Supplemental Balance Sheet Information - Summary of inventories and property plant and equipment (Details) - USD ($)	12 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
Inventories
Work in progress	$ 817,692	$ 288,828
Component parts	8,299,972	7,151,228
Finished goods	1,660,158	1,693,974
Reserve for obsolete and excess inventory	(1,849,134)	(1,800,935)
Inventories	8,928,688	7,333,095
Property, plant and equipment
Total property, plant and equipment at cost	32,806,959	32,048,546
Less accumulated depreciation and amortization	(28,667,266)	(28,047,465)
Property, Plant and Equipment, Net, Total	4,139,693	4,001,081
Other accrued liabilities
Accrued compensation expense	1,257,332	1,149,210
Environmental remediation	514,000	0
Other	334,799	382,197
Accrued Liabilities, Current, Total	$ 2,106,131	1,531,407
Minimum
Property, plant and equipment
Estimated Useful Life	3 years
Maximum
Property, plant and equipment
Estimated Useful Life	35 years
Machinery and equipment
Property, plant and equipment
Total property, plant and equipment at cost	$ 18,831,765	18,073,352
Machinery and equipment | Minimum
Property, plant and equipment
Estimated Useful Life	3 years
Machinery and equipment | Maximum
Property, plant and equipment
Estimated Useful Life	10 years
Buildings
Property, plant and equipment
Total property, plant and equipment at cost	$ 13,055,628	13,055,628
Buildings | Minimum
Property, plant and equipment
Estimated Useful Life	28 years
Buildings | Maximum
Property, plant and equipment
Estimated Useful Life	35 years
Land and land improvements
Property, plant and equipment
Total property, plant and equipment at cost	$ 919,566	$ 919,566
Land and land improvements | Minimum
Property, plant and equipment
Estimated Useful Life	5 years
Land and land improvements | Maximum
Property, plant and equipment
Estimated Useful Life	7 years