8. Income Taxes (Details 2) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Deferred tax assets:
Operating loss carryforwards	$ 1,238	$ 1,347
R&D tax credit	1,952	1,678
AMT tax credit	0	72
Section 263A costs	203	294
R&D costs	0	110
Amortization	21	24
Unrealized loss	391	252
Asset reserves:
Bad debts	11	11
Inventory allowance	118	187
Accrued expenses:
Non-qualified stock options	175	132
Compensation	64	132
Warranty	927	904
Deferred tax assets	5,098	5,143
Less valuation allowance	(98)	0
Total deferred tax assets	5,000	5,143
Deferred tax liabilities:
Depreciation	(700)	(770)
Total deferred tax liabilities	(700)	(770)
Net deferred tax assets (before unrealized gain)	4,300	4,373
Deferred tax liability: unrealized gain	0	0
Net deferred tax assets	$ 4,300	$ 4,373