Condensed Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Cash flows from operating activities
Net loss	$ (4,934)	$ (8,068)
Adjustments to reconcile net loss to net cash used in operations:
Depreciation and amortization	246	552
Gain on disposal of fixed assets	(450)	0
Share-based compensation expense	189	351
Inventory write-downs	168	0
Change in:
Accounts receivable, net	527	202
Costs and estimated earnings in excess of billings on uncompleted contracts	0	(212)
Inventory	24	47
Other current and non-current assets	451	220
Accounts payable	242	(193)
Accrued liabilities	(1,208)	(332)
Deferred revenue	(6)	0
Billings on uncompleted contracts in excess of related costs	0	5
Other currrent liabilities	(525)	(59)
Operating lease liabilities	(161)	(160)
Net cash used in operating activities	(5,437)	(7,647)
Cash flows from investing activities
Proceeds on sale of property and equipment	525	0
Purchases of property and equipment	(75)	(313)
Net cash provided by (used in) investing activities	450	(313)
Cash flows from financing activities
Principal payments under finance leases	(6)	(4)
Net proceeds from issuance of common stock	1,481	1,177
Net cash provided by financing activities	1,475	1,173
Change in cash and cash equivalents, and restricted cash	(3,512)	(6,787)
Cash, cash equivalents and restricted cash at beginning of period	6,272	14,201
Cash, cash equivalents and restricted cash at end of period	2,760	7,414
Supplemental schedule of non-cash investing and financing activities
Non-cash additions to property and equipment	$ 37	$ 221