Note 6 - Warrants (Tables)

12 Months Ended

Dec. 31, 2019

Notes Tables

Schedule of Stockholders' Equity Note, Warrants or Rights [Table Text Block]

	Warrants outstanding			Exercise   price per share			Weighted a verage p rice per share		Aggregate intrinsic value (1)
Balance, December 31, 2017		22,104,817		$0.25	–	1.00	$	0.45		--
Granted		7,451,013		0.25	–	0.48		0.29
Expired		(2,683,400	)		0.40			0.40
Balance, December 31, 2018		26,872,430		$0.25	–	1.00	$	0.43		--
Granted		24,490,687		0.25	–	0.48		0.29
Exercised		(7,544,456	)		0.30			0.30
Expired		(587,500	)		0.40			0.40
Balance, December 31, 2019		43,231,161		$0.25	–	1.00	$	0.43		--

Schedule Of Assumptions Used To Determine Fair Value Of Warrants [Table Text Block]

	2018			2019
Risk free interest rate	2.54	–	3.00%	1.42	–	2.13%
Expected volatility	105	–	127%	101	–	110%
Expected dividend yield		—			—
Forfeiture rate		—			—
Expected life in years	3	–	5	1	–	5