UNAUDITED CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jul. 01, 2018	Jun. 30, 2019	Jul. 01, 2018
Income Statement [Abstract]
Revenue	$ 2,087	$ 3,122	$ 5,281	$ 5,886
Cost of revenue	1,065	1,592	2,280	2,967
Gross profit	1,022	1,530	3,001	2,919
Operating expenses:
Research and development	3,215	2,366	6,457	5,065
Selling, general and administrative	2,340	2,610	4,786	5,171
Total operating expenses	5,555	4,976	11,243	10,236
Loss from operations	(4,533)	(3,446)	(8,242)	(7,317)
Interest expense	(124)	(32)	(207)	(56)
Interest income and other (expense), net	50	23	98	9
Loss before income taxes	(4,607)	(3,455)	(8,351)	(7,364)
Provision for (benefit from) income taxes	27	29	(241)	90
Net loss	$ (4,634)	$ (3,484)	$ (8,110)	$ (7,454)
Net loss per share:
Basic and diluted	$ (0.05)	$ (0.04)	$ (0.09)	$ (0.09)
Weighted average shares outstanding:
Basic and diluted	99,226	85,753	98,032	83,176