The Plant Water'er

Problem: It's the dog days of summer. You own a bunch of nice plants that need frequent watering, and are about to leave on a 2 week vacation. How do you keep the plants alive? Hint: Assume friends or roommates are negligible.

This has been a serious, ongoing problem in my life. The best solution would be to just raise cacti and aloe, but I like to keep things complicated.

V 1.0 Handi-water
My undergraduate solution at Illinois.



After several weeks of experiments, I finally decided on a bottle/rubber combo that 'failed' after 3-4 days, drenching the plant with water. Perfect for a weeklong vacation! My success rate was very good, I remember only one water reservoir didn't trigger.
My neighbors must have thought I was totally insane. They were probably right.

Fast forward 3+ years.



After two grad courses in mechatronics, I figured an electrical version was easily within reach. V 2.0 consisted of a nice little beverage solenoid valve powered by a 12 v battery and a NPN power transistor triggered by a photocell.

Barely readable circuit sketch:



What is going on:
When my room phone rings, an orange LED on the front blinks rapidly. I used the blinky light as my external trigger by taping a photocell to the phone cover (non invasive!). I was very happy with the photocell response, nearly an order of magnitude swing when exposed to light. The photocell is represented in the diagram above as the left, topmost resistor-- it basically acts as light-sensitive variable resistor. This drop in Resistance pulls V_GS (gate to source voltage; V_th = 4) high enough to turn the MOSFET 'on'. This then activated the right-hand side of the circuit-- current can now flow from the battery and through the solenoid coil, electrically opening the valve. Quite simple, really.
[In case you were wondering, the diode in parallel with the solenoid coil helps to snub the inductive voltage spike experienced during turnoff. It basically protects the MOS transistor.]

My first water reservoir was a small .9 fluid oz bottle routed to the valve and plants via 1/8" flexible plastic tubing. It hung precariously from my window by some frayed blue yarn.



V 2.1 upgrade consisted of a larger water reservoir and larger tube diameter for increased flowrate. It still hung precariously by some frayed blue yarn . Watch the Plant Water-er in action* last summer!

The next step, naturally, is to fully automate the watering process. You'd place a small sensor in the soil that somehow detects wet-ness (probably again through resistance). The solenoid valve would turn on periodically, when the plants got too dry-- no calling necessary!

I'll post updates as I improve this system. However, there are other projects I'm going to attempt first.

*Remind me to never talk in any videos again ever. Listening to me stumble through simple sentences is painful.