Chad Lawson is posting a series of videos about learning to make things on his site at verbosemode.tv.
Thanks for the kind words, Chad!
(photo credit: alvaroprieto)
This year I decided (in true last-minute fashion) to build a couple demos to show off my Geiger Counter kit at the Maker Faire Bay Area. One of these demos used my Geiger Counter kit to create ambient music:
(Thanks to @j_jwalrus for the interview and video!)
The PULSE output of each Geiger counter is connected to one input of a 74LS04 hex inverter on the Protoshield. Each time a Geiger counter detects a radioactive decay, it sends a 0.1ms 3V high pulse to one input of the inverter. The 74LS04 functions as a level shifter and outputs an (inverted) 5V pulse that is suitable for driving an ordinary (5V) Arduino.
Five outputs of the 74LS04 are connected to input pins on the Arduino. For convenience, I used Analog inputs 0-1 as digital input pins. The rest of the gates are connected to digital pins 10-12.
I used the PinChangeInt library on the Arduino to trigger an interrupt handler every time a falling edge is detected on one of the geiger inputs. This interrupt handler stores the pin number to a variable and sets a flag to tell the main() function that something has happened.
The main() loop polls the interrupt flag and waits for something to happen. When it detects that an interrupt has occured, it sends a “Note On” midi message to the Music Instrument Shield, using the SoftwareSerial library built in to Arduino 1.0. I had to hack the library a bit to get it to work in conjuction with the PinChangeInt library, since the SoftwareSerial library automatically installs interrupts for all pins (bad, bad SoftwareSerial!)
The value of the note depends on which Geiger counter triggered the interrupt. In the video I am using note ‘C’ over five octaves, centered around middle C (midi note 60). (I am not a musician, but this seemed to provide a pleasing sound that wouldn’t annoy me or my neighbors at the Faire too much.)
The Arduino sketch is a complete disaster right now, having been thrown together at the last minute, but I plan to clean it up and post it soon.
Things I learned while creating this demo:
If you squint at the laptop in the video, you can see that his geiger counter is reading over 400 CPM!
Christoph sent me his data logs, which clearly show the effect of altitude on radiation exposure:
The red trace is the background level on the ground in SFO and hovers around 20 CPM. The blue trace is the measured radiation over Greenland on his transatlantic flight. The peak readings are 25 times the background radiation at sea-level!
Caution: Unless you like being hassled by the TSA, I don’t recommend flying with the Geiger kit in your carry-on luggage, much less actually using it on the plane! On his DIY Geiger Counter site, Brohogan posted some good advice about traveling with a Geiger counter.
Have you done something cool with your Geiger Counter kit? If so, post about it in the forums!
If anyone knows where to find more of these displays, I would love to get my hands on some!