Accounts receivable (Details) - USD ($)	Jul. 31, 2015	Apr. 30, 2015
Receivables [Abstract]
Trade receivables	$ 2,770,000	$ 2,151,000
Other receivables	32,000	160,000
Allowance for doubtful accounts and sales returns	130,000	140,000
Accounts receivable	$ 2,672,320	$ 2,170,261