Note 6 - Warrants - Warrants Outstanding (Details) - USD ($)		3 Months Ended
		Mar. 31, 2023	Mar. 31, 2022
Balance, outstanding (in shares)		49,023,398	36,765,562
Granted (in shares)		7,512,000	10,393,936
Expired (in shares)		(4,684,986)	(388,889)
Expired, price range (in dollars per share)			$ 0.22
Balance, aggregate intrinsic value	[1]	$ 122,000
Balance, outstanding (in shares)		51,850,412	46,770,549
Minimum [Member]
Balance, outstanding, price range (in dollars per share)		$ 0.13	$ 0.16
Granted, price range (in dollars per share)		0.21	0.20
Expired, price range (in dollars per share)		0.19
Balance, outstanding, price range (in dollars per share)		0.13	0.14
Maximum [Member]
Balance, outstanding, price range (in dollars per share)		1.00	1.00
Granted, price range (in dollars per share)		0.29	0.25
Expired, price range (in dollars per share)		0.35
Balance, outstanding, price range (in dollars per share)		1.00	1.00
Weighted Average [Member]
Balance, outstanding, price range (in dollars per share)		0.26	0.27
Granted, price range (in dollars per share)		0.25	0.22
Expired, price range (in dollars per share)		0.21
Balance, outstanding, price range (in dollars per share)		$ 0.26	$ 0.29

[1] Aggregate intrinsic value based on closing common stock price of $0.20 at March 31, 2023.