I promised a water cannon 
for my plants, so I had to deliver, if only for a forum post.
Recap
Green Brain 
is the idea of tracking plant nodes via an industrial CAN bus to ultimately see which plant needs more water cannon .
the idea and the gear
I had the gear for a water cannon. My wife wanted an indoor plant watering system for Christmas so I got her one. But what present is complete without some extra DIY in case I could build one myself. As such I had a few small pumps around. I also had a servo driven X-Y pan and tilt module. How hard can it be to hook that up and make a water cannon.
As an aside, I am also super grateful for a bunch of gear that Element 14 sent to me as a selected challenger.
The pressure is on to use as much of this gear as I can.
Water and electronics
Well there was a lot of learning to be had:
- no matter how well you think you seal things - water will still leak. Although I didn’t go all out with silicon, I thought that tight fitting vinyl tubing, electrical tape and relatively low water pressure would be OK — it was not
- Water brings in fluid dynamics and things like head, flow, nozzle shapes and the like. Clearly my pump could not initially pump up 300mm of head so I moved the motor closer to the nozzle. There would also be time required to refill the tubing up to the nozzle, as once the pump stops the tube empties. Gardening nozzles from a local hardware are only so good at firing a stream of water
- Even small hoses can be stiff enough to move the servos
- Pan and Tilt movement requires some planning in how everything interacts. My platform got tangled in the hose, and the wiring also got stuck every so often for the servos as everything moved around
- Water is heavy and the motion of water in a hose can change the weight balance of everything and move things around
- With all this chaos, I was not bringing the UNO Q anywhere near this water cannon
- Noise, pump motors can produce noise, and that noise can be picked up by the servos and move them haywire around the place
It was this last point that really killed this feature. I had removed the servo library entirely, moved the pump power onto a completely separate circuit isolated by a relay — and still the servos would pan to the right and tilt to the top. Stripping down to a pure diagnostic sketch (no servo code at all) revealed the culprit: the servo signal pins were floating high-impedance inputs, acting as antennas and picking up the pump motor’s EMI directly? maybe? ¯_(ツ)_/¯. Even with no code driving them, the servo controllers saw enough noise to chase a position. I ran out of steam getting this to behave reliably with the full mechanical assembly.
I was hoping to re-use the water cannon as a dog deterrent from scratching a door. I think neither the dogs nor the plants will be seeing any water cannon any time soon.
The only clever things I did was write to EEProm to see if a reboot was happening when the pump kicked in and use the Omega temperature probe to hold the tube that fed water to the pump.
Next
- I have some MAX6675 which would be cool to connect to the K-Type Thermocouples
- there is the Omega Temperature probe
- and I am hoping to at least visualise a little bit of this on NI LabView
oh and there is like 24 hours left 
