Note 7 - Stock Options - Details of Options Outstanding (Details) - $ / shares	3 Months Ended
	Mar. 31, 2023	Dec. 31, 2020
Exercise price (in dollars per share)	$ 0.50	$ 0.49
Number of options outstanding (in shares)	5,415,000	5,315,000
Number of options exercisable (in shares)	4,701,000
Range One [Member]
Exercise price (in dollars per share)	$ 0.350
Number of options outstanding (in shares)	3,600,000
Number of options exercisable (in shares)	3,600,000
Remaining contractual life (Year)	3 months 21 days
Range Two [Member]
Exercise price (in dollars per share)	$ 0.450
Number of options outstanding (in shares)	250,000
Number of options exercisable (in shares)	200,000
Remaining contractual life (Year)	8 months 23 days
Range Three [Member]
Exercise price (in dollars per share)	$ 1.200
Number of options outstanding (in shares)	500,000
Number of options exercisable (in shares)	400,000
Remaining contractual life (Year)	9 months 29 days
Range Four [Member]
Exercise price (in dollars per share)	$ 0.800
Number of options outstanding (in shares)	375,000
Number of options exercisable (in shares)	225,000
Remaining contractual life (Year)	1 year 2 months 12 days
Range Five [Member]
Exercise price (in dollars per share)	$ 0.600
Number of options outstanding (in shares)	590,000
Number of options exercisable (in shares)	236,000
Remaining contractual life (Year)	1 year 6 months 14 days
Range Six [Member]
Exercise price (in dollars per share)	$ 0.800
Number of options outstanding (in shares)	100,000
Number of options exercisable (in shares)	40,000
Remaining contractual life (Year)	1 year 10 months 2 days