Condensed Consolidated Statements of Operations and Comprehensive Income (Loss) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Oct. 31, 2021	Oct. 31, 2020	Oct. 31, 2021	Oct. 31, 2020
Income Statement [Abstract]
Revenues	$ 12,936	$ 13,990	$ 25,890	$ 26,940
Cost of revenues	8,845	8,668	17,738	17,530
Gross margin	4,091	5,322	8,152	9,410
Selling and administrative expenses	2,411	4,124	6,805	7,352
Research and development expenses	1,377	979	2,732	2,177
Operating income (loss)	303	219	(1,385)	(119)
Other income (expense):
Investment income	98	50	191	157
Interest expense	(20)	(36)	(40)	(75)
Other income (expense), net	118	113	158	129
Income (loss) before provision for income taxes	499	346	(1,076)	92
Provision for income taxes	2	17	2	25
Net income (loss)	$ 497	$ 329	$ (1,078)	$ 67
Net income (loss) per common share:
Basic and diluted income (loss) per share (in Dollars per share)	$ 0.05	$ 0.04	$ (0.12)	$ 0.01
Weighted average shares outstanding:
Basic (in Shares)	9,256,255	9,169,758	9,246,240	9,154,434
Diluted (in Shares)	9,301,528	9,235,777	9,246,240	9,205,823
Condensed Consolidated Statements of Comprehensive Income (Loss)
Net income (loss)	$ 497	$ 329	$ (1,078)	$ 67
Unrealized (loss) gain on marketable securities:
Change in market value of marketable securities before reclassification, net of tax	(157)	(176)	(72)	5
Reclassification adjustment for realized gains included in net income, net of tax	0	0	(6)	(10)
Total unrealized (loss) gain on marketable securities, net of tax	(157)	(176)	(78)	(5)
Comprehensive income (loss)	$ 340	$ 153	$ (1,156)	$ 62