Each unit is equipped with Geiger Muller tube „SBM-20“as adequately sensitive Gamma ray detector. These tubes are low cost and widely available as former USSR military surplus. Microcontroller inside unit, with accompanying developed firmware, serves multitude of purposes: generating PWM pulses for DC/DC converter, keeping track of number how many photons of Gamma radiation collide with the GM tube in 60 seconds period, calculating derived values of equivalent dose of radiation in nSv/h for periods of 60 seconds, calculating and keeping track of average values for period of 60 minutes, keeping track of historical average values of last 12 hours.
Microcontroller inside the unit is also playing a role of a web server, using the Microchip™ TCP/IP stack with custom added functionalities. Each unit has Ethernet port, and connected to DHCP enabled router, via the DynDNS service is easily accessible from the Internet. Users can access measurement logs, while authorized users can change system parameter and restart the unit.
Every unit sends the latest 60 second measurement to a remote central server with ASP.NET application running on it. Unit is now acting as a HTTP client, and using the GET method it appends the parameters to the requested url on the central server. Web application on the server parses this request, extracts the data sent, and inserts it into a database.
Web application also has a web page which displays aggregated measurements from multitude of units, displayed on a map using Google Maps™ API. Every active unit is displayed as a marker on the map. Users clicking on the marker can see the location of the unit, latest measurement with date time stamp. All measurement are color coded throughout the system, so that users can easily estimate state of Gamma radiation at that site just by observing color of the readings. Users can also access historical measurement records for every unit by choosing different time periods, and by optionally choosing isotope for which measurements will be adjusted and displayed accordingly.
Last part of the system is Windows Phone 7 mobile application. It allows users on a move to view data collected from sensing units. This mobile application uses the same database as web application for data storage, but presentation and HCI experience is adjusted for handheld device screen. Application itself is created using the Silverlight™ framework.
Upon start of the application users view all active units as pushpins on a map created using Bing Maps™ API. Tapping on the pushpin message box will appear with the latest measurement and time date stamp of the measurement. Holding a finger or a stylus for a few seconds on a pushpin triggers opening of another page with historical data for that site. Users can choose time period for which they want to review the measurement data. Also here all the measurement records are color coded in uniform pattern with the rest of the system.
The entire module is powered via USB connector which provides +5V DC voltage. This voltage is used directly to power the Microchip microcontroller PIC18F2685, it also provides +3.3 V DC level for ENC28J60 module via the low dropout regulator, and finally it is used in DC/DC converter to produce the +400 V DC voltage for the GM tube.
Reasons for choosing of 18F2685 microcontroller as the processing core of data acquisition module are primarily:
- Low power consumption
- 10 MIPS of processing power
- 96 kB of flash (program) storage
- Built in PWM modulator for DC/DC converter
This microcontroller is also serving in a role of Web server, providing simple html pages to visitors, containing actual measurement as well as giving historical data for the last 12 hours. Every 60 seconds it also sends measurement information to the central server. These functionalities are implemented as add-ons to the Microchip TCP/IP stack functionalities, as well as support for NTP , DHCP protocols, and DynDNS service.
Firmware inside this micro is in charge of providing...Read more »