance Level:
         4 levels from 100 to 250 CPS in 50 CPS steps
    - added a menu item to set Smart-Squelch Open Reset Level:
         rate peak will reset the Timeout timer if exceeds the squelch level by 25%, 37%, 50% and 62%
    - added 2 more audio frequency modifiers - x0.5, x1, x1.25 and x1.50
    - added "Charge Completed" battery indicator
    - various code optimizations, improvements and fixes

The Gamma Dog family.

Firmware Update v3.9:

    - added "Auto Audio Frequency Multiplier" - activated with the menu system, in this mode the audio frequency multiplication factor will automatically and dynamically be adjusted, based on the difference between set squelch rate and current rate. Change is done in 3 steps - 100-125%, 125-150% and > 150%
    - added a warning msg if the USB charging cable is plugged in but the power button is not pressed - the instrument will halt the bootup and will wait for a power switch activation. The "stop and wait" point prevents the instrument from startup if nominal voltage is not present on the power rail.
    - reworked the power-saving / sleep mode logic. Now the instrument will startup with normal Time-out delay (duration is set via the config menu system). Gamma Dog will only switch to the short 1 min Sleep Timeout if it detects that a charging cable is plugged in. Disconnecting the cable will cancel the short time Out. If no movement is detected 30 sec to 1 min after the charging cable is plugged in, Gamma Dog will fall asleep. Waking up will restore the normal timeout even if the charging is still going on - this allows for normal operation when charging in the field with an external battery pack. This, more elegant solution is possible by monitoring the status of the on-board charge controller.
    - added startup shortcut to "Sleep and Charge" Mode in addition to the menu selection
    - added a menu item to change the Display Color scheme - Normal (black on white background) or Inverse (white graphics on black background)
    - added second, fast histogram mode - menu-selectable histogram now will display the rate for the last 140 or 45 seconds.