Note 7 - Stockholders' Equity - Stock-based Compensation (Details) - USD ($)	3 Months Ended
Mar. 31, 2020	Mar. 31, 2019
Stock-based compensation	$ 67,000	$ 81,000
Selling and Marketing Expense [Member]
Stock-based compensation	13,000	12,000
Research and Development Expense [Member]
Stock-based compensation	15,000	15,000
General and Administrative Expense [Member]
Stock-based compensation	$ 39,000	$ 54,000

Amount of expense for award under share-based payment arrangement. Excludes amount capitalized.

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