Monthly Archives: September 2012

electric imps have arrived!

No, it’s not some weird computer virus: electric imps are the solution I’ll be using for wifi on growerbot. It’s taken some negotiation and time, but I’ve finally received 100 of the SD-card-sized devices:

More detail on electric imp here. My favorite thing about this shipment is the logo on the box: it’s hand-drawn with permanent marker! Did I mention electric imp is a young startup?:)

Growerbot is going to be one of if not the first device in the world to ship with this wifi solution; based on a bunch of testing I’ve done, I’m convinced you’ll be quite happy with it. This and other component choosing/sourcing difficulties may push back delivery by a few weeks, but they’re also making growerbot even more cutting-edge. I promise it’ll be worth the wait!


Here are the planned component connections, breadboard-style via Fritzing:

It’s a lot less complicated than it looks: most of the wiring is for the LCD. The kit and turnkey versions will both use a custom PCB to make adding or removing components much more straightforward: I’m planning to use lines of headers, placing needed connections in a neat row, while maintaining functionality of the existing pins.

Choosing Temperature, Humidity, Light, and Moisture Sensors


I’ve decided on the core 3 sensors for growerbot:

  • Temperature / Humidity: DHT22. .5C temperature and +/-2% humidity accuracy. Datasheet (pdf).
  • Light: TSL2561. .1 to 40,000 lux, with separate sensors for infrared and full spectrum. Datasheet (pdf).
  • Moisture: 2mm corrosion-resistant stainless steel rods of consistent length (probably gonna use 1″) mounted a fixed distance apart. McMaster part #1335t21, although I’ve heard I can just use stainless steel TIG welding rod as well…
Here’s approximately what the DHT22 and TSL2561 look like:

 and TSL2561 digital luminosity / lux / light sensor

For the light sensor, I’m still debating whether to buy the Adafruit breakout (pictured above) or do my first-ever surface-mount soldering with the individual chip instead. Any alternative suggestions for sensors I should consider, please let me know!