Note 6 - Warrants - Warrants Outstanding (Details) - USD ($)	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
Balance, outstanding (in shares)	26,872,430	22,104,817
Balance, outstanding, price range (in dollars per share)	$ 0.42	$ 0.45
Issued (in shares)	24,321,947	6,451,013
Issued, price range (in dollars per share)	$ 0.21	$ 0.23
Expired (in shares)	(7,505,746)	(2,683,400)
Expired, price range (in dollars per share)	$ 0.11	$ 0.40
Balance, outstanding (in shares)	43,688,631	25,872,430
Balance, outstanding, price range (in dollars per share)	$ 0.35	$ 0.39
Balance, aggregate intrinsic value	$ 1,898,000
Minimum [Member]
Balance, outstanding, price range (in dollars per share)	$ 0.25	0.125
Issued, price range (in dollars per share)	0.10	0.25
Expired, price range (in dollars per share)	0.10
Balance, outstanding, price range (in dollars per share)	0.10	0.125
Maximum [Member]
Balance, outstanding, price range (in dollars per share)	1	1
Issued, price range (in dollars per share)	0.30	0.48
Expired, price range (in dollars per share)	0.12	0.40
Balance, outstanding, price range (in dollars per share)	$ 1	$ 1