February 21, 2013

Wireless Sensing

I haven't posted about soil moisture sensors in ages, but I've completed a number of iterations and I thought it'd be fun to look over the evolution of the hardware. My goal has been to build a small, low power, inexpensive device, that I can place in indoor and outdoor plants to collect soil moisture, light, and temperature readings. I shared some early information on sensors more than a year ago and will have more to share, but this post will focus on the wireless sensor relay.

This device collects readings from one or more sensors at an interval (15 minutes), then broadcasts the readings to a receiver that uploads data to a store where I can crunch numbers, trigger alerts, and generate graphs.

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Continue reading Wireless Sensing.

January 29, 2012

Spherification and Alcohol

Spherification is a "Molecular Gastronomy" technique for making small edible spheres out of just about anything. Since my first flavor sphere experience I've wanted to learn more and make my own.

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Continue reading Spherification and Alcohol.

August 24, 2011

Moisture Sensor: Calibration Round 1

I grow plants. For a time, I've wanted a low-cost sensor that can live in my plants and broadcast information about temperature, light, water, and drainage that I can compare to ideal growing conditions. I've set out to build such a device. This post focuses exclusively on the moisture sensor component.

Commercial grade soil moisture sensors are available, but they are cost-prohibitive for placing in dozens of plants, rather large, and sometimes have very high power requirements for a small device. I'll need to make this component myself.

I have a handful of designs in mind for the sensor. A couple of other hobbyist projects use a variation on the gypsum block sensor:
I've elected for a different design because plaster is quick to absorb moisture and slow to dry. As a result, gypsum block sensors may provide a less granular measure and can inaccurately represent the wetness of the surrounding soil (perhaps I should prove this assertion?).

The designs I'm considering generally share a common component: The sensor is a simple design involving a pair of concentric electrodes, sand as a neutral moisture medium, and a plaster disk to filter out salts or impurities that may cause errors in measurement. These parts are assembled inside a 1/2" plastic tube cap.

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Continue reading Moisture Sensor: Calibration Round 1.