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Earlier, I discussed my idea to automate some tasks in my upcoming aquaponic greenhouse. These automations will prevent catastrophic failure while I’m away. Since I work an hour from home, it’s paramount that any events that could kill fish or plants are handled immediately and automatically. The first one we’ll discuss and build is leak detection with it’s appropriate response.
A combination of physical design (tank and plumbing) and electronics can be used to attend to the need to minimize (or eliminate) the effects of a leak in the fish tank or sump tank. The tank/plumbing design elements are relatively straightforward:
- Thick enough walls to make it prohibitively difficult to puncture the tank
- Incorporate an anti-siphon element in the solids-lifting overflow (SLO) that moves from the fish tank to the filter and subsequent sump tank
- Don’t hang water heaters where they can rest against the tank wall
- SLO is below the top edge of the tank, preferably by a few inches
- Minimum water level is just below where the water exits the fish tank
- Minimum water level for sump tank is at least two inches above the tallest submerged pump.
Electronic requirements are also pretty straightforward:
- Shut off the pump that refills the offending tank if a leak is detected
- Keep ongoing power consumption to a minimum
- Notify me if/when the tank springs a leak
The electronics design is one of the easiest to understand. At its simplest, a float switch set up in a normally-closed configuration, wired to the pump would turn off the pump if the water fell below the appropriate level. There are a couple of problems with this approach:
- A 120-volt capable float switch is $20 or more, and
- This process doesn’t notify me when the tank springs a leak
If we complicate it just a little, we can get everything we need. If we use a low-voltage float switch wired to a relay and an Arduino or Raspberry Pi, we can control the larger electrical load, log the event, and send a notification.
When the float switch is open, AC power is applied to the pump and it runs. If the switch closes, 5V power is applied to both the relay and notify wire. With power applied to the relay, the NC high-voltage side is opened, cutting off power to the pump. The 5V applied to the notify wire tells the microprocessor (or computer) to process the interrupt code.
By starting here with an expandable computerized system, we can add other capabilities when we’re ready to implement them. Next time, I think we’ll look at temperature monitoring.