Condensed Consolidated Statements of Operations and Comprehensive Income (Loss) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jan. 31, 2022	Jan. 31, 2021	Jan. 31, 2022	Jan. 31, 2021
Income Statement [Abstract]
Revenues	$ 12,245	$ 11,672	$ 38,136	$ 38,612
Cost of revenues	9,005	8,868	26,744	26,398
Gross margin	3,240	2,804	11,392	12,214
Selling and administrative expenses	2,832	2,454	9,637	9,805
Research and development expenses	1,129	1,289	3,861	3,466
Operating loss	(721)	(939)	(2,106)	(1,057)
Other income (expense):
Investment income	4	160	195	316
Interest expense	(19)	(9)	(59)	(84)
Other income (expense), net	2	0	160	129
Loss before provision for income taxes	(734)	(788)	(1,810)	(696)
Provision for income taxes	1	12	3	37
Net loss	$ (735)	$ (800)	$ (1,813)	$ (733)
Net loss per common share:
Basic and diluted loss per share (in Dollars per share)	$ (0.08)	$ (0.09)	$ (0.2)	$ (0.08)
Weighted average shares outstanding:
Basic and diluted (in Shares)	9,278,840	9,185,235	9,257,107	9,164,714
Condensed Consolidated Statements of Comprehensive Loss
Net loss	$ (735)	$ (800)	$ (1,813)	$ (733)
Unrealized loss on marketable securities:
Change in market value of marketable securities before reclassification, net of tax	(211)	(22)	(283)	(18)
Reclassification adjustment for realized gains included in net income, net of tax	2	(12)	(4)	(21)
Total unrealized loss on marketable securities, net of tax	(209)	(34)	(287)	(39)
Comprehensive loss	$ (944)	$ (834)	$ (2,100)	$ (772)