Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Operating activities
Net income (loss)	$ 248	$ (2,636)
Adjustments to reconcile net loss to net cash provided by (used in) operating activities:
Inventory allowance	126	194
Deferred tax benefit	73	(878)
Depreciation and amortization	1,344	1,219
Share-based compensation expense - stock options	129	148
Share-based compensation expense - restricted stock units	142	105
Unrealized (gain) loss on investment in securities	620	(716)
Changes in operating assets and liabilities:
Trade accounts receivable	(2,502)	1,757
Inventories	3,946	(2,241)
Prepaid expenses and other current assets	(145)	669
Other assets	84	(5)
Lease liability	250	90
Accounts payable	(191)	(285)
Accrued compensation and related taxes	364	(743)
Accrued warranty expense	(457)	(298)
Deferred revenue	585	947
Accrued other expenses and other current liabilities	(172)	187
Net cash provided by (used in) operating activities	4,444	(2,486)
Investing activities
Purchases of property, plant and equipment	(946)	(2,455)
Net cash used in investing activities	(946)	(2,455)
Financing activities
Dividends paid	(1,002)	(1,018)
Repurchase of common stock	(269)	(1,041)
Proceeds from issuance of common stock	0	2
Proceeds from debt	2,196	425
Repayment of debt	(2,273)	(19)
Net cash used in financing activities	(1,348)	(1,651)
Net change in cash and cash equivalents	2,150	(6,592)
Cash and cash equivalents, beginning of year	4,676	11,268
Cash and cash equivalents, end of year	6,826	4,676
Supplemental disclosure
Interest paid	22	10
Non-cash financing activity
Common stock issued under restricted stock units	$ 128	$ 147