Note 14 - Product Line and Geographic Information - Sales by Geographic Region (Details) - USD ($) $ in Thousands		12 Months Ended
		Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2018
Net sales		$ 31,899	$ 30,202	$ 34,115
Geographic Concentration Risk [Member]
Net sales	[1]	$ 31,899	$ 30,202	$ 34,115
Net sales, percent	[1]	100.00%	100.00%	100.00%
Geographic Concentration Risk [Member] | UNITED STATES
Net sales	[1]	$ 24,855	$ 24,192	$ 26,348
Net sales, percent	[1]	78.00%	80.00%	77.00%
Geographic Concentration Risk [Member] | Asia Pacific [Member]
Net sales	[1]	$ 1,848	$ 2,597	$ 3,238
Net sales, percent	[1]	6.00%	9.00%	9.00%
Geographic Concentration Risk [Member] | Europe [Member]
Net sales	[1]	$ 3,659	$ 2,316	$ 2,540
Net sales, percent	[1]	11.00%	8.00%	8.00%
Geographic Concentration Risk [Member] | Other Countries [Member]
Net sales	[1]	$ 1,537	$ 1,097	$ 1,989
Net sales, percent	[1]	5.00%	3.00%	6.00%

[1] Net sales are attributed to countries based on location of customer.