Note 5 - Warrants - Warrants Outstanding (Details) - $ / shares	6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016
Issued (in shares)	990,727	1,828,571
Issued, price range (in dollars per share)		$ 0.45
Expired (in shares)	(510,000)	(183,545)
Beginning balance, outstanding (in shares)	20,035,114	13,779,438
Expired, price range (in dollars per share)		$ 0.55
Ending balance, outstanding (in shares)	20,515,841	15,424,464
Minimum [Member]
Issued, price range (in dollars per share)	$ 0.42
Beginning balance, outstanding, price range (in dollars per share)	0.25	$ 0.125
Beginning balance, outstanding, price range (in dollars per share)	0.125
Ending balance, outstanding, price range (in dollars per share)	0.125
Maximum [Member]
Issued, price range (in dollars per share)	0.70
Beginning balance, outstanding, price range (in dollars per share)	0.30	$ 1
Beginning balance, outstanding, price range (in dollars per share)	1
Ending balance, outstanding, price range (in dollars per share)	$ 1