We had a great meeting in March. Eric Maundu gave a great over view of the chemistry and system used in aquaponics. Basically it consists of a fish tank and a growing bed. To keep the tank clean water is pumped to the bed where bacteria break down the fish waste and feed the plants. Then the water is pumped back into the tank and the cycle repeats itself. Eric explained how this flow matches what nature already does only on a much smaller scale. For more information on Eric’s projects go to Kijiji Grows
Eric Maundu talks about the aquaponics cycle at Tech Liminal
Then Rik Kretzinger demoed his Arduino automated unit. The cycle starts with a pump that fills the grow bed. The water level is detected by a media probe. When the signal from the probe is big enough the Arduino shuts off the pump and then waits a set amount of time. Then it activates a gravity feed valve that empties the tank. When the media probe signals the tank is empty the Arduino waits a set amount of time and then starts the cycle over again. All of which is pretty neat 
For more information see Rik’s page on the The Aquapanics Gardening Community.
Rik demos his aquaponics system at the Tech Shop
Then we did our soft circuits miniproject and people went home with some great LED bracelets. This project used conductive thread to connect a battery to a LED. When the bracelet was snapped together it would close the circuit and light up the LED.