geiger.py

#!/bin/python

import RPi.GPIO as GPIO
import time

LOG_PERIOD = 20000
MINUTE_PERIOD = 60000

counts = 0
cpm = 0
inputPin = 14 # set input GPIO pin number here

global previousMillis
previousMillis = 0

GPIO.setwarnings(False)
GPIO.setmode(GPIO.BCM)

def geiger_click(channel):
    global counts
    counts = counts + 1

    print "click"

GPIO.setup(inputPin, GPIO.IN)

GPIO.add_event_detect(inputPin, GPIO.RISING, callback=geiger_click)

try:

  while(True):

    currentMillis = int(round(time.time() * 1000))

    if (currentMillis - previousMillis > LOG_PERIOD):
       previousMillis = currentMillis
       cpm = counts * MINUTE_PERIOD / LOG_PERIOD

       print str(cpm) + " cpm"
       counts = 0
except KeyboardInterrupt: # If CTRL+C is pressed, exit cleanly:
    pass
except:
    pass
finally:
    GPIO.cleanup()