Simply put, the "Geiger Shield" is a daughterboard that plugs into the DIY Geiger Kit that provides additional functionality. It makes it easier to add an LCD display, and provides a menu system, but it's main goal is to provide logging.
You can get an idea of what it does from the video below:
The Geiger Shield is not essential. If you're not interested in logging to a MicroSD card, then it has only a few advantages.
In order to use the Geiger Shield you will need:
- a Geiger Kit with microcontroller (KIT-B)
PCB versions V2, V3 & V4 are OK but they do not break out the RxTx pins (only needed if using a GPS). V3b and V4 will.
- This Kit already contains a programmed ATmega328 Chip with Arduino Bootloader and the right sketch for this Kit. You just have to replace the microcontroller on your board. If you want to change your firmware yourself, you will need an FTDI cable, USB 2 Serial board or other USB-TTL adapter.
- a 2x16 LCD display (the contrast pot is already on the board) - see this page for suggestions on a LCD.
- a universal remote that can be set to a Sony TV. See the instructions for details.
- a MicroSD card Ė tested up to 2GB (which can take a huge amount of logs)
- (optionally) a GPS module. It should be 5V tolerant with a serial interface. Only tested with a EM-406A.
- a header to plug in the LCD
- a "GPIO" chip to drive the LCD with I2C instead of parallel. (this saves a bunch of I/O pins on the Atmega328)
- a header for the GPS module - but using a GPS is only an option
- a real time clock (DS1307) and backup battery. This is also I2C, and keeps the time and date if not using the GPS.
- a MicroSD card slot to hold the log files - a 3.3V regulator and buffer IC make it compatible with the 5V system.
- an IR Receiver so a TV remote can be use for input to menu options (see below)
- a set of 4 dip switches that can be used as needed
- all I/O pins on the main board are broken out on the daughter board
- a little breadboard area is also provided
To support the new hardware, a new sketch is needed. Nothing will display unless the new sketch is loaded! The current source code is available in the Documents section at the bottom of this page.
Please note that this Kit already contains an ATmega328 with the right sketch preloaded, so you just have to swap the microcontroller.
There isn't enough memory in the ATmega328 to support both GPS and non-GPS logging at the same time. Note that when a GPS is used, the time and date (in UTC) comes from the GPS output. When it is not used, a real time clock chip must provide it (along with the ability to set the date-time). So the solution to the memory problem is to use "precompiler statements" (#defines) so that only the functions being used will take up memory. All this means that without changing anything, the software will default to the non-GPS mode, and it will use the real time clock chip. For those who want to use the GPS, one line of code is changed and the program is uploaded to the chip.
The code for menus also takes up a lot of memory, and navigation for them requires hardware. To minimize the memory, the menus are somewhat different between the GPS and non-GPS modes. To make the hardware for navigation as simple as possible an IR receiver is used so that navigation is done with a universal TV remote (set to Sony) instead of adding a set of buttons to the board.
Initially, many of the options are set to defaults. The idea is that if you don't have a 10 key pad on your remote, you won't have to hit the arrow key 175 times to set the CMP -> uSv ratio! Note that the previous settings made have been stored in EEPROM on the ATmega328, so you tend to pick up where you left off. Here is a brief description of each menu option:
- SEC DISP PERIOD is the number of seconds before the display refreshes.
(5 seconds is a good setting. Display is now based on a "running average" like the Geiger Kit.)
- 1= DOSE MODE ON - Dose Mode shows the running average of CPM & uSv/h on an alternate display that comes up after 4 display periods have passed. It can also be activated by closing DIP switch #1 on the board. Note that Dose Mode will only begin to display once 1 minute has passed.
- MIN LOGGING is when to write the log data to the MicroSD card (in minutes). Zero means no log.
(Since the setting is in minutes, logged results will not be subject to rounding errors.)
- CPM->uSv RATIO is ratio for the type of GM tube used. 175 is the default for the SBM-20 and 100 is for the LND712. Unlike the "default sketch" only one ratio is supported, but now it can be easily changed.
- ALARM > CPM when the CPM is greater than this value, pin 15 goes high (+5V) what you do with it is up to you. Caution! If you exceed 40mA. You can burn out the pin. You can trigger a transistor if you need more than that. Pin 15 will go back to low (Gnd) when the CPM drops back under the alarm threshold.
- Date and Time In the non-GPS mode (only), you need to set the date and time. There are separate menu options for DAY, MONTH, YEAR (YY), HOURS (24), and MINUTES + SET. After minutes are set, the time clock will be set and you should see the correct date and time on the second line of the display. The date-time is backed up by the battery on the daughter board so it will stick.
Note that there is a compile option to automatically adjust for the US version of daylight savings time. There are also several other compile options to set the format of the date and time. By default, the format is DDMMYY 24Hr, but MMDDYY, YYMMDD, AM/PM can also be set. See the beginning of the sketch for these options.
- ZONE (>12= +) In the GPS mode (only), you need to set your time zone because the GPS provides time in UTC format. The time zone can be anything between -12 and +12, but avoid the complexities of entering negative numbers, values between 0 and 12 are considered negative, and above 12, positive. So if your zone is +5 you would set 17.
- OTHER OPTIONS Newer releases may have other options added to the menu.
Note: There are three SMD (surface mount) parts - IC1 & IC2 and the MicroSD card socket (left), which is probably the most challenging. These are not super fine pitch components, but soldering SMD uses a little different technique. There are lots of tutorials on this subject on the web (http://www.sparkfun.com/tutorials/36 is a good one). If the picture on the left doesn't scare you, you're good to go. :-) The vendor recommends a flux pen (water soluble) which makes the solder flow nicely, and avoids bridging. The assembly instructions also provide a few tips.
It is recommended but not mandatory that you power the kit with REG jumper installed. This means either 3 alkaline or 4 NiMH batteries, or a 5V power cube. The max current for the regulator is only 100ma, and with a GPS and an microSD card this can be exceeded.