Note 4 - Stock-based Compensation - Stock Option Activity (Details) - USD ($)	3 Months Ended				9 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Outstanding, shares, Beginning Balance (in shares)	1,351,500	1,372,000	1,376,500		1,376,500
Outstanding, weighted average exercise price (in dollars per share)	$ 0.23	$ 0.23	$ 0.23		$ 0.23
Options granted, shares (in shares)		3,000
Options granted, weighted average exercise price (in dollars per share)		$ 0.21
Options exercised, shares (in shares)	0	(10,000)		0	(10,000)	0
Options exercised, weighted average exercise price (in dollars per share)		$ 0.10
Options expired, shares (in shares)		(11,000)	(4,500)
Options expired, weighted average exercise price (in dollars per share)		$ 0.08	$ 0.13
Options forfeited, shares (in shares)	(2,500)	(2,500)
Options forfeited, weighted average exercise price (in dollars per share)	$ 0.46	$ 0.46
Outstanding, weighted average exercise price (in dollars per share)	$ 0.23	$ 0.23	$ 0.23		$ 0.23
Outstanding, weighted average remaining contractual term (Year)	4 years 62 days
Outstanding, aggregate intrinsic value	$ 11,443				$ 11,443
Exercisable, shares (in shares)	1,321,500				1,321,500
Exercisable, weighted average exercise price (in dollars per share)	$ 0.23				$ 0.23
Exercisable, weighted average remaining contractual term (Year)	4 years
Exercisable, aggregate intrinsic value	$ 11,443				$ 11,443