I am electronics engineer but my hobby is fishing. In my area fishermen use a technique where squids must stay alive for a few days. For that use squids are in plastic tank with pump for fresh water.
My timer automatically turns the live bait pool pump on and off at selected intervals. In this way, the bait stays alive for a long time and at the same time the battery is saved.
The pump operating interval is set with a potentiometer from 1 to 15 minutes and the pause interval via a corresponding potentiometer from 2 to 30 minutes. There is also a switch on the panel with the selection OFF, Bypass (constant operation, used when filling the pool) and Timer (mode where the timer periodically turns the pump on and off).
First idea was to make it for use on my boat but now I produce about 200 per month and sell it all around the globe. Thank you 555 :)