Segment information (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Apr. 04, 2015	Mar. 29, 2014	Apr. 04, 2015 Segment	Mar. 29, 2014
Segment information [Abstract]
Number of reportable segments			2
Segment Reporting Information, Revenue for Reportable Segment [Abstract]
Sales to external customers	$ 10,340	$ 9,170	$ 20,273	$ 18,219
Operating income (loss)	674	196	956	906
Identifiable assets, excluding goodwill	30,303	24,142	30,303	24,142
Reportable Segments [Member] | Controls [Member]
Segment Reporting Information, Revenue for Reportable Segment [Abstract]
Sales to external customers	9,761	8,601	19,180	17,136
Operating income (loss)	374	190	722	839
Identifiable assets, excluding goodwill	21,977	22,220	21,977	22,220
Reportable Segments [Member] | Capacitors [Member]
Segment Reporting Information, Revenue for Reportable Segment [Abstract]
Sales to external customers	579	569	1,093	1,083
Operating income (loss)	80	104	116	144
Identifiable assets, excluding goodwill	1,148	1,341	1,148	1,341
Intersegment Eliminations [Member]
Segment Reporting Information, Revenue for Reportable Segment [Abstract]
Sales to external customers	1	2	3	2
Intersegment Eliminations [Member] | Controls [Member]
Segment Reporting Information, Revenue for Reportable Segment [Abstract]
Sales to external customers	0	0	0	0
Intersegment Eliminations [Member] | Capacitors [Member]
Segment Reporting Information, Revenue for Reportable Segment [Abstract]
Sales to external customers	1	2	3	2
Corporate [Member]
Segment Reporting Information, Revenue for Reportable Segment [Abstract]
Sales to external customers	0	0	0	0
Operating income (loss)	220	(98)	118	(77)
Identifiable assets, excluding goodwill	$ 7,178	$ 581	$ 7,178	$ 581