Income taxes, Deferred tax assets and liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Deferred tax assets [Abstract]
Foreign net operating losses	$ 538	$ 390
Depreciation	165	71
Inventory reserves	916	879
Deferred revenue	58	16
Warranty reserve	47	60
Stock compensation expense	701	682
Other accrued compensation	226	233
R&D credit carryforward	111	0
Other liabilities and reserves	276	278
Gross deferred tax assets	3,038	2,609
Valuation allowance	(444)	(390)
Net deferred tax assets	2,594	2,219
Deferred tax liabilities [Abstract]
Other	29	21
Net deferred tax liabilities	29	21
Total net deferred tax assets	$ 2,565	$ 2,198