After problems with not getting enough nutrient to my system (stalling air-lift) I now have the opposite problem, waterlogged plants!

The airlift is providing too much flow and the seedlings are getting too much watering – there cannot be enough air getting to them

After having a good laugh at the prices of interval timer/switch units I have decided to construct an electronic circuit to do this.

That may sound a big deal – but as we don’t care too much about the accuracy of the intervals or the duration of the “on” period I should be able to produce a very simple circuit (cost circa £8 – £5 if you already have a spare 12 volt supply kicking around) to swith the pump on for say 30 minutes and switch off for say 2 hours (but I will make the periods adjustable)

I will upload a circuit when it’s prototyped but it should be within the capabilities of anyone who can use a soldering iron.

OK I’m uploading a circuit BEFORE it’s prototyped/tested so don’t complain if it does not work!

untested v1 - HyTime