Note 8 - Segment Reporting (Details) - Segment Reporting (USD $)
3 Months Ended 9 Months Ended
Jan. 31, 2014
Jan. 31, 2013
Jan. 31, 2014
Jan. 31, 2013
Apr. 30, 2013
Segment Reporting Information [Line Items]          
Total revenues $ 7,683,000 $ 7,458,000 $ 21,787,000 $ 17,853,000  
Gross margin 2,922,000 2,803,000 8,158,000 6,603,000  
Goodwill 1,942,000 1,942,000 1,942,000 1,942,000 1,942,000
Original Equipment Manufactures [Member]
         
Segment Reporting Information [Line Items]          
Total revenues 3,032,000 4,424,000 10,930,000 9,968,000  
Gross margin 698,000 1,226,000 2,772,000 2,574,000  
Goodwill 0 0 0 0  
Proprietary Products [Member]
         
Segment Reporting Information [Line Items]          
Total revenues 4,651,000 3,034,000 10,857,000 7,885,000  
Gross margin 2,224,000 1,577,000 5,386,000 4,029,000  
Goodwill $ 1,942,000 $ 1,942,000 $ 1,942,000 $ 1,942,000