The goal is to grow tomatoes, chilis, carrots, lettuce and spinach on my balcony. It shall be hydroponic and as much automated as possible. Here's my setup so far ...
Plumbing and Dutch-buckets
No rocket since here. It's all made from 1/2 inch PCV pipe and fittings from the hardware store. The buckets were done according to these excellent instructions by mhpgardener. As I wanted the setup to be removable, I didn't use any glue. To achieve a good seal anyway, I used a bit of silicone grease on all fittings. So far it holds up fine.
Dosing pump assembly
This contraption shall refill the reservoir with fresh water from the tap and add small amounts of plant food, ph-stabilizer and hydrogen peroxide. I'm using cheap peristaltic dosing pumps and a solenoid valve from ebay.
The pumps feed into a 1 inch PCV pipe, which will guide the liquids directly into the reservoir.
A 3D model has been designed in Fusion360, which helped to lay out the pumps in a space-saving pattern and to keep the piping as short as possible.
The 3D model is available here: http://a360.co/2sLctMa
The two plates were laser-cut from 6 mm acrylic sheet. Pro tip: take apart old flat-screen monitors and extract the light-guide assembly behind the LCD. This is an excellent source of high-quality acrylic sheet material.
PH - Probe interface
Basically it's a voltage follower driving an inverting amplifier. Trick is to keep one end of the ph-probe at a certain bias voltage, so positive and negative voltages can be read with only a single supply. Some initial simulations were done in LT-Spice.